Victor Charpenay
email: victor.charpenay@emse.fr

Tobias Käfer
email: tobias.kaefer@kit.edu

Andreas Harth
email: andreas.harth@fau.de

A Unifying Framework for Agency in Hypermedia Environments

Keywords: Semantic Web, Linked Data, Hypermedia, Multi-Agent System 5

One of the emerging trends in engineering multi-agent systems (MASs) is to use the Web as an environment. On the Web, hypermedia is the guiding principle of agent perception and action. Web standards allow agents to have a single uniform interface to their environment, be it real or simulated. Most recent proposals for hypermedia MASs tend, however, to introduce a coupling between agents and their environment. This paper introduces a framework based on Semantic Web technologies to formalize interactions between agents and a hypermedia environment. Semantic Web technologies and, more specifically, Web ontologies guarantee interoperability on the Web and maximize uncoupling between components. We show how existing ontologies can be used to make existing MAS prototypes fit our framework. Our framework formalizes state transfer, the guiding principle of agentenvironment interactions in hypermedia, with respect to a reference formalism originally introduced by Genesereth and Nilsson. We also show the equivalence between the two in the paper, under certain conditions.

Introduction

"On the Internet, nobody knows you're an autonomous agent." The quote 4 emphasizes the fact that Web servers have no means to distinguish between human agents and autonomous agents (or 'bots') that perform request according to a predefined plan. Conversely, agents have no means to assert the origin of a resource, whether it was e.g. created by another agent in relation to physical world events or simulated/forged.

Generally speaking, the architecture of the Web provides a uniform information space that agents can manipulate, through hypermedia [START_REF] Jacobs | Architecture of the world wide web, volume one. W3C Recommendation[END_REF]. As such, the Web has been seen as a good candidate architecture for building multi-agent systems (MASs) since at least the 2000s [START_REF] Hendler | Agents and the semantic web[END_REF]. At the time, it was envisioned that autonomous agents could browse the Web as humans do and perform informed actions, such as buying commercial goods online and negotiating prices. To that end, preliminary work on Web ontologies and machine understanding started, to eventually be standardized by the World Wide Web Consortium (W3C) as Semantic Web technologies: RDF, SPARQL and OWL, the Web Ontology Language. In 2010, James Hendler and Tim Berners-Lee underline the importance of Semantic Web technologies to build "social machines" on the Web [START_REF] Hendler | From the Semantic Web to social machines: A research challenge for AI on the World Wide Web[END_REF].

Meanwhile, Semantic Web technologies have evolved and deviated from the original vision of autonomous Web agents. However, the Semantic Web is now entering novel domains of applications that revive the need for agent-oriented programming. The Web of Things 5 (WoT) and the Social Web 6 , as standardized by the W3C, are two such domains. The Web of Things allows for new forms of industrial control that tend towards self-organization, a characteristic that is often associated with agent-based modeling [START_REF] Wilensky | An introduction to agent-based modeling: modeling natural, social, and engineered complex systems with NetLogo[END_REF]. The Social Web allows for uniform human-to-human and human-to-machine interactions, e.g. with chatbots. Most W3C standards for WoT and the Social Web reuse and extend Semantic Web technologies, narrowing the gap between the original vision of autonomous agents on the Web and available technologies.

In the MAS literature, various research prototypes with WoT and social Web applications have been recently proposed, in particular among the workshop series on Engineering MASs (EMAS) [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF][START_REF] Casals | Exposing agents as web services in JADE[END_REF][START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF][START_REF] Collenette | Multi-agent control of industrial robot vacuum cleaners[END_REF]. However, most of these proposals do not use Semantic Web technologies (only one proposal does [START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF], although another includes Linked Data-a subfield of the Semantic Web-as future work) [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF].

Not using Semantic Web technologies such as RDF and OWL 7 , has a direct consequence: agents can neither be developed independently from each other, nor can their environment (which includes e.g. WoT 'things' or a social networking platform) be developed independently from them. Such coupling between agents and their environment go against the promise of hypermedia of unifying information management. Yet, as we will see in Sec. 2, if one strictly applies hypermedia principles to MAS architectures, certain architectures with direct agent-to-agent interactions may not be realizable on the Web.

In this paper, we introduce a unifying framework, rooted in RDF, for agents situated on the Web. This framework applies the usual Semantic Web abstrac-tions (RDF triples, resources and datasets) to MAS architectures, to maximize decoupling between system components. We make no assumption as to agent architectures but rather characterize interactions between agents and their (hypermedia) environment in abstract terms. To that end, we base our framework on a formalism first introduced by Genesereth and Nilsson [START_REF] Genesereth | Logical Foundations of Artificial Intelligence[END_REF], which is, to the best of our knowledge, the most commonly accepted formalism of the sort. We show how to reconcile hypermedia principles, a subset of the Representational State Transfer (REST) principles [START_REF] Fielding | Architectural Styles and the Design of Network-based Software Architectures[END_REF], and MAS architectures, such that any classical MAS (as defined by Genesereth and Nilsson) has an equivalent hypermedia MAS.

In the next section (Sec. 2), we analyse recent EMAS prototypes with respect to the REST principles and identify potential limitations to address in our formalism. We then move on to the main contribution of the paper: a MAS formalism based on RDF (Sec. 3) and evaluate the feasability of implementing MASs according to our framework, by providing examples of RDF and OWL ontologies that the reviewed EMAS prototypes could leverage (Sec. 4). We conclude the paper in Sec. 5.

Related Work

Cyber-Physical Systems on the Web & Hypermedia

Recent research initiatives demonstrate renewed interest for topics at the intersection of autonomous agents and the Web. A workshop on hypermedia MASs took place at TheWebConf in 2019 8 , followed by a Dagstuhl-Seminar on the same topic in 2021 9 .

Papers emanating from the EMAS series of workshops confirm this trend. The Web appears in three papers, either as a scalable distributed system made of Web services [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF][START_REF] Casals | Exposing agents as web services in JADE[END_REF] or as a uniform interface to cyber-physical systems [START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF]. In all three papers, WoT is invoked as a new domain of application for autonomous agents. A fourth paper even makes use of WoT principles without naming them: its prototype indeed involves controlling physical devices via a Web API [START_REF] Collenette | Multi-agent control of industrial robot vacuum cleaners[END_REF].

Two of these EMAS prototypes insist on hypermedia as the main distinctive feature of their approach [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF][START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF]. Ciortea et al. insist on the fact that hypermedia helps agents "discover at runtime other entities in a MAS and the means to interact with those entities". Runtime discovery is made possible by the interlinking of Web resources (via hyperlinks) such that agents can navigate from one resource to the other. Web resources should further include pointers to potential actions (via Web forms). These hypermedia design principles are part of the REST architectural principles, which have conditioned much of the architecture of the Web itself [START_REF] Fielding | Architectural Styles and the Design of Network-based Software Architectures[END_REF]. The recent WoT standards published by the W3C [START_REF] Kovatsch | Web of Things (WoT) architecture. W3C Recommendation[END_REF][START_REF] Kaebisch | Web of Things (WoT) thing description. W3C Recommendation[END_REF] acknowledge the importance of hypermedia on the Web and define interactions between a 'thing' (a Web server) and a WoT 'consumer' (a Web client) in terms of links and forms.

Autonomous Agents and Representational State Transfer

The benefits of hypermedia as a mechanism unifying agent interactions only hold if the links and forms embedded in Web resources have shared semantics among agents, as underlined in introduction. RDF, the Resource Description Framework, allows agents to discover the semantics of hyperlinks at runtime as well, by making link relation types themselves dereferenceable resources. As a result, every statement about a Web resource is a hyperlink (an RDF triple), which creates an interdependency between the representation of a resource (as a set of RDF triples) and its location on the Web (via a URI).

This interdependency between representation and location on the Web makes REST an important requirement in Semantic Web applications. In particular, the REST constraint that a hypermedia system has to be layered ensures the proper addressing of semantic resources by so called 'origin servers'. This constraint, known as the 'layered system' constraint is one of the six architectural constraints of REST. It implies that "the large-grain data flows of hypermedia interaction can each be processed like a data-flow network, with filter components selectively applied to the data stream in order to transform the content as it passes" [START_REF] Fielding | Architectural Styles and the Design of Network-based Software Architectures[END_REF]. In REST, there is a sharp distinction between origin servers, which provide data at one end of the data stream, and 'user agents', which collect data at the other end of the stream.

In a hypermedia MAS, however, agents play both roles: they may in turn be origin servers and user agents. As a result, the hypermedia system would not be layered anymore, wherever data flows give form to cycles among components. Fig. 1 shows the different data flows that have been implemented in the four EMAS prototypes previously mentioned. In the two prototypes featuring Web services [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF][START_REF] Casals | Exposing agents as web services in JADE[END_REF], an agent is a mixed component that includes both a server connector (for perception and agent-to-agent interactions) and a client connector (for action), enabling direct interactions with other agents (Fig. 1a). In the prototype involving a Web API to physical devices [START_REF] Collenette | Multi-agent control of industrial robot vacuum cleaners[END_REF], agents have a pure client role while servers are purely reactive components translating remote control into physical phenomena. In this application, servers are thus genuine origin servers (Fig. 1b). Finally, the prototype by Ciortea et al. [START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF] does include origin servers but it also uses WebSub [START_REF] Genestoux | Websub. W3C Recommendation[END_REF] for agents to perceive their environment. WebSub requires their agent platform to manage a Web server to receive notifications from a WebSub hub (Fig. 1c).

Among the three patterns observed here, only one meets the layered system constraint (Fig. 1b). In the two other patterns, there is no obvious distinction between an agent space and an environment space among system components. Indeed, if one considers an entire system component as an agent, then some hypermedia agents are not strictly situated in some environment (due to the absence of origin servers). Conversely, if one considers any RDF data as being part of the environement, system components mix both agent behavior and environmental resources. The word 'servient' emerged during standardization work on WoT, as the contraction for 'server and client', to characterize such system components [START_REF] Kovatsch | Web of Things (WoT) Architecture. W3C Recommendation[END_REF]. Because of this ambiguity, there is no obvious definitions for perception and action on RDF data in the presence of interaction cycles. In this paper, we intend to bridge that gap through a single abstract formalism that defines perception and actions of agents with respect to a hypermedia environment defined as an RDF dataset. We consider the following requirement: while preserving the usual RDF abstractions used in the Semantic Web literature, our formalism shall capture all MAS architectures, including those involving servients.

