Abdelkader Gouaich
email: gouaich@lirmm.fr

Coordination and conversation protocols in open multi-agent systems

Introduction

Technological evolutions achieved in several computing fields such as hardware, networking and software engineering have enlarged the potential use of software-based services. Hence, current and future software systems are expected to be communicative and collaborative systems defined everywhere and offering their services at anytime to help users in their daily activities. Still, both changes on expectations and technological evolutions have also implied changes on software systems properties and hypothesis previously formulated on them. Hence, current and future software systems exhibit the following properties [START_REF] Zambonelli | Signs of a revolution in computer science and software engineering[END_REF] :

-Situatedness: Having local communication and local interaction properties, a software system's global functionality depends on the local context of its elementary components. -Openness: The software system has no longer a defined clear barrier and static structure. It is permanently evolving by merging or rejecting sub-components. -Locality in interaction: Interaction among components can be conducted locally without requiring a centralised communication infrastructure. This raises the dynamics of the software system and allows emergence of new observable functionalities defined by elementary components. -Heterogeneity: Obviously in a large connected world several actors with different goals build software components. Hence, several heterogeneous entities have to collaborate or coordinate their actions when placed together in a certain context in order to achieve their local goals. -Autonomy of the components: Autonomy of a software component is an important feature that should be remembered when designing large open distributed software systems. Hence, software components have to be considered as black boxes, and lack of knowledge on their internal structure make them behaving autonomously since their reaction to an external stimulus is not fully predictable [START_REF] Gouaich Abdelkader | Requirements for achieving software agents autonomy and defining their responsibility[END_REF].

In this context, agent-based software engineering offers an interesting approach for designing and building this class of software systems. In fact, most of the presented features have already been considered as axioms in the theoretical foundation and definition of the agency [START_REF] Wooldridge | Intelligent agents: theory and practice[END_REF][START_REF] Ferber | Les Systemes Multi-Agents[END_REF]. This paper focuses on coordination and conversation aspects of multi-agent systems and tries to make a formal link between coordination protocols and their related conversation protocols.

Autonomy and Responsibility of software agents

An autonomous software agent is defined as a self-governed entity that decide what action to do according to its local goals and rules [START_REF] Castelfranchi | Guarantees for autonomy in cognitive agent architecture[END_REF]. Starting from this autonomy interpretation and by considering communication and interaction as another fundamental feature of software agents, [START_REF] Gouaich Abdelkader | Requirements for achieving software agents autonomy and defining their responsibility[END_REF] has established the need of an automatic entity that does not modify its internal rules to achieve actual interactions among autonomous agents.

In fact, the integrity of the software structure encoding the agent's computational behaviours was found as a sine qua none condition in order to implement autonomous agents without having any assumption on their internal architecture. So, to interact an agent is not allowed to modify other agents' software structure and delegate this risky action to a trusted automatic entity, namely the deployment environment. On the other hand, in order to meet requirements of autonomous agents and guarantee virtual agent society norms on coordination and conversation, it was found useful to consider the multi-agent system as a composition of two orthogonal components: autonomous agents and the deployment environment [START_REF] Gouaich Abdelkader | Requirements for achieving software agents autonomy and defining their responsibility[END_REF]. Autonomous agents are considered as unknown software components that interact in order to achieve their private goals. The term unknown refers to software components that hide completely the software structure implementing their behaviours. As seen above, this feature has to be considered as an axiom in large distributed systems. Besides, the deployment environment may encode the agent virtual society laws and norms independently from agents that populate it and thus establishes a referential to establish agents responsibility. For instance, interaction and conversation policies may be implemented by this entity. Since, the deployment environment is an automatic entity its internal laws are static and identifiable. Due to this property, the responsibility of the deployed unknown autonomous agents is established when their actions challenge the norms of the agent virtual society [START_REF] Gouaich Abdelkader | Requirements for achieving software agents autonomy and defining their responsibility[END_REF]. As an example of such deployment environment an algebraic model named MIC* has been introduced in [START_REF] Abdelkader | Mic * : An agent formal environment[END_REF].