Formalism

The main contribution of the paper is a hypermedia MAS formalism, in which the environment and agent spaces are strictly separated, to maximize uncoupling. The formalism we now present will be evaluated in Sec. 4 by showing that existing EMAS prototypes could be re-implemented with equivalent functionalities but with existing W3C standards for representing agent resources (including Linked Data Platforms and ActivityStream, both relying on Semantic Web technologies).

Preliminaries

We start from a classical representation of agency (the ability of agents to act on ther environment) as functions on environmental states and actions, borrowed from Genesereth and Nilsson (chapter 13) [START_REF] Genesereth | Logical Foundations of Artificial Intelligence[END_REF] and Wooldridge (chapter 2.5) [START_REF] Wooldridge | An introduction to multiagent systems[END_REF]. To the best of our knowledge, this representation has remained the most widely known reference to study generic interactions between agents and their environment, without making assumptions on agent architectures.

In the following, we define abstract structures for an environment, an agent and a multi-agent system.

Definition 1 (environment). An environment definition E is a tuple

E = E, e 0 , A, do where -E is a set of states -e 0 ∈ E is an initial state -A is a set of actions -do : A × E → 2 E is

an effectory function

Note that function do maps to subsets of E rather than to elements of E. This choice allows for non-deterministic actions on the environment, as per Wooldridge's definition of E.

Definition 2 (agent). A stateful (or hysteretic) agent definition A is a tuple

A = P, I, i 0 , see, internalize, act where -P is a set of percepts -I is a set of internal states -i 0 ∈ I is an initial internal state -see : E → P is a sensory function -internalize : I × P → I is a memory function -act : I → A is a decision-making function
The definition above includes the basic components of an agent's cognitive loop: the agent perceives its environment, changes its internal state of mind accordingly and then acts. When multiple agent are situated in the same environment, they form a MAS. Definition 3 (system). A multi-agent system definition S is a tuple

S = E, A 1 , A 2 , . . .
where -E is an environment definition every A i is an agent definition Together, agents change the state of their environment over time. We model a MAS run as a sequence of environmental states obtained through agent actions. Agent actions are themselves conditioned by what agents perceive and by their internal state of mind. See Fig. 2a for an overview of how functions are chained during a MAS run.

We now formally define MAS runs. In the following definition, we choose to model time in the most abstract possible way, as a fully ordered set T of time positions-a timeline-with lower bound t min . We denote t -and t + the (unique) predecessor and successor of any point in time t ∈ T . Definition 4 (system run). Let T be a timeline. A sequence e t t∈T of environmental states is a system run for S = E, A 1 , A 2 , . . . if for all t ∈ T e t = e 0 if t = t min e ∈ do(act(i t ), e t -) for some i t , otherwise and if for all t ∈ T and all A i = P, I, i 0 , see, internalize, act

i t = i 0 if t = t min internalize(i t -, see(e t )) otherwise
With this definition, we choose to deal with potentially conflicting actions between agents by assuming that no two actions can be executed at the same time. A MAS can however be defined such that an agent keeps choosing the same action as long as it does not see its effects. As a result, concurrent actions are in fact serialized in an arbitrary order by the environment.

Note that in our definition, i t may be equal to i t -if the two successive environment states are indistinguishable by the agent. In this modeling, perception is instantaneous. An agent always internalizes a state as soon as an action occurs (as soon as function do() is applied). We will see how a hypermedia MAS differs in that respect.

Dataset, Operations

As discussed in Sec. 2, the Web can be seen as a single open environment, which agents browse through hypermedia. A common abstraction for the Web is to see it as an RDF dataset, i.e. as a set of labeled graphs, each identified with a URI [START_REF] Carroll | Named graphs[END_REF]. If nodes of these graphs are themselves URIs, an edge can then be seen as a hyperlink, which agents can follow to discover more data.

This abstraction (which is a formalization of the Linked Data principles) slightly alters the nature of perception by autonomous agents. If everything on the Web is made of URIs, an agent may universally interpret Web resources. URIs are indeed unambiguous. As a result, agent situatedness in a hypermedia environment does not depend on the individual sensory capabilities of agents but rather on the fact they may only retrieve a finite set of resources at a time. In the following, we formally introduce the RDF abstraction for the Web and redefine the function see() in the context of a hypermedia environment.

We first briefly introduce the RDF data model10 : U and L are respectively the set of (internationalized) URI resources and literals. U L = U ∪ L is the set of Web resources. T = U × U × U L is the set of RDF triples. The elements of an RDF triple s, p, o ∈ T are respectively called its subject, its predicate and its object. The set of RDF graphs is G = 2 T . Finally, U × G is the set of named graphs. The first element of a named graph is the name of the RDF graph given as the second element.

An RDF dataset is a set of named graphs. The Web is thus (at a given time) an infinite set of named graphs d = { u 1 , g 1 , u 2 , g 2 , . . .}. When an agent performs a GET request on resource u 1 , what it gets as a response is g 1 . In the definitions to come next, we will use the shorthand notation σ u1 (d) to denote { u 1 , g 1 }. Moreover, we will denote O the set of operations to perform on Web resources. O is defined as {GET, PUT, POST, DELETE} × U × G.

As discussed above, perception in a hypermedia environment consists in retrieving a subset of the Web. We define the set of environmental states as D, the set of all RDF datasets and the set of percepts as the set D ⊂ D of all finite datasets. On this basis, we can now define a standard sensory function on RDF datasets.

In a hypermedia environment, we only consider perception as resulting from link traversal. On the Web, link traversal is initiated by the agent, not by the server, via operations of the form GET, u, ∅ . We denote O GET the set of such operations and define the function transfer :

O GET × D → D such that transfer( GET, u, ∅ , d) = σ u (d)
The name 'transfer' gets its name from the REST architectural principles, which are oriented towards a 'state transfer' from servers to clients.

Similarly to the transfer() function, we can define a standard effectory function based on operations. We define update :

(O \ O GET ) × D → D such that update( PUT, u, g , d) = d \ σ u (d) ∪ { u, g } update( POST, u, g , d) = d ∪ { u, g } update( DELETE, u, g , d) = d \ σ u (d)
This definition, along with that of transfer(), is aligned with the HTTP Graph Store protocol, a W3C standard to manipulate RDF datasets over a REST interface [START_REF] Ogbuji | Sparql 1.1 graph store http protocol[END_REF]. Operations with GET are said to be safe because they never lead to any update in the environment.

While we've considered hyperlinks in the partitioning of D, there is another important aspect of hypermedia that must be properly modeled as well: Web forms. The environment should include forms, i.e. request templates to indicate what operations are permitted in the environment. We can define another function to map the state perceived by the agent to potential actions that the environment offers or, in other words, affords. We define it as afford : D → 2 O .

We now have everything at hand to redefine environments, agents and multiagent systems in a hypermedia context.

Definition 5 (hypermedia environment). A hypermedia environment E h is a tuple

E h = D, d 0 , O, transfer, update, afford
Note that the definition above defines a singleton, in the sense that there exists only a single set D, a single set O, a single function transfer, etc. Only the definition of d 0 could arguably be defined on an application basis.

Definition 6 (hypermedia agent). A hypermedia agent A h is a tuple

S h = E h , A h,1 , A h,2 , . . .

Fig. 2b gives a comparison with generic MAS in terms of function chaining.

The main difference is in the position of the sensory functions transfer() vs. see(). By defining a shared function for perception, agents can all be situated in the same open environment. The downside of the approach is that perception becomes an action on its own: the decision-making function act() outputs both safe operations (for state transfer) and unsafe update operations. Transfer results from a (GET) request/response exchange between an agent and a server. Definition 8 (hypermedia system run). Let T be a timeline. A sequence d t t∈T of datasets is a hypermedia system run for

S h = E h , A h,1 , A h,2 , . . . if for all t ∈ T d t = d 0 if t = t min update(act(i t ), d t -) if act(i t ) ∈ afford(d t -), for some i t
and if for all t ∈ T and all A h,i = I, i 0 , internalize, act

i t =      i 0 if t = t min internalize(i t -, transfer(act(i t -), d t )) if act(i t -) ∈ O GET internalize(i t -, ∅) otherwise
In this modeling, we assume that update() and transfer() are instantaneous. Yet, one cannot build all MAS variants as hypermedia MASs. As discussed in Sec 2, the notion of servient is however sufficient to have an equivalence between classically defined MASs and hypermedia MASs.

Servients

In hypermedia systems, the situatedness of an agent is primarily conditioned by the hypermedia controls (links and forms) it finds in the environment. Hypermedia controls do constrain the perception and action range of the agent. Yet, in the various prototypes we have reviewed in Sec. 2, the perception of agents also depends on another factor: the resources it owns as a Web server. As a servient, an agent has full access to the resources it owns and, in particular, it gets immediately notified whenever these resources are updated (by another agent).

We now incorporate the notion of resource ownership to Def. 6. In the following definition, we use the shorthand notations δ t as the difference d t \ d t - and σ R (d) as the union u∈R σ u (d).

Definition 9 (hypermedia servient). A hypermedia servient A hs is a tuple

A hs = I, i 0 , R, internalize, act where -I, i 0 , transfer, internalize and act are as per Def. 6 -R ⊂ U is a set of resources owned by the agent We also modify Def. 8 accordingly.

Definition 10 (hypermedia system run bis). A sequence d t t∈T of datasets is a hypermedia system run for S hs = E h , A h,1 , A h,2 , . . . , A hs,1 , A hs,2 , . . . if, in addition to constraints of Def. 8, for all A hs,i = I, i 0 , R, internalize, act

i t =      i 0 if t = t min internalize(i t -, transfer(act(i t -), d t ) ∪ σ R (δ t )) if act(i t -) ∈ O GET internalize(i t -, σ R (δ t ))
otherwise

The modification allows us to assert an equivalence between classical MASs and hypermedia MASs, as formally expressed below.

Theorem 1. Let τ : E → D be a bidirectional transformation that maps every arbitrary environmental state (Def. 1) to some RDF dataset (Def 5).

For every multi-agent system S, there is an equivalent hypermedia system S hs . That is, for every run e t t∈T of S, there is an equivalent run τ (e t ) t∈T of S hs . This equivalence only holds if servients are allowed in the hypermedia MAS.

Artifacts

Our formalism for hypermedia MASs is based on a generic abstraction for the Web: the RDF data model. In practice, agents are likely not to recognize all URIs they find in the environment. Rather, they would be programmed to recognize specific Web ontologies, which specify the structure of resources through a vocabulary and the potential actions available on these resources. To that end, the two EMAS prototypes dealing with hypermedia environments [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF][START_REF] Ciortea | Engineering world-wide multi-agent systems with hypermedia[END_REF] make use of the CArtAgO meta-model [START_REF] Ricci | CArtAgO: A framework for prototyping artifactbased environments in MAS[END_REF]: resources e.g. with a certain content type, such as the Hypermedia Application Language (HAL), or a certain data structure, such as RDF triples with a specific vocabulary (EVE), are turned into software objects called 'artifacts', that agents use as proxies to manipulate the origin Web resources.

In the context of a hypermedia environment, it is however not clear whether artifacts should be part of the environment itself (i.e. modeled as resources) or added to the formalism as their own kind of entity. In the former case, the notion would be redundant with that of a Web resource, introducing again a coupling between the environment and agent spaces.

Rather, we make the assumption here that artifacts are 'translators' between datasets and operations, on the one hand, and more idiomatic representations of states and actions, on the other hand. Artifacts would allow any existing agent architecture to be used against a hypermedia environment. Formally, an artifact can be modeled as a function that maps D to a higher-level state space (e.g. a set of predefined beliefs) and a function that maps arbitrary actions (e.g. WoT forms or social actions) to O. To be consistent with how CArtAgO is used in practice, we also make artifacts stateful entities, as follows.

Definition 11 (artifact). An artifact (or proxy) definition is a tuple

P = E , A , I , transfer , update , internalize
where -E is a set of proxy states -A is a set of proxy actions -I is a set of proxy internal states transfer : D → E is a proxy transfer function update : A × I → O is a proxy update function internalize : E × I → I is a proxy memory function An illustration of the above definition is given in Fig. 2c. Our modeling is consistent with the fact that artifacts are not autonomous agents. As proxies, they do not include any act() function. Moreover, artifact definitions are not tied to specific agents, they can apply to all agents sharing the same abstraction of states and actions.

We do not model actual communication channels in our formalism. In practice, the HTTP communication channel is often between an artifact and the environment rather than between the agent and its environment. The simplest artifact for hypermedia agents is a Web client that turns local actions to HTTP requests.

Ontologies for a Hypermedia Environment

In the following, we briefly introduce ontologies relevant for engineering hypermedia MASs (see Table 1 for an overview). This review shows how to re-implement the four EMAS prototypes in a framework including Semantic Web technologies, as per our formalism. To illustrate how artifacts can help integrate existing agent architectures with a hypermedia MAS, we introduce artifact definitions where E and A are sets of AgentSpeak beliefs and actions [START_REF] Bordini | Programming multi-agent systems in AgentSpeak using Jason[END_REF].

Reasoning with Web Ontologies

All Web ontologies (should) follow the RDF Schema and OWL specifications. These specifications provide means to declare a certain vocabulary to use in other RDF graphs, as well as axioms associated with that vocabulary. An OWL artifact could process all ontological definitions for the vocabulary found in an RDF graph, materialize implicit triples stated through axioms and turn the original RDF graph into a set of Prolog/AgentSpeak predicates.

For example, we assume the existence of resource <room> in an environment d such that transfer( GET, <room>, ∅ , d) = { <room>, g 1 } where g 1 = { <room>, rdf:type, brick:Room <room>, brick:partOf, <floor> <floor>, brick:partOf, <building> } If an agent chooses to look up schema axioms defined in the Brick schema, at location brick: 11 , it gets graph g 2 defined as g 2 = { brick:Room, rdf:type, owl:Class , brick:Zone, rdf:type, owl:Class , brick:Room, rdfs:subClassOf, brick:Zone , brick:partOf, rdf:type, owl:ObjectProperty , brick:partOf, rdf:type, owl:TransitiveProperty } After internalizing g 1 and g 2 , an OWL artifact should take into account OWL class and property definitions, as well as the sub-class and transitivity axioms.

It could e.g. return the following predicates for <room> (assuming the artifact's internal state i has already internalized g 2 ): transfer ({ <room>}, g 1 , i ) = {room('room'), partOf('floor', 'building), zone('room'), partOf('room', 'floor'), partOf('room', 'building')} Brick schema is an ontology for the domain of building automation. A Brick representation of a building is e.g. relevant for autonomous agents controlling vacuum cleaning robots navigating in the building, as in the case of the Neato API [START_REF] Collenette | Multi-agent control of industrial robot vacuum cleaners[END_REF]. It is also relevant for building automation systems to locate sensors and actuators in the building. The Building on Linked Data (BOLD) benchmark 12includes various tasks to perform on a simulated building. The BOLD server, exposing the simulation as RDF, closely follows the formalism we introduce in this paper.

Resource Collections

A recurring pattern in hypermedia systems is to use resource collections. This pattern is e.g. used by O'Neill et al. in their Multi-Agent Microservices (MAMS) scenario [START_REF] O'neill | Delivering multi-agent Mi-croServices using CArtAgO[END_REF]. Linked Data Platforms (LDPs) are a recent W3C standard to implement the resource collection pattern. In LDPs, resource collections are called 'containers', as in the following example: LDP is not the only standard to model resource collections. ActivityStream (also part of a Social Web standard) can also be used, for the same result. The following graph is semantically equivalent to g 3 : g 3 = { <coll>, rdf:type, as:Collection , <coll>, as:items, <member1> , <coll>, as:items, <member2> }

Social Activities

LDPs can be used for specific types of container, such as message inboxes. The Linked Data Notification (LDN) specification standardizes how to use inbox containers. LDN and ActivityStream are both part of a series of W3C standards meant for the Social Web 13 , which also includes WebSub. These standards allow for direct agent-to-agent communication without requiring a dedicated communication channel. Instead, messages are placed in and retrieved from the environmnent.

Another EMAS prototype based on JADE included a basic virtual assistant to manage one's agenda. We give below an example from the Activity-Stream standard to represent agendas. The agenda itself is the named graph <agenda>, g 5 and individual events belonging to the agenda are each a resource, for instance <event>, g 5 , where g 5 and g 5 are defined as g 5 = { <agenda>, as:items, <event> , . . .} and g 5 = { <event>, rdf:type, as:Event , <event>, as:name, "Some agenda event" , <event>, as:startTime, "2021-03-05T00:09:00Z" , <event>, as:endTime, "2021-03-05T00:10:00Z" } In this example, the agenda, modeled as a collection of events, offers the same affordances as described in Sec. 4.2. Each event offers further affordances. For instance, an autonomous agent can reschedule an event by removing the original one from the collection with operation DELETE, <event>, ∅ , to then add the rescheduled event to the agenda with a POST operation.

Affordances

Our formalism enforces agents to follow 'affordances' provided by the environment via the function afford(). We now show how Web forms can be embedded in the environment through two ontologies: the Thing Description (TD) ontology (which includes a module for hypermedia controls) and schema.org.

The TD ontology makes affordances explicit by specifying HTTP request templates as RDF triples. For instance, graph g 4 defined as the graph g 4 = { <lamp>, td:hasPropertyAffordance, <status affordance> , <status affordance>, td:forProperty, <status> , <status affordance>, td:hasForm, <status form> <status form>, hctl:hasTarget, <target> <status form>, hctl:forOperationType, td:readProperty } 13 https://www.w3.org/TR/social-web-protocols/ includes one affordance to retrieve the on/off status of a lamp via a GET request:

afford({ <lamp>, g 4 }) = { GET, <target>, ∅ }
The TD ontology defines a small set of operations that are possible on 'things' (physical objects on WoT). A TD artifact could e.g. provide a high-level action for the td:readProperty operation type. This approach has been implemented with JaCaMo [START_REF] Boissier | Multi-agent oriented programming: programming multi-agent systems using JaCaMo[END_REF] for a summer school on Artificial Intelligence for industrial applications 14 . In the JaCaMo implementation, a ThingArtifact object would expose the following action for g 4 : readProperty('lamp', 'status', Value).

As with resource collections, the TD ontology is not the only way to make affordances explicit. The following graph embeds the same affordance as g 4 : g 4 = { <lamp>, schema:potentialAction, <status action> , <status action>, schema:actionStatus, schema:PotentialActionStatus , <status action>, schema:target, <status form> <status form>, schema:httpMethod, "GET" <status form>, schema:urlTemplate, "target" } This graph uses the schema.org vocabulary for actions. The approach is being used in another research project on agents in manufacturing [20]. Moreover, schema.org actions are used by the Alexa virtual assistant, as a target representation of natural language commands [START_REF] Kollar | The alexa meaning representation language[END_REF].

Speech Acts

The MAMS scenario described by O'Neill et al. is based on FIPA's Agent Communication Language (ACL). We show here how to emulate ACL speech acts with ActivityStream.

While WebSub does not recommend a particular vocabulary for the exchanged messages, LDNs and ActivityPub (a third Social Web protocol) encourage using ActivityStream activities. Activities have properties such as actor, target, type, and object. By comparison, ACL messages include the analogous properties 'sender', 'receiver', 'performative' and 'content fields'. Activities could therefore be a substitute for ACL messages on the Social Web. Table 2 gives a mapping from ActivityStream types to ACL communicative acts. Not all ACL speech acts have a correspondance in RDF but the list is enough to implement e.g. an auction, as in the MAMS scenario.