{Movement, Interaction, Computation}* (MIC*):

MIC* is an algebraic structure where autonomous, mobile and interacting entities are deployed. Within this framework, all interactions are conducted by explicitly exchanging interaction objects through interaction spaces. Hence, agents do not alter directly the deployment environment or the perceptions of other agents, but send their attempts as interaction objects. Interaction objects are structured: in fact, a formal addition law can compose them commutatively + to represent simultaneous interactions. Furthermore, abstract empty interaction object 0 can be defined to represent no interaction.

The less intuitive part of the structure of the interaction objects concerns negative interaction objects. Negative interaction objects are constructed formally and may have no interpretation in the real world. However, they are useful for the internal model definitions and implementation of the deployment environment. For instance, the deployment environment can cancel any action, x, of the agent simply by performing an algebraic operation, x + (-x) = 0, that is expressed within the model notations. Finally, interaction objects defines a structure of a commutative group (O, +), where O represents the set of interaction objects and + the composition law. Interaction spaces, represented by S, are defined as abstract locations where interaction between agents holds. They are active entities that control their local and specific interaction rules. For instance, interaction object that are sent inside an interaction space may be altered if they violate the interaction norm. Agents, represented by A, are autonomous entities that perceive interaction objects and react to them by sending other interaction objects. As said before, agents' actions are always considered as attempts to influence the deployment environment structure. These attempts are committed only when they are coherent with the deployment environmental rules of evolution. Having these elementary definitions, each MIC * term is represented by the following matrices:

-Outboxes Matrix: The rows of this matrix represent agents A i ∈ A and the columns represent the interaction spaces S j ∈ S. Each element of the matrix o (i,j) ∈ O is the representation of the agent A i in the interaction space S j . -Inboxes Matrix: The rows of this matrix represent agents A i ∈ A and the columns represent the interaction spaces S j ∈ S. Each element of the matrix o (i,j) ∈ O defines how the agent A i perceives the universe in the interaction space S j . -Memories vector: Agents A i ∈ A represent the rows of the vector. Each element m i is an abstraction of the internal memory of the agent A i . Except the existence of such element that is proved using the Turing machine model, no further assumptions are made in MIC * about the internal architecture of the agent.

The set of all MIC* terms is represented by T .

Dynamics of MIC*:

The dynamics of the deployment environment is described as a sequence of elementary evolutions: T → T . Three main classes of evolutions were characterised in MIC*:

-Movement µ: A movement is a transformation µ, of the environment where both inboxes and memories matrices are unchanged, and where outboxes matrix interaction objects are changed but globally invariant. This means that the interaction objects of an agent can change positions in the outboxes matrix and no interaction object is created or lost. -Interaction ϕ: The interaction is characterised by a transformation ϕ that leaves both outboxes and memories matrices unchanged and transforms a row of the inboxes matrix. Thus, interaction is defined as modifying the perceptions of the entities in a particular interaction space. -Computation γ: An observable computation of an entity transforms its representations in the outboxes matrix and the memories vector. For practical reasons, the inboxes of the calculating entity are reset to 0 after the computation to distinguish interaction objects that were involved in different computations. The main idea of MIC* approach is that the dynamics of the deployment environment can be modelled as a composition of evolutions that can be considered as being a movement, interaction or computation. Consequently, as presented in figure 1, any state of the deployment environment can be reached by following a path of evolutions of type µ, ϕ or γ. Hence, the deployment environment dynamics is no more an unknown and chaotic evolution, but a structured sequence of elementary transformation.

t0 ∈ T f 0 ∈γ∪ϕ∪µ -→ t1 = f0(t0) ∈ T f 1 ∈γ∪ϕ∪µ -→ t2 = f1(t1) ∈ T ❀ tn+1 = fn(tn) ∈ T

Background

Generalised study of coordination:

Malone and Crowson in [START_REF] Malone | The interdisciplinary study of coordination[END_REF] have noticed that coordination among autonomous entities is common to several independent fields such as computer science, economics, operational research and organizational theory. Hence, they have tried to study it in a single framework: the coordination theory. According to their definition, coordination is viewed as managing dependencies between activities. Hence, entities coordinate their actions in order to manage dependencies that exist between their activities. As shown in figure 2, Malone and Crowson sketch a categorisation of the dependencies among autonomous entities as follows:

Shared resource: When several activities share some limited resource a particular resource allocation strategy is needed in order to handle this dependency. Several independent fields have identified this dependency and proposed some specific resource allocation strategies. For instance, computer science field has studied how available hardware and software resources are shared among computational entities. Hence, multi-threaded operating systems require allocation strategy and algorithms to share the computation units (processors, input/output devices) on a computer. Another example of limited resource dependency is the optimal sharing of available network bandwidth using a network protocol. Producer/Consumer Relationship: This dependency represents situations when an activity produces something that is used by another activity. This relation implies the following dependencies: Prerequisite constraint: This dependency expresses an order that exists between the producer and the consumer. Transfer: When the producer activity produces something that has to be used by the consumer activity, the produced object has to be transferred from the production point to the consumer point. Managing this dependency involves defining how to transport things between the producer and consumer activities. For instance, in case of software programs where the produced thing is information, the transfer dependency is resolved using communication protocols as a transportation mechanism. Usability: The other dependency implied by producer/consumer relationship is the usability. In fact, the consumer should be able to correctly use the producer's products. Standardisation is a common way to resolve this dependency. Hence, both producer and consumer agree on what are the requirements to consider a product as consumable and try to meet these specifications. Syntax of messages and the semantics of commands are examples of standardisation when transferring information between software entities. Simultaneity Constraint: Some activities are timely constrained, so they have to be executed at the same time (or cannot occur in the same time). This dependency expresses these situations. Semaphores are examples of a mechanism used in computer science to handle synchronised activities. Task/Subtask This relation basically expresses the hierarchical decomposition of an activity in several sub-activities. So, the main activity depends on its sub-activities and finishes when they are completed.

Models and methodologies to specify coordination protocols in software systems:

To express coordination protocols among software components several models and notations have been introduced. This paragraph gives an overview of these models.

Software engineering methodologies:

Usually software engineering methodologies such as MERISE and UML include in their specification model some graphical and textual descriptions to specify coordination of activities to be implemented by software programs. Statecharts: Statecharts [START_REF] Harel | Statecharts: A visual formalism for complex systems[END_REF] is an extension of state transition diagrams with three elements dealing with hierarchy, concurrency and communication. This formalism is used for the specification and design of complex discrete-event systems such as distributed systems and communication protocols. Flowchart: A flowchart system shows the overall structure of a software system by tracing the flow of information, work and by highlighting key processing and decision points. It also includes the physical media on which data are inputted, outputted and stored. Process Algebra: This family of formal models (CSP [START_REF] Hoare | Communicating Sequential Processes[END_REF], CCS [START_REF] Milner | Communication and Concurrency[END_REF], Pi calculus [START_REF] Milner Robin | A calculus for mobile processes, parts 1 and 2[END_REF],

Ambient [START_REF] Cardelli | Abstractions for mobile computation[END_REF], Join calculus [START_REF] Fournet | Le Join-Calcul: Un Calcul Pour la Programmation Repartie et Mobile[END_REF]) implicitly expresses coordination among processes by synchronising communication and actions using algebraic operations. So, coordination mechanisms are implicitly defined in the semantics of the operators and rewriting rules. The observable result is still an ordered execution of the distributed activities. For instance, a Pi-calculus process stops its activity waiting for an incoming message on a named communication channel; when another process sends a message on this named channel, the blocked process continues its execution. This synchronisation operation implicitly defines a partial order relationship among activities and can also be viewed as a producer/consumer relation between processes where messages are the exchanged resources. ical and textual language for the description and specification of the interactions between different components normalised by the (ITU). They are usally used in combination with SDL specifications or used as sequence diagram in UML. MSC denotational semantics is expressed using an adaptation of process algebra formalism. This helps in defining partial order relations between events, such as message exchange and actions, occurring in the system. Another interpretation of MSC denotational semantics is done using graph grammars. High-Level Message Sequence Charts (HMSC): They are considered as formalism to compose MSCs automatons using sequence, parallel and alternative operators. These compositions are given two different semantics within HMSC: strong composition, where all events of a scenario must hold before executing the next scenario; and weak composition where events are executed when possible. Since, MSCs semantics is defined as a partial order between events occurring in a system, the semantics of HMSC is defined as an extension of these partial order relations built following the semantics of the composition operators expressing sequential composition, alternative and iteration. HMSC denotational semantics is expressed using grammar graph that helps in studying some general properties of the system using model-checking techniques and to translate the system specification on other specification languages such as SDL, ESTELLE or Statecharts.