We give an illustration with the first two steps of an auction through LDNs: the auctioneer announces its auction to a bidder with POST, <bidder/inbox>, g 6 , The auctioneer can then accept or reject the offer. Auctioneer and bidder discover each other's inbox through hypermedia, as specified in LDN. Multi-agent protocols can be further specified by using the W3C provenance ontology, PROV-O15 , as suggested by the LDN specification. PROV-O provides a vocabulary to relate activities to entities used or produced by the activity and to agents involved in the activity.

Conclusion

In this paper, we introduced a formalism for hypermedia MASs based on the abstraction that the Web is equivalent to an RDF dataset. We were able to show how four different prototypes recently presented at the EMAS series of workshops could fit our formalism, although none of them uses RDF or other Semantic Web technologies. In addition, we showed how other implementations natively follow the formalism. With this paper, we have aimed at making MAS and Semantic Web technologies converge again, as per the original 2000 vision of autonomous agents on the Web. Because it is based on Semantic Web technologies, our formalism should allow for a scalable hypermedia environment, hosting many (physical or simulated) resources and responding to many agents in parallel. Experimental proof of the scalability of such an environment is yet to be provided, though. Implementation effort could be targeted towards designing reusable artifacts for W3C standards, such as LDPs, ActivityStream and the TD ontology. More importantly, however, what remains to be proven is the ability of agents of different origins of interacting in the same (unknown) environment. The BOLD benchmark is an attempt to tend towards that goal. Other MAS competitions around hypermedia environments could be developed as well.

Fig. 1 :

 1 Fig. 1: Graphical representation of agent interactions on the Web; rounded rectangles are components, circles are component connectors (S: server, C: client) [7]; hatched components are purely reactive components

A

  h = I, i 0 , internalize, act where -I, i 0 are as per Def. 2 internalize : I × D → I is a memory function (on RDF datasets) act : I → O is a decision-making function (with respect to operations) Definition 7. A hypermedia multi-agent system definition S h is a tuple

g 3 =

 3 { <coll>, rdf:type, ldp:BasicContainer , <coll>, ldp:contains, <member1> , <coll>, ldp:contains, <member2> } LDP containers come with implicit affordances, e.g. to add a new item to the collection: afford( <coll>, g 3 ) = { POST, <coll>, g | g ∈ G} An LDP artifact could implement the specification and provide an action to AgentSpeak agents of the form add('coll', Item, ItemId) for all instances of ldp:BasicContainer it would have internalized.

  Integration of a non-hypermedia agent into a hypermedia MAS via an artifact

Fig. 2 :

 2 Fig.2: Graphical representation of abstract (hypermedia) multi-agent systems; rectangles contain function names, circles contain set names, dashed rectangles are REST components (as presented in Fig.1) and dotted rectangles are reusable software modules

Table 1 :

 1 Ontologies relevant for hypermedia MASs

	Name	Namespace URL	Prefix
	Brick schema	http://brickschema.org/	brick:
	Hypermedia Controls	https://www.w3.org/2019/wot/hypermedia# hctl:
	Thing Description (TD)	https://www.w3.org/2019/wot/td#	td:
	Schema.org	http://schema.org/	schema:
	Linked Data Platform (LDP) https://www.w3.org/ns/ldp#	ldp:
	ActivityStream	https://www.w3.org/ns/activitystreams#	as:

Table 2 :

 2 Mapping from ActivityStream to FIPA ACL

	Activity type (ActivityStream) Comunicative act (FIPA ACL)
	as:Announce	Inform, Call for Proposal
	as:Offer	Propose
	as:Question	Request
	as:Accept	Accept Proposal
	as:Reject	Reject Proposal, Refuse
	as:Follow	Subscribe
	as:Undo	Cancel

where g 6 = { <announce>, rdf:type, as:Announce , <announce>, as:name, "Some announcement" , <announce>, as:actor, <auctioneer> , <announce>, as:target, <bidder> , <announce>, as:object, <auction> } to which the bidder submits the offer with POST, <auctioneer/inbox>, g 6 , where g 6 = { <bid>, rdf:type, as:Offer , <bid>, as:inReplyTo, <announce> , <bid>, as:name, "Some offer" , <bid>, as:actor, <bidder> , <bid>, as:target, <auctioneer> , <bid>, as:object, <offer> }

originally about dogs, from a Peter Steiner cartoon published in The New Yorker in 1993.

https://www.hyperagents.org/

https://www.dagstuhl.de/21072

we leave out 'blank nodes' in our definitions, for the sake of clarity.

we represent URIs either as relative URIs or as 'compact URIs' (prefix followed by local name).

https://github.com/bold-benchmark/

https://gitlab.emse.fr/ai4industry/hackathon/

http://www.w3.org/ns/prov#

https://www.w3.org/WoT/ 6 https


Jing Liu

Mathieu Abel

Nian Lin

On-surface Synthesis: A New Route Realizing Single-Layer Conjugated Metal-Organic Structures

Recently, both experimental and theoretical advances have demonstrated that two-dimensional conjugated metal-organic frameworks (2D-cMOFs) exhibit interesting electronic and magnetic properties, such as high conductivity and ferromagnetism. Theoretical studies have predicted that exotic quantum states, including topological insulating states and superconductivity, emerge in some 2D-MOFs. The high design tunability of MOFs' structure and composition provides great opportunities to realize these structures. However, most of conventional synthesis methods yield multi-layer structures of the 2D-cMOFs, in which the predicted exotic quantum phases are often quenched due to inter-layer interactions. It is highly desirable to synthesize single-layer cMOFs.

On-surface synthesis represents a novel strategy towards this goal. In this Perspective, we discuss the recent developments in on-surface synthesis of 1D-and 2D-cMOFs.

Metal-organic frameworks (MOFs) represent a class of functional materials for wide range applications including gas and energy storage, filtration, catalysis, and sensing owing to their versatile structural and functional properties. [START_REF] Stavila | MOF-Based Electronic and Opto-Electronic Devices[END_REF][2][START_REF] Kreno | Metal-Organic Framework Materials as Chemical Sensors[END_REF][START_REF] Hendon | Grand Challenges and Future Opportunities for Metal-Organic Frameworks[END_REF] From the structure point of view, MOFs are considered crystals that comprise lattices of metal atoms and molecules. The structural and compositional tunability of MOFs provides an appealing playground for designing specific lattices. Majority of MOFs features poor electric conductivity because the coordination bonds normally feature weak electronic coupling which does not provide effective hopping between the neighboring sites. This problem can be overcome when coordination modes render aromaticity or quasi-aromaticity. [START_REF] Sun | Electrically Conductive Porous Metal-Organic Frameworks[END_REF] It has been found that a tetra-coordinated square-planar bis-(di-X)M coordination satisfies this requirement. As shown in Scheme 1, a metal ion M and two di-X ligands (X=thiol, hydroxyl, amino) constitute two inter-connected five-member rings. The electronic coupling between the π orbital of the di-X ligands and the d orbital of the metal ion delocalizes the π electrons over the two five-member rings, offering efficient π-conjugation, namely, quasi-aromaticity. This type of coordination yields so-called conjugated MOFs. [START_REF] Kambe | π-Conjugated Nickel Bis(dithiolene) Complex Nanosheet[END_REF] 2D-cMOFs represents a new family of 2D crystals that are uniquely different from inorganic 2D materials such as graphene or boron nitride which are not easily to be functionalized, or 2D organic polymers that are lack of good crystalline.

Scheme 1 On-surface synthesis of single-layer 2D-cMOFs based on bis-(di-X)M coordination (X=thiol, hydroxyl, amino).

Research on 2D-cMOFs prior to 2012 has been mostly focused on structural analysis rather than on their physical properties. Recently, more and more breakthroughs have been made reporting electrochemical activity, photoactivity, semiconductivity, high electrical conductivity and ferromagnetism in 2D-cMOFs. [START_REF] Sakamoto | Coordination Nanosheets (CONASHs): Strategies, Structures and Functions[END_REF][8][START_REF] Huang | A Two-Dimensional π-d Conjugated Coordination Polymer with Extremely High Electrical Conductivity and Ambipolar Transport Behaviour[END_REF][START_REF] Clough | Metallic Conductivity in a Two-Dimensional Cobalt Dithiolene Metal-Organic Framework[END_REF][START_REF] Lahiri | Hexaaminobenzene as a Building Block for a Family of 2D Coordination Polymers[END_REF][START_REF] Campbell | Cu 3 (hexaiminotriphenylene) 2 : An Electrically Conductive 2D Metal-Organic Framework for Chemiresistive Sensing[END_REF][START_REF] Kambe | Redox Control and High Conductivity of Nickel Bis(dithiolene) Complex π-Nanosheet: A Potential Organic Two-Dimensional Topological Insulator[END_REF][START_REF] Pal | Interfacial Synthesis of Electrically Conducting Palladium Bis(dithiolene) Complex Nanosheet[END_REF][15] Remarkably, conductivity of up to 1580 S cm -1 was obtained in the 15-500 nm thick films of a Cu-BHT MOF. [START_REF] Huang | A Two-Dimensional π-d Conjugated Coordination Polymer with Extremely High Electrical Conductivity and Ambipolar Transport Behaviour[END_REF] This high conductivity is attributed to the strong π-d interaction between the metal ions and ligands and to the delocalized electrons in the 2D system. More excitingly, this material was reported to be a single-layer superconductor. [START_REF] Zhang | Theoretical Discovery of a Superconducting Two-Dimensional Metal-Organic Framework[END_REF]17 Another interesting example is a 2D-cMOF exhibiting ferromagnetic ordering below ~20 K. [START_REF] Dong | A Coronene-Based Semiconducting Two-Dimensional Metal-Organic Framework with Ferromagnetic Behavior[END_REF] Concurrent with these experimental advances, theoretical investigations have progressed rapidly. The work of Feng Liu's group, leading to the prediction of the existence of organic topological materials in a series of publications, [START_REF] Wang | Organic Topological Insulators in Organometallic Lattices[END_REF][START_REF] Liu | Flat Chern Band in a Two-Dimensional Organometallic Framework[END_REF][START_REF] Wang | Quantum Anomalous Hall Effect in 2D Organic Topological Insulators[END_REF][START_REF] Zhang | Tunable Topological States in Electron-Doped HTT-Pt[END_REF][START_REF] Jiang | Exotic Topological Bands and Quantum States in Metal-Organic and Covalent-Organic Frameworks[END_REF] is an exciting development. The 2D-cMOFs with bis-(di-X)M coordination have received wide interest. For example, a bis(dithiolato)Mn 2D-MOF was predicted to be a ferromagnetic spin-lattice with S = 3/2. [START_REF] Zhao | Half-Metallicity of a Kagome Spin Lattice: The Case of a Manganese Bis-dithiolene Monolayer[END_REF] The spins in the unit cell form long-range ferromagnetic ordering mediated by p-d hybridization resulting from the πconjugated Kagome lattice. Octaaminonaphthalene-M (M=Fe, Cr, or Co) 2D-MOFs were reported to exhibit half-metallic nature resulting in remarkable 100% spin-filtering efficiency. [START_REF] Li | High Temperature Ferromagnetism in π-Conjugated Two-Dimensional Metal-Organic Frameworks[END_REF] Hexaiminotriphenylene Ni or Cu (Ni-HATP or Cu-HATP) 2D-MOFs display metallic band structures. Zhou et al. showed that d 8 transition metals (Pt and Pd) induce spin orbit coupling (SOC) gaps and the gaps of the NH coordinated complexes are much larger than their amino counterparts. [START_REF] Zhou | Topological Insulators Based on 2D Shape-Persistent Organic Ligand Complexes[END_REF] These predicted physical properties of the single-layer systems are often different in the multi-layer structures in which the inter-layer interactions in the stacked layers may quench the exotic quantum phases. It is thus highly desirable to synthesize single-layer 2D-cMOFs.

However, traditional hydro-/solvothermal methods yield crystalline powders of 2D-cMOFs. [START_REF] Li | Conductive MOFs[END_REF] The interface-assisted synthesis methods, including gas-liquid and liquid-liquid interfacial synthesis, Langmuir-Blodgett (LB) method, solid-liquid interfacial synthesis, are used for synthesizing films and layers of 2D-cMOFs whose thickness ranges from 1-2 μm to 10 nm. To date, only one work reported by Feng's group successfully fabricated a single layer 2D-cMOF which features thickness of ∼0.7 nm using the LB method. [START_REF] Dong | Large-Area, Free-Standing, Two-Dimensional Supramolecular Polymer Single-Layer Sheets for Highly Efficient Electrocatalytic Hydrogen Evolution[END_REF] On-surface synthesis provides a unique approach for fabricating single-layer metal-organic structures. As illustrated in Scheme 1, the linker molecules functionalized with specific chemical groups and metal atoms are deposited on an atomic flat surface, and after annealing at an appropriate temperature, single-layer 2D-MOFs form on the surface. This method has yielded a large variety of 2D-MOFs comprising hexagonal, triangular, square, Kagome, or other complex lattices of metal atoms. [START_REF] Dong | Self-Assembly of Metal-Organic Coordination Structures on Surfaces[END_REF] The whole process normally is conducted in ultra-high vacuum conditions, which enable the state-of-art microscopic and spectroscopic characterizations in further steps. In this perspective, we will discuss the recent progresses in the design, synthesis and characterization of single-layer 1D-and 2D-cMOF structures using the on-surface synthesis.

We will exemplify several combined experimental and theoretical studies concerning (1) the electronic structures, and (2) the magnetic properties of the on-surface synthesized single-layer 1D-and 2D-cMOFs to highlight the advances in the field.

In recent years, on-surface synthesis has emerged as a remarkable strategy to create and isolate single layer of organized 1D-cMOF chains using the surface as a template to drive the assembly and to catalyze the reactions. Benzene-based molecules have been used to react with metal atoms (Scheme 2). [START_REF] Koudia | On-Surface Synthesis of Covalent Coordination Polymers on Micrometer Scale[END_REF][START_REF] Denawi | On-Surface Synthesis of Spin Crossover Polymeric Chains[END_REF][START_REF] Denawi | Magnetic Polymer Chains of Iron and Zwitterionic Quinoidal Ligands on the Ag(111) Surface[END_REF][START_REF] Denawi | Magnetic Polymer Chains of Transition Metal Atoms and Zwitterionic Quinone[END_REF][START_REF] Denawi | Electronic and Magnetic Properties of Metal-Organic Polymers with 4d and 5d-Transition Metal Ions[END_REF][START_REF] Liu | Collective Spin Manipulation in Antiferroelastic Spin-Crossover Metallo-Supramolecular Chains[END_REF][START_REF] Liu | Lattice-Directed Stabilization of Different Spin-State Phases in Metallo-Supramolecular Chains on Au Surfaces[END_REF][START_REF] Santhini | 1D Coordination π-d Conjugated Polymers with Distinct Structures Defined by the Choice of the Transition Metal: Towards a New Class of Antiaromatic Macrocycles[END_REF] All these molecules are based on a phenyl ring with four radicals: i) a zwitterionic quinone (ZQ) functionalized by 2 amine groups and two carboxylic groups, ii) tetrahydroxy benzene (THB) and iii) 2,5 diamino-1,4benzoquinonediimines (2HQDI). The formation of 1D-cMOFs from these molecules proceeds by successive deprotonation/metalation steps in which two covalent bonds and two coordinative bonds are formed between the metal center and two adjacent molecules. This provides a metal oxidation state +II and a full delocalization of the π electrons. The presence of metal centers regularly spaced in the conductive chain is very promising to introduce magnetic properties in the 1D-cMOF. Strictly 1D-cMOFs (nanowires) are fascinating from fundamental and applied points of views. [START_REF] Bose | Quantum Communication through an Unmodulated Spin Chain[END_REF] While non-covalent metal-organic coordination chains are well documented, [START_REF] Messina | Direct Observation of Chiral Metal-Organic Complexes Assembled on a Cu(100) Surface[END_REF][START_REF] Lin | Real-Time Single-Molecule Imaging of the Formation and Dynamics of Coordination Compounds[END_REF] covalent links (i.e., with preservation of conjugation) between metal and organic molecules to form cMOFs have just emerged. [START_REF] Kezilebieke | Hierarchy of Chemical Bonding in the Synthesis of Fe-Phthalocyanine on Metal Surfaces: A Local Spectroscopy Approach[END_REF][START_REF] Kezilebieke | Steric and Electronic Selectivity in the Synthesis of Fe-1,2,4,5-Tetracyanobenzene (TCNB) Complexes on Au(111): From Topological Confinement to Bond Formation[END_REF][START_REF] Koudia | Step-by-Step on-Surface Synthesis: From Manganese Phthalocyanines to Their Polymeric Form[END_REF][START_REF] Sakamoto | The Coordination Nanosheet (CONASH)[END_REF][START_REF] Kambe | π-Conjugated Nickel Bis(Dithiolene) Complex Nanosheet[END_REF][START_REF] Nardi | On-Surface Reaction between Tetracarbonitrile-Functionalized Molecules and Copper Atoms[END_REF] Due to the growth process used so far, the extension of these nanowires is often limited. To overcome this limitation, reactive growth process was used involving ZQ and iron atoms co-deposition on a Ag(111) substrate held at 200 °C (Figure 1a-d).

The reaction proceeds by successive deprotonation/metalation steps and finally wires in which each quinoid unit is linked to the metal center by two covalent and two coordinative bonds through N and O atoms, thereby producing a π electrons delocalized over the entire 1D-cMOF. This is confirmed by X-ray photoelectron spectroscopy (XPS) experiments and allows the formation of micrometer size 1D-cMOF. [START_REF] Koudia | On-Surface Synthesis of Covalent Coordination Polymers on Micrometer Scale[END_REF] In this case the distance between two molecules is measured to be 7.6 Å in a (√7x √7) R20° superstructure. This lattice parameter is found very close to the equilibrium lattice parameter calculated by DFT when intermediate spin state is considered for each Fe atoms (S = 1). When this ZQ-Fe cMOF is deposited on Au(110), the lattice parameter is enlarged to 8.2 Å due to a c(4x2) epitaxial relationship measured by LEED (Figure 1e-h). Such a large lattice parameter comparing to the one obtained on Ag(111) (7.6 Å) cannot be interpreted without taking into account a spin crossover (SCO) phenomenon where the spin state of Fe atom change from S = 1 to S = 2 and the associated equilibrium lattice changes from 15.4 Å to 15.9 Å (i.e., 7.7 Å and 7.95 Å between adjacent molecules) (Figure 1i). 31 1D-cMOF (Product 3) comprising 2HQDI and metal atoms (M = Cr, Fe, Co, Ni) are formed on Au(111) and Cu(111). [START_REF] Santhini | 1D Coordination π-d Conjugated Polymers with Distinct Structures Defined by the Choice of the Transition Metal: Towards a New Class of Antiaromatic Macrocycles[END_REF] A combination of XPS, STM, nc-AFM, and DFT calculations was used to characterize in (Figure 1j), demonstrating that all metal atoms adopt a fourfold coordination motif with the nitrogen atoms after dehydrogenation of the 2HQDI molecules providing a full delocalization of the π-d electron system over the entire 1D-cMOF. In contrast, complexation between Cu adatoms and 2HDQI molecules on Cu(111), a different configuration of the metal is obtained, in which 2-fold coordination of Cu atoms preventing the full delocalization of the electron density over the nanowire. [START_REF] Santhini | 1D Coordination π-d Conjugated Polymers with Distinct Structures Defined by the Choice of the Transition Metal: Towards a New Class of Antiaromatic Macrocycles[END_REF] Transition metal complexes with 4 to 7 d electrons can adopt different spin configurations either high-spin, intermediate-spin and low-spin depending on ligand field splitting, and SCO has been observed under external stimuli such as light, pressure temperature or electric field. [START_REF] Hauser | Ligand Field Theoretical Considerations[END_REF] The on-surface synthesis of 1D-cMOF has allowed a description and manipulation of individual spin state at the atomic level. As presented above in the case of ZQ-Fe 1D-cMOF, the epitaxial relationship between the spin chain and the substrate can be used to strain the molecular wire forcing it to change spin state from S = 1 to S = 2 (Figure 2). This phenomena in 1D-cMOF chains of THB and Ni atoms synthesized on different Au substrates [Au(111), Au(110) and Au(100)] are studied using STM, STS under magnetic field and DFT calculations. [START_REF] Liu | Lattice-Directed Stabilization of Different Spin-State Phases in Metallo-Supramolecular Chains on Au Surfaces[END_REF] Distinct STM topographies of the 1D-cMOFs are observed on the three Au surfaces (Figure 2a). [START_REF] Liu | Lattice-Directed Stabilization of Different Spin-State Phases in Metallo-Supramolecular Chains on Au Surfaces[END_REF] Specifically, a collective SCO in the 1D-cMOF chains prepared on Au(111) is demonstrated using tip excitations. [START_REF] Liu | Collective Spin Manipulation in Antiferroelastic Spin-Crossover Metallo-Supramolecular Chains[END_REF] By applying voltage pulses, the brightness of multiple Ni atoms in the same coordination chain, which representing their spin states, are found to switch collectively (Figure 2d ande). Such collective conversions lead to the reversible switching between two degenerate states of the chain, that is, the transition between the spin-state configurations of "...101010..." and "...010101..." in the chain.