Language of Temporal

Software architectures to implement coordination in software systems:

Coordination (software) community has also defined some coordination architecture implementing generic coordination mechanisms such as synchronisation and producer / consumer relationships. Entities of a coordination architecture are the following: coordinables, representing entities to be coordinated; coordination media, representing the media used to coordinate the entities; and finally coordination laws that define how the coordination media reacts in response to coordinables actions. A survey of coordination architectures can be found in [START_REF] Papadopoulos | Models and technologies for the coordination of internet agents: A survey[END_REF]. It categorises coordination architectures in two main categories:

Data driven In data-driven coordination models, the coordination media is represented by an addressable storage space shared between the coordinables. Thus coordinables interact by storing and retrieving data structures from the shared data space. Besides, the coordination laws define how these data structures are represented, stored and consumed by the coordinables. Control driven In control-driven coordination models, the coordination media is represented by a set of input/output communication ports linking coordinables and enabling their interactions. In order to achieve these interactions, the coordination media considers coordinables as black boxes and check their state changes and events occurring on their communication ports. These events are then propagated to other coordinables following some specific coordination rules with no concern for their internal data and representation

Conversational aspects of coordination:

When coordinables are distributed, coordination is necessarily achieved through communication and interaction. Hence, entities communicate by exchanging messages in order to meet the requirements of their coordination protocol. When observing these exchanged messages among coordinating entities, an external observer remarks that the structure of the conversation, defined as an ordered sequence of messages, is guided by the underlying coordination protocol. Specifying this dialogue structure is known as establishing a conversation protocol. Among formalisms that are used to specify conversation protocols one can find the following: finite state machines (FSM), as in works of [START_REF] Barbuceanu | COOL: A language for describing coordination in multi-agent systems[END_REF][START_REF] Barbuceanu | Conversation oriented programming for agent interaction[END_REF][START_REF] Martial | Coordinating Plans of Autonomous Agents[END_REF]; state transition diagrams (STD), as in works of [START_REF] König | State-based modeling method for multiagent conversation protocols and decision activities[END_REF]; coloured petri nets (CPN), as in works of [START_REF] Cost | Using colored petri nets for conversation modeling[END_REF][START_REF] Fallah-Seghrouchni | Protocol engineering for multi-agent interaction[END_REF].

Discussion

As presented above, several works have studied the coordination problem in computer science. These works can be classified in the following categories:

Activity centric: Works of this category focuse on the activity part of coordination. Hence, their main goal is to know what activity to execute and when to execute it. This category is represented by the models for the specification of coordination protocols presented in §3. By observing the literature it seems that activity centric work, conversational centric works and architecture centric constitute blocks with some synergy among them. Still, there is no established formal link between them. Malone and Crowson coordination theory is a first step to link all these works in a single framework. Hence, this paper starts from their works in order to refine a simple dependency based-coordination model expressing dependencies among activities using a directed graph as mathematical model. Having this refined coordination model some concepts such as role, and role-cut are introduced. Conversation protocols are then defined formally as a sequence of messages recognised by a rewriting grammar. This grammar is defined by the structure of the coordination model.

Simple dependency-based coordination model

Figure 2 presented common dependencies shared by several research fields. This categorisation is very helpful to understand why autonomous entities coordinate their actions. However, since Malone and Crowson seek for generality, they make no precise assumptions on the properties of the addressed system. Besides, some of the presented dependencies are redundant and could be expressed with other dependencies. So, by having more assumptions on the entities to be coordinated, would it be possible to define a more refined model of coordination where all dependencies are canonically expressed? To answer this question, let us first set some hypothesis on the considered systems to be coordinated:

-The considered system is a software system composed of either software or hardware autonomous and interacting components; -The autonomy axiom implies that the internal structure of the entities is never accessible and modified by another entity. Consequently, communication and actions of the entities are asynchronous and explicitly represented as attempts of actions [START_REF] Gouaich Abdelkader | Requirements for achieving software agents autonomy and defining their responsibility[END_REF].

The autonomy axiom prevents also from knowing how entities actually behave and achieve their goals. Only observable aspects of their computation are studied. -Communication among components is represented as an explicit exchange of data, or messages, through a communication medium and the communication process is not assumed to be synchronous.

Under these assumptions, all dependencies presented in figure 2 can be expressed canonically as producer/consumer relationships. For instance, the shared resource dependency is modelled by introducing a resource manager entity that gives authorisation to consumer to access the resource according to a particular resource management strategy. The consumers of the resource and the resource manger are obviously in a producer/consumer dependency. Similarly, simultaneity dependency is expressed as a consumer/producer dependency between a monitor and the concurrent components. Finally, task/sub-tasks dependency is also expressed as a set of producer/consumer dependency between the global task and its sub-activities. Consequently, the refined model of coordination has to express only the consumer/producer dependency with the following elements:

Activities: As said previously, coordination is defined between activities; thus, they have to be explicitly represented in the coordination model. Transferable: According to results presented above, all common dependencies among activities can be considered as producer/consumer dependencies. A producer/consumer dependency induces both a transfer and prerequisite dependency. Notice that prerequisite dependency is also a consumer/producer dependency where the notification is considered as the thing to be transported.

Usability dependency:

According to Malone and Crowson's, each producer/consumer dependency induces a usability dependency. The usability dependency guarantees that the transferable is usable by the consumer after being produced by the producer. Consequently, for each transferable a conformity-checking function should be provided to model the usability dependency. Using Malone and Crowson's terms this function represents the standard resolving the usability dependency between activities. Roles: Functionalities of agents in their artificial society are usually abstracted as roles.

Roles are considered in the refined coordination model in order to situate where the activities are executed during the coordination process.

Given these elements, the coordination model can be represented as a directional graph described as follows:

-Two types of vertices are identified representing activities, graphically symbolised as boxes, and transferables graphically symbolised as circles; -For each transferable node a usability-checking function is associated to check the conformity of the transferable according to the usability convention that was established by the producer and the consumer; -An oriented edge links an activity to a transferable to represent a production of a transferable by that activity and a transferable to an activity to represent a consumption of a transferable by that activity. A dependency relation is then completely defined by having the producer vertex, the transferable and the consumer vertex; -As previously mentioned, a prerequisite dependency among activities is expressed as a producer/consumer dependency with a special notification transferable noted . -The coordination graph can be split in several connected components that are linked by transferable vertexes to represent activities associated with each role.

The above elements are captured more formally by the following definition:

Definition 1.
Let O be a set of interaction objects (or messages), a dependency-based coordination model is defined as a digraph G =< A, N, T, F, V ↑ , V ↓ >. A represents the set of activity nodes. N and T are disjoint sets where elements of i ∈ N are considered as notification nodes and elements t ∈ T are transfer nodes. Arrows of the graph are defined by V ↑ and V ↓ , such as V ↑ : A × (N ∪ T ) and V ↓ : (N ∪ T ) × A represent respectively production and consumption arrows. F = {f t∈T : O → O} is a set of functions that check for each transfer node t ∈ T the conformity of the actual exchanged transferable considered as an interaction object.