The realization of single-layer 2D-cMOFs by on-surface synthesis has been explored using benzene-or triphenylene-derived ligands with ortho-disubstituted N-, O-, or S-containing functional groups (Scheme 3a), [START_REF] Sun | Electrically Conductive Porous Metal-Organic Frameworks[END_REF][START_REF] Li | Conductive MOFs[END_REF][START_REF] Maeda | Coordination Programming of Two-Dimensional Metal Complex Frameworks[END_REF][START_REF] Ko | Conductive Two-Dimensional Metal-Organic Frameworks as Multifunctional Materials[END_REF] including metal-organic oligomers (Products 1 and 4 in Scheme 3b) via the coordination between 2,3,6,7,10,11-hexaaminotriphenylene (HATP, Scheme 3a) and Cu or Ni on Cu(111), [START_REF] Lischka | Competitive Metal Coordination of Hexaaminotriphenylene on Cu(111) by Intrinsic Copper Versus Extrinsic Nickel Adatoms[END_REF] 2D thiolate coordination networks of Ag 3 (C 6 S 6 ) (Product 4 in Scheme 3b), Cu 6 (C 6 S 6 ) (Product 5 in Scheme 3b), and Cu 8 (C 6 S 6 ) (Product 6 in Scheme 3b), on Ag(111) and Cu(111), using benzenehexathiol (BHT, Scheme 3a), [START_REF] Meng | Tunable Thiolate Coordination Networks on Metal Surfaces[END_REF] 2D networks with Ag 3 and Cu 3 clusters embedded (Product 2 in Scheme 3b) using hexahydroxytriphenylene (HHTP, Scheme 3a) molecules on Ag(111) and Cu(111), respectively, [START_REF] Rochefort | Role of the Structure and Reactivity of Cu and Ag Surfaces in the Formation of a 2D Metal-Hexahydroxytriphenylene Network[END_REF] and extended 2D-cMOFs, of Cu 3 (C 6 O 6 ) (Product 3 in Scheme 3b) on Cu(111) [START_REF] Zhang | On-Surface Synthesis of a Semiconducting 2D Metal-Organic Framework Cu 3 (C 6 O 6 ) Exhibiting Dispersive Electronic Bands[END_REF] and Fe 3 (C 6 O 6 ) (Product 4 in Scheme 3b) on Au(111) [START_REF] Hua | Highly Degenerate Ground States in a Frustrated Antiferromagnetic Kagome Lattice in a Two-Dimensional Metal-Organic Framework[END_REF] using benzenehexol (BHO, Scheme 3a), Ni 3 (HITP) 2 (HITP: 2,3,6,7,10,11hexaiminotriphenylene) [START_REF] Gao | Synthesis and Characterization of a Single-Layer Conjugated Metal-Organic Structure Featuring a Non-Trivial Topological Gap[END_REF] and Fe 3 (HITP) 2 [START_REF] Gao | Design and Synthesis of a Single-Layer Ferromagnetic Metal-Organic Framework with Topological Nontrivial Gaps[END_REF] (both are Product 4 in Scheme 3b) on Au(111) using HATP. The combined STM and XPS studies in these works demonstrate the deprotonation of the molecular ligands, indicating that the deprotonated coordination reactions (Scheme 3b) are responsible for the formation of the metal-organic products on the surfaces. [START_REF] Lischka | Competitive Metal Coordination of Hexaaminotriphenylene on Cu(111) by Intrinsic Copper Versus Extrinsic Nickel Adatoms[END_REF][START_REF] Meng | Tunable Thiolate Coordination Networks on Metal Surfaces[END_REF][START_REF] Zhang | On-Surface Synthesis of a Semiconducting 2D Metal-Organic Framework Cu 3 (C 6 O 6 ) Exhibiting Dispersive Electronic Bands[END_REF][START_REF] Hua | Highly Degenerate Ground States in a Frustrated Antiferromagnetic Kagome Lattice in a Two-Dimensional Metal-Organic Framework[END_REF] Moreover, it's found in these studies that the careful control over the substrate-adlayer interactions and metal-organic interactions is crucial for the achievement of extended 2D metal-organic structures with high quality. A 2D-cMOF (Product 3 in Scheme 3b) is synthesized by the dehydrogenated coordination reaction between benzenehexol (BHO, Scheme 3a) and the Cu adatoms on Cu(111). [START_REF] Zhang | On-Surface Synthesis of a Semiconducting 2D Metal-Organic Framework Cu 3 (C 6 O 6 ) Exhibiting Dispersive Electronic Bands[END_REF] The STM topograph and DFT-optimized model of the Cu 3 (C 6 O 6 ) monolayer are displayed in Figure 3a and b, respectively. Theoretical investigations reveal the band structures of the freestanding (Figure 3c) and surface adsorbed (Figure 3d) Cu 3 (C 6 O 6 ), respectively. It can be clearly seen in Figure 3c that a highly dispersive band with a band width of 1 eV and an effective mass of 0.45 m e appears above 2.7 eV. In addition, there are two narrow bands near the Fermi level, giving rise to a direct band gap at Γ point of 2.2 eV. Comparison between Figure 3c andd The dispersive bands were also found in the Ni 3 (HITP) 2 monolayer on Au(111) achieved by the on-surface dehydrogenated coordination (Scheme 3b, Product 4) between HATP (Scheme 3a) and Ni. [START_REF] Gao | Synthesis and Characterization of a Single-Layer Conjugated Metal-Organic Structure Featuring a Non-Trivial Topological Gap[END_REF] 3i), and the gap is retained in the adsorbed monolayer (black dots in Figure 3i). These theoretical results provide evidence of a non-trivial topological gap in the absorbed Ni 3 (HITP) 2 monolayer.

A series of extended 2D-MOFs exhibiting magnetic coupling were achieved by on-surface coordination chemistry. [START_REF] Tseng | Two-Dimensional Metal-Organic Coordination Networks of Mn-7,7,8,8-Tetracyanoquinodimethane Assembled on Cu(100): Structural, Electronic, and Magnetic Properties[END_REF][START_REF] Umbach | Ferromagnetic Coupling of Mononuclear Fe Centers in a Self-Assembled Metal-Organic Network on Au(111)[END_REF][START_REF] Abdurakhmanova | Superexchange-Mediated Ferromagnetic Coupling in Two-Dimensional Ni-TCNQ Networks on Metal Surfaces[END_REF][START_REF] Faraggi | Modeling Ferro-and Antiferromagnetic Interactions in Metal-Organic Coordination Networks[END_REF][START_REF] Giovanelli | Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-Based Metal-Organic Networks[END_REF] Combined STM and X-ray magnetic circular dichroism (XMCD) investigations of these 2D-MOFs reveal either ferro-or antiferromagnetic interactions between the 3d-metal centers, which were ascribed to the super-exchange coupling via the molecular ligands. [START_REF] Umbach | Ferromagnetic Coupling of Mononuclear Fe Centers in a Self-Assembled Metal-Organic Network on Au(111)[END_REF][START_REF] Abdurakhmanova | Superexchange-Mediated Ferromagnetic Coupling in Two-Dimensional Ni-TCNQ Networks on Metal Surfaces[END_REF][START_REF] Faraggi | Modeling Ferro-and Antiferromagnetic Interactions in Metal-Organic Coordination Networks[END_REF] In all these cases, conjugated organic ligands [e.g., 7,7,8,8tetracyanoquinodimethane, 68,70,71 1,2,4,5-tetracyanobenzene, [START_REF] Giovanelli | Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-Based Metal-Organic Networks[END_REF] and 2,4,6-tris(4-pyridyl)-1,3,5triazine 69 ] were used. It is in line with the theoretical study by Bellini et al. [START_REF] Bellini | Propagation of Spin Information at the Supramolecular Scale through Heteroaromatic Linkers[END_REF] concluding that efficient conjugation through the organic linkers in the metal-organic hybrids can enhance the super-exchange coupling between the metal centers. In this context, 2D-cMOFs provide a playground for constructing various 2D magnetic orderings and exploring the related physics.

An example of the study addressing the magnetic coupling in an on-surface synthesized 2D-cMOF, Fe 3 (HITP) 2 . [START_REF] Gao | Design and Synthesis of a Single-Layer Ferromagnetic Metal-Organic Framework with Topological Nontrivial Gaps[END_REF] Theoretical exploration of the freestanding Fe 3 (HITP) 2 monolayer (Figure 4b) demonstrates a ferromagnetic ground state (Figure 4c) in which each Fe center possesses a net out-of-plane magnetic moment of 2.45 μ B . The experimental realization of the single-layer Fe 3 (HITP) 2 framework was achieved by dehydrogenated coordination (Scheme 3b, Product 4) of Fe and HATP (Scheme 3a) on Au(111). STM topograph of Fe 3 (HITP) 2 on Au(111) (Figure 4a)

shows a similar hexagonal framework with that of Ni 3 (HITP) 2 , in which the Fe atoms are arranged in a Kagome lattice, in agreement with the theoretical models. STS measurements show a V-shape feature around the Fermi level which can be attributed to either the Kondo effect or the spin excitations (Figure 4d). The dI/dV map at 8 mV provides a direct look at the spatial distribution of the V-shape resonance in the spectra. It can be seen in Figure 4e that the dim regions induced by the V-shape spectral feature are mainly localized at the Fe centers, which is consistent with the calculated spin density distribution, indicating the presence of a magnetic moment at the Kagome lattice of Fe atoms. In addition, the theoretical exploration also indicates this 2D-MOF structure as a promising candidate of a quantum anomalous Hall system Copyright 2021 American Chemical Society.

A frustrated antiferromagnetic Kagome lattice is formed in a single-layer 2D-cMOF (Scheme 3b, Product 4) formed by BHO (Scheme 3a, denoting dehydrogenated BHO as BHO -6H

hereafter) and Fe on Au(111). [START_REF] Hua | Highly Degenerate Ground States in a Frustrated Antiferromagnetic Kagome Lattice in a Two-Dimensional Metal-Organic Framework[END_REF] Combined STM, XPS and DFT investigations reveal a stoichiometry of Fe 3 (BHO -6H ) of the 2D framework which comprises a Kagome lattice of Fe atoms at a high-spin state of S = 2 (Figure 4f andg). In order to elucidate the magnetic ground state of the Fe 3 (BHO -6H ) framework, the authors theoretically tested several magnetic configurations, including out-of-plane ferromagnetic, out-of-plane ferrimagnetic, in-plane ferrimagnetic, and in-plane antiferromagnetic. Consequently, it is found that the most energyfavorable configuration comprises the in-plane antiferromagnetically coupled Fe centers. Further calculations of several different in-plane antiferromagnetic configurations (Figure 4h), that is, A (also known as the q = 0 state of the Kagome lattice [START_REF] Grohol | Spin Chirality on a Two-Dimensional Frustrated Lattice[END_REF][START_REF] Chernyshev | Quantum Selection of Order in an XXZ Antiferromagnet on a Kagome Lattice[END_REF] ), B, C and D (also known as the q = √3 × √3 state of the Kagome lattice [START_REF] Grohol | Spin Chirality on a Two-Dimensional Frustrated Lattice[END_REF][START_REF] Chernyshev | Quantum Selection of Order in an XXZ Antiferromagnet on a Kagome Lattice[END_REF] ), uncover their comparable energies, suggesting them as degenerate ground states. A representative dI/dV spectrum shows two steps at ±6 mV (Figure 4i).

The conductance steps were assigned to spin excitation caused by either magnetic anisotropy or a spin gap. The spatial resolved dI/dV spectra acquired along the dotted line in Figure 4j shows that the step feature associated with the spin excitation is a global effect taking place in the entire framework while appears stronger at the Fe atoms. This result likely indicates a spin gap as the origin of the spin excitation.

The concept of on-surface synthesis has been well demonstrated for designing and fabricating 1D-and 2D-cMOF structures. Though only being demonstrated in limited examples, this method already shows promising potentials to realize single-layer 1D-and 2D-cMOFs.

Future developments of employing this method to fabricate free-standing single-layer 1D-and 2D-cMOFs or grow 1D-and 2D-cMOFs on decoupling layer are of great importance in order to investigate and harvest their intrinsic electronic and magnetic properties.

Acknowledgement: This work is supported financially by Hong Kong RGC 16301219.

Scheme 2

 2 Scheme 2 Schematic illustration of the 1D coordination reactions used for the synthesis of 1D-

Figure 1

 1 Figure 1 (a,b) STM images of ZQ co-deposited with Fe on Ag(111) with alignment of 1D chains

  On Au(100) [Au(110)], most Ni atoms in the chains are darker (brighter) than the molecular moieties, while on Au(111), darker and brighter Ni atoms arrange alternately along the chains. High resolution STS measurements reveal the different spin states of the brighter and darker Ni atoms. The dI/dV spectra acquired at the brighter Ni atoms on Au(110) and Au(111) feature zerobias anomalies which are attributed to the Kondo resonance of the spin electrons localized on the Ni atoms (Figure 2b). As a comparison, the darker Ni atoms on Au(100) and Au(111) show featureless spectra around the Fermi level, indicating the absence of Kondo effect. The experimental results are in accordance with the DFT calculations demonstrating an S = 1 (high spin, HS) state of the brighter Ni atoms on Au(110) and Au(111) while an S = 0 (low spin, LS) state of the darker Ni atoms on Au(100) and Au(111). Different spin-state phases of the 1D-cMOFs are identified on the three Au surfaces, that is, a LS phase on Au(100), a HS phase on Au(110), and an antiferroelastic (AFE) phase with alternately arranged HS-and LS-Ni atoms along the chains on Au(111) (Figure 2a).

Figure 2 .

 2 Figure 2. (a) STM images of the coordination chains formed by THB and Ni on Au(100) (left),

51 , 53 Scheme 3

 51533 Scheme 3 (a) Chemical structures of the molecular ligands used for preparation of 2D-cMOFs on

  (the contribution from the MOF is drawn in thick black lines) shows that despite the down-shifted positions of the bands and the narrowed band gap of the absorbed Cu 3 (C 6 O 6 ) monolayer, the main band characteristics of the freestanding structure, especially the dispersive conduction band, are preserved upon its adsorption on Cu(111). Further atom-specific analysis uncovers that the dispersive band is dominantly contributed by the , and orbitals of Cu, and the + orbitals of O. The coupling between these d, p orbitals with in-plane components results in a π-like nature of the conduction band and hence an in-plane conjugation of the O-Cu-O bonding motif. The latter was believed to be the origin of the dispersive conduction band. The theoretical results were confirmed by the experimental measurements. The power spectral map of Cu 3 (C 6 O 6 ) (Figure 3e) enables direct observation of the dispersive conduction band above 0.8 V and the narrow bands at negative bias with a 1.5 V band gap between them. The larger experimental band gap in comparison with the calculated results was attributed to the underestimation of band gap in the DFT method.

Figure 3

 3 Figure 3 (a) STM image of Cu 3 (C 6 O 6 ) on Cu(111). (b) Theoretically optimized model of the

Ni 3 (

 3 Figure 3c and d) Ni 3 (HITP) 2 monolayers. It's clearly seen in Figure 3h that the intrinsic band

Figure 4

 4 Figure 4 (a) High-resolution STM image of the single-layer Fe 3 (HITP) 2 on Au(111). (b) DFT-


Myriam Lewkowicz

q=Futureproofing:%20Making%20Practice-Based%20IT%20Design%20Sustainable&cc=fr&lang=en Strategic Thinking for Sustainable Practice-Centered Computing

This book was a trigger for me to reflect on all the projects we have conducted at the local, regional, national, and European levels around healthcare, addressing the social isolation of elderlies, the social support among caregivers, and the coordination issues of professionals willing to take care for patients at their home. Since Ina Wagner interviewed me in Paris, the situation evolved in France as a new healthcare law was voted that emphasizes the importance of cooperation among healthcare practitioners, the need for IT support, and the key role of local territories (which is not obvious in France, that is a very centralized country). The reflection that started with this book definitely helped me to make decisions in this evolving context, and I am grateful to Claudia Müller who, through an interview, facilitated me to realize what are, from my experience, the main issues that have to be dealt with when aiming at ensuring a sustainable practice-based computing approach. In this epilogue, I briefly list and illustrate these main issues, hoping they could support other sustainable experiences.

Following topics

One of the most important and obvious thing to do is to identify research questions that are independent of a case, and to ensure that projects can ensure a follow-up of these research questions. For instance, I studied knotworking (Engeström, 2008) with Khuloud Abou Amsha in different settings. In PiCADO, a three years long inter-ministerial funded project, we studied the collaborative practices of self-employed healthcare professionals (self-employed workers in charge of the economics of their practice: general practitioners, nurses, speech-language pathologists, physiotherapists, occupational therapists, dieticians, etc. ) taking care of patients at home (Abou [START_REF] Abou Amsha | Chapter 3-Supporting Collaboration to Preserve the Quality of Life of Patients at Home-A Design Case Study[END_REF]. In HADex, a one year long regionally funded project, we studied the coordination among salaried healthcare professionals of the "hospitalat-home" organization. Finally, in CALIPSO, a two years long regionally funded project, we studied the coordination between the different healthcare actors for the whole trajectory of a patient, from hospital to home, and vice versa, addressing the sharing of information and the communication between two very different healthcare systems (at least in France): in the city and at the hospital (Berthou, tbp.). By adopting the design case study framework [START_REF] Wulf | Engaging with practices : Design case studies as a research framework in CSCW[END_REF], we were able to develop a conceptual reflection on knotworking and how to design to support it (Abou [START_REF] Abou Amsha | Computer-Supported Knotworking Design guidelines based on two case studies from the healthcare domain in Europe[END_REF], reflection that led us to develop a discourse towards the local and regional healthcare actors in France so that our research could impact local communities.