When a transfer node is consumed by several activities, this is interpreted as an exclusive choice. Thus, only one activity may be executed after production of the transferable. On the other hand, when an activity produces several transferables, this is interpreted as simultaneous production of resources. Roles decomposition in a dependencybased coordination digraph is viewed as a particular partitioning of the activities in the digraph. Roles have to be independent and should not share activities. In fact, without this property, actual agents implementing these roles may be in conflict on activities and consequently lose their autonomy Definition 2. Having a coordination graph G =< A, N, T, F, V ↑ , V ↓ >, a role decomposition d is a subset of P(A) where:

∀x, y ∈ d, x ∩ y = ∅
Roles decomposition divides the global coordination graph in several sub-graphs. Hence, for each role r in a role decomposition d ⊂ P(A), the associated role sub-graphs are built by including all activities of r and inserting all production and consumption arrows that are inside r. This is more formally defined as follows:

Definition 3. A role sub-graph g r =< A r , N r , T r , F r , V ↑ r , V ↓ r > of a role r found in a decomposition d ⊂ P(A) of a dependency-based coordination digraph G =< A, N, T, F, V ↑ , V ↓ > is defined as follows: A r = r N r = { ∈ N : ∃ a, b ∈ A r , (a, ) ∈ V ↑ ∧ ( , b) ∈ V ↓ } T r = {t ∈ T : ∃ a, b ∈ A r , (a, t) ∈ V ↑ ∧ (t, b) ∈ V ↓ } F r = {f t ∈ F : t ∈ T r } V ↑ r = {(a, t) ∈ V ↑ : (a ∈ A r ) ∧ (t ∈ T r )} V ↓ r = {(t, a) ∈ V ↓ : (a ∈ A r ) ∧ (t ∈ T r )} Role sub-
graphs of a complete decomposition are linked by transferables defining dependencies among these roles. This part of the graph is named a role-cut and represents the glue that makes roles interdependent. Still, notification objects, ∈ N , are considered as a special transferable with a special semantics. For instance, they do not induce a usability dependency between activities and can be implemented inside the same software entity without exchanging an explicit interaction object. So, notification nodes that do not always induce an explicit exchange of messages have not to be present in the role-cut. More formally, a roles-cut is specified as follows: Definition 4. Roles-cut of a dependency-based coordination graph G =< A, N, T, F, V ↑ , V ↓ >, is defined as the minimal set of transferable c ⊂ T that if all its elements x ∈ c were removed along with there related production and consumption vertexes this would produce a digraph with more connected components than the original digraph.

Defining conversation protocol grammar from coordination protocol

Notations: Interaction among autonomous agents has to be explicitly represented. For instance, within the MIC* model, a formal deployment environment of autonomous agents [START_REF] Abdelkader | Mic * : An agent formal environment[END_REF], interaction is conducted through explicit interaction objects represented in the set O. This set owns at least, for the purpose of this paper, a structure of a commutative group. Hence, interaction objects found in O can be summed commutatively with the + law. This operation has not to be misinterpreted with the non-commutative concatenation law . (dot) that will be used in order to generate ordered sequences of messages represented by O * . When there is no ambiguity x.y is simply represented by xy. In this section O * represents the free monoid generated by the interaction object set O with the non-commutative dot law. Intuitively this represents words where the alphabet is interaction object set. Ō represents a marked set of interaction object defined as follows: Ō = {x : x ∈ O}. O is defined as union set of O and Ō. |α| is a simple function defined on O * → O * that retrieves marks from all marked interaction object found in a word α. The function π d : O * → O * , where d ⊂ O is a projection of a word on a subset alphabet. In other words, this operation simply retrieves elements found in the word that are not in the subset alphabet d. For an activity node a ∈ A in the dependency-based coordination graph, a + and a -respectively represent the set of production arrows and the consumption arrows of a. Having these notations, the grammar of the conversation protocol is defined as a rewriting system where the rewriting relation,

R →: O * × O *
, is defined as follows: x messages. So, this defines a partial order relationship between messages. After a reduction, messages that have been used in the left part of a reduction relation are marked to avoid confusions and ambiguities: in fact, this mechanism ensures that the left part of a reduction relation is used once.