Getting political support

Having an impact on local communities is one important aspect of socio-informatics that we embrace, ensuring that the research questions that we tackle are those that are "important, meaningful, and impactful for the communities" with whom we are working (Hayes, 2018 p. 308). Created by decree of September 14, 1994, the Troyes University of Technology was born out of a strong political will. The general council of Aube -and more precisely its president, Senator Philippe Adnot -bet on technological development and innovation to save the economy of the department, highly industrialized (fourth French department) but suffering from the crisis in the textile and the mechanical industries [START_REF] Moraux | Université de Technologie de Troyes[END_REF]. This favorable political context encouraged us to interact regularly with the Senator, who then became aware of the research we were conducting, and convinced by the positive impact it could have for citizens, local companies, students, and research groups. He and his team then regularly invited us to lunches at the Senat to introduce us to major actors of companies in the healthcare sector (insurances, IT, transportation), envisioning our research as a way to attract diverse economic players in the department. He also invited us to national events, and discussed policies debated in the French Senat. This political support has definitely opened us prospects and given me a complementary vision that was very useful in making strategic decisions.

Being flexible

Something that I have learnt after fifteen years of research within healthcare is that flexibility, in the sense of being able to adapt and to change strategies as the context evolves, is another important aspect of sustainability. I will illustrate this aspect with our journey through a major evolution of our ecosystem.

When we defined the CALIPSO project as a follow-up project of PiCADO, our objective was to build up upon CARE [START_REF] Amsha | CARE : An Application to Support the Collective Management of Patients at Home[END_REF], the prototype that was developed to support knotworking. For so doing, we involved a local (based in Troyes) software company that was used to work with the local hospital in the project. The goal was both to deliver a robust product, and to ensure its maintenance, which would ensure the sustainability of the whole approach. However, this initial plan was disrupted.

The disruption started with the French territorial reform in 2016 that reduced the number of regions from 22 to 13. Before this reform, our research group was one of the few working on coordination among healthcare practitioners in our region (Champagne-Ardenne). The new region, called Grand-Est, includes Lorraine and Alsace, two previous regions on their own, that contain major research centers, big hospitals, and well organized associations. A regional agency, named Pulsy, was created to be the preferred operator of the Grand-Est Regional Health Agency for the development and implementation of the regional e-health strategy. It aims first at supporting and promoting the use of digital health services in the territories to health professionals, health establishments, social and medico-social structures, and users. Its objective is also to facilitate the sharing and exchange of data, in a standardized and secure framework, to coordinate care and life paths, to support its members in the implementation of regulatory obligations and standards of good practice, and to promote innovation and territorial initiatives in the field of e-health (www.pulsy.fr). Pulsy therefore proposes a catalog of systems and related services that interferes with potential local developments. Indeed, in the French healthcare system, a hospital cannot fully decide which information systems they may use; if they decide to use a system that is not "prescribed" by its Regional Health Agency, they are not financially supported for its acquisition, its customization, nor its deployment.

We were then confronted to a difficult situation: should we go on working with the local software company, but end up with a system that fits our research results but that would not be deployed by the local hospital anymore… We faced a dilemma, as supporting a practicecentered approach at the regional level would mean losing the system that we contributed developing during two design case studies. Keeping in mind a long-term perspective, we decided not to fight against the regional e-health agency and to accompany the national strategy, applied at the local level. The decision was not easy, as the software company was also at risk of losing an important market, leading to economic lay-off. The system that was supposed to be developed during CALIPSO was then never finished, but we are now involved with the local hospital in the deployment of Parcéo, a system supported by Pulsy that calls it "the whats app for the nurses and the doctors". By making the point that we have an expertise in this domain, we managed to be integrated into the project and to have a say in the customization and the deployment process. A PhD student from our research group (paid by the university) is now following the whole process, aiming at pushing in favor of a practicecentered point of view.

Ensuring independence through diverse sources of funding

Another important aspect of sustainability is to balance the financial and the intellectual independence. After fifteen years of responding to calls for projects, I have now learnt to adopt a portfolio approach, mixing short and longer projects, funded by companies or administrations (hospital, healthcare agencies), and by public authorities. Indeed, public funding ensures intellectual independence but also means more bureaucracy, more time spent on deliverables (and less on writing manuscripts), whereas direct contracting with companies or administration means money that can be spent exactly as we want (without having to respect a budget plan defined three or four years ago). I adopt the same approach for funding PhD; it is interesting to have a company funding a PhD (in France there is a financial incentive scheme) as the company becomes interested in the success of the research, the PhD student gains an employment experience, and the research group is financially supported for the supervision of the student. On the other hand, it becomes more difficult to ensure fully critical thinking in this framework. Therefore, it is important to decide which topic to address under which framework.

For instance, in the new context, it is crucial to start interacting closely with Pulsy, the new ehealth regional agency presented above. I have then joined forces with a colleague based in Strasbourg (where the headquarters of Pulsy are) and negotiated a PhD there, who is going to work on the regional version of the national e-health strategy. However, as mentioned above, when following the deployment of Parcéo (the system supposed to support the cooperation among all the care actors), it is important to ensure that a publicly funded PhD student is working on the case. It guarantees that we will be able to raise concerns about the system and its deployment and publish about that.

Postponing and pausing activities

Even if following topics is an important factor for sustainability, that we mentioned first, it goes with being able to postpone and pause activities. Indeed, what is important is to keep track of open research questions, and to be opportunistic when deciding to address them.

For instance, we started to work on teleconsultation in 2015, as both the head of the emergency medical dispatch center in Troyes, and the head of a company offering a telemedicine toolkit contacted us to assess the deployment of this telemedicine toolkit in ten nursing homes. While conducting this assessment, we got interesting findings [START_REF] Gaglio | It is Not Because You Have Tools that You Must use Them » : The Difficult Domestication of a Telemedicine Toolkit to Manage Emergencies in Nursing Homes[END_REF], but did not have time to explore them in detail, partly because our sociologist colleague who led the study, Gérald Gaglio, got a full professor position in another university. However, In Section IV, Epilogue of: SIMONE, Carla, WAGNER, Ina, MÜLLER, Claudia, et al. Future-proofing: Making Practice-Based IT Design Sustainable. Oxford University Press, 2022, pp.341-347. https://global.oup.com/academic/product/future-proofing-9780198862505?q=Futureproofing:%20Making%20Practice-Based%20IT%20Design%20Sustainable&cc=fr&lang=en I kept that in mind, and when in 2019, I got some funding through one of the sponsors of the SilverTech Chair of our university, I took this opportunity to reopen the topic; I went back to the doctor in charge of putting in place teleconsultation between the local hospital and nursing homes. I offered him to welcome a master student to study what they have put in place, which he accepted. The study [START_REF] Cormi | How the local domestication of a teleconsultation solution is influenced by the adoption of a national policy[END_REF] really interested the hospital, which Director decided to hire the student for a PhD.

Building a team

The last but not least sustainability aspect is related to hiring the right people and networking them with the local and regional institutions. Indeed, what was key in the development of our research in the last ten years was the possibility to hire two assistant professors, Matthieu Tixier first, in 2013, and Khuloud Abou Amsha four years after. Historically, and until shortly, they both would work with me, but not with each other. So, when I had the occasion to reopen the teleconsultation topic as described above, I offered them to supervise the student together. It went well, and I supported them by interacting with the head of the hospital when they were defining the PhD project for the master student that they are now supervising together.

I envisioned my role as a mentor, positioning them on some topics, supporting them finding the funding, and let them grow, while being present if they need any advice. By this strategy, I can also share the responsibility with Khuloud and Matthieu and I do not have to carry everything by myself; having more people involved at the university is definitely a matter of sustainability.

We have also recently hired an assistant professor in management science, Loubna Echajari, conducting research related to crisis management in industry. As the pandemic started, she asked if I could put her in contact with the hospital. I did so, asking them if they were interested by a study that our research group would fund. They accepted, her presence and her work [START_REF] Sanchez | L'évolution des routines comme levier de l'innovation organisationnelle : Le cas du Département d'Information Médicale du Centre Hospitalier de Troyes face à la crise Covid-19[END_REF] were really appreciated, which played an important role in how the hospital is seeing our research group as highly pertinent, compared to the other research groups from our university they are working with (related to optimization and data management).

Conclusion

Finally, looking back at fifteen years of research applied in the healthcare domain conducted at the Troyes University of Technology, trying to have a positive impact on patients, their informal caregivers, and the professionals, I would say that the strategy that has been developed and followed is aligned on the strategy that was envisioned in 1994, when the University was created thanks to the strong political will of Senator Philippe Adnot. All the activities described in chapter 5, analyzed in chapter 11, and reflected in this epilogue demonstrate some of the "lived practices" in executing this overall strategy. Through these activities, we took part in the development of the local associations and in the positioning of the local hospital, and there is more to come. Indeed, last year, the department has been chosen as one of the five departments in France (that counts 101 departments) to experiment what has been called "population responsibility". It corresponds to the "triple aim" approach put in place in North America

In Section IV, Epilogue of: SIMONE, Carla, WAGNER, Ina, MÜLLER, Claudia, et al. Future-proofing: Making Practice-Based IT Design Sustainable. Oxford University Press, 2022, pp.341-347. https://global.oup.com/academic/product/future-proofing-9780198862505?q=Futureproofing:%20Making%20Practice-Based%20IT%20Design%20Sustainable&cc=fr&lang=en [START_REF] Berwick | The Triple Aim : Care, Health, And Cost[END_REF]: a better care experience for the patient, a better health for the population, and a lower cost for society. It also involves going beyond city-hospital oppositions, and focusing on prevention. By taking part in this initiative that entails ambitious improvement at all levels of the healthcare system, we are pursuing our strategy in favor of sustainable practice-centered computing that, as we have showed, must be envisioned as a local cooperative endeavor, with all its struggles, but also new kinds of opportunities.

  In Section IV, Epilogue of: SIMONE, Carla, WAGNER, Ina,MÜLLER, Claudia, et al. Future-proofing: Making Practice-Based IT Design Sustainable. Oxford University Press, 2022, pp.341-347. https://global.oup.com/academic/product/future-proofing-9780198862505?q=Futureproofing:%20Making%20Practice-Based%20IT%20Design%20Sustainable&cc=fr&lang=en