U 0 a 1 U 1 a 2 U 2 ...a n U n R → U 0 ā1 U 1 ā2 U 2 ... āi U i U i+1 ...U n ⇒ (( i x=1 |a x |, n x=i+1 |a x |) ∈ R) ∧ (∀j ∈ [1..i], a j / ∈ Ō) (a i ) i∈[1..n] ∈ O
What is missing in the previous definition is the relation R : O×O of simplification rules. This set is constructed from the coordination graph G =< A, N, T, F, V ↑ , V ↓ > as follows:

∀a ∈ A, ( (x,a)∈a - x, (a,x)∈a + x) ∈ R G (1)
Having these definitions, a conversation protocol is defined as the set of message sequences recognised by the grammar defined above. This is expressed more formally as: Definition 5. Let O be the interaction objects set; a conversation protocol P (x0,G) for a dependency-based coordination graph and the axiom x 0 ∈ O * is defined as follows:

U ∈ P (x0,G) ⇐⇒ ∃U ∈ O * : U R ❀ x 0 ∧ |U | = U
The problem with the given definition is that it includes all interaction objects that are exchanged among activities. However, as said before only interaction objects exchanged through a role-cut are observable and interesting to study. So, when defining a conversation protocol for a particular roles-cut the previous definition is expressed as follows: Definition 6. Let O be the interaction objects set; A conversation protocol P (x0,G,d) defined on a role-cut d found in a dependency-based coordination graph G for the axiom x 0 ∈ O * is defined as follows:

U ∈ P (x0,G,d) ⇐⇒ ∃ U ∈ O * : U R ❀ x 0 ∧ |π d (U )| = U
Thus, the projection operation ensures that only interaction objects observable on the role-cut are included in the definition of the conversation protocol. Figure 3 presents a simple coordination protocol among three roles: the client, the service broker and the service provider. This coordination pattern in commonly used in both multi-agent systems and distributed systems, where the broker links clients to appropriate service providers. When connected to a client, the service provider recursively proposes offers to the client until the later accepts a good offer.

Simple example

Figure 4 represents an abstracted view of the coordination protocol described in figure 3 where the roles, resources and activities are represented by abstract symbols. The roles-cut in this graph is c G = {x, y, z, v, w}. By applying definition of equation 1, the simplification relations set, R G , is calculated and equals to: Having these elements, and by applying definition 6, the conversation protocol observable at the role-cut, c G , among the three roles is fully defined. e 0 is considered as the axiom the conversation protocol. Notice that the definition of the conversation protocol depends only on the role-cut, no matter how many roles are linked by this roles-cut. Let u = xyzvzvzw ∈ O * be an observable conversation between A, B and C at the role-cut. This conversation is a valid conversation. In fact, by considering α 0 α 1 α 1 α 2 , where α 0 = e 0 e 1 xy, α 1 = e 3 e 4 ze 2 ve 1 and α 2 = e 3 e 4 ze 2 w, this sequence can be reduced to the axiom e 0 as follows: and π cG (α 0 α 1 α 1 α 2 ) = u. The interpretation of this conversation is quite simple, after being connected with the service by the broker; the client has refused two offers and accepted the third one. By contrast, when no path is found to reduce a conversation into the axiom, this means that the partial order of messages has been violated and consequently the coordination protocol is not respected. For instance, yxz is an invalid conversation that will not be recognised by the grammar.

α 0 α 1 α 1 α 3 RG → α 0 α 1 α 1 e 3 e 4 z ē2
The presented approach aims to check conformity of agents' conversation according to coordination protocols at the runtime. Hence, the conversation protocols (or interaction protocols) are not represented explicitly like in [START_REF] Endriss | Competent agents and customising protocols[END_REF] but derived from the coordination protocol. The presented model of coordination is based on producer/consumer dependency relationship. The resource dependency model among roles/agents is becoming used even in agent design methodologies like Tropos [START_REF] Henderson-Sellers | Enhancing agent open with concepts used in the tropos methodology[END_REF] and can be assumed to be rich enough to express complex situations founds in multi-agent systems.

Like [START_REF] Endriss | Competent agents and customising protocols[END_REF] we assume that the coordination protocols and consequently the conversation protocols should be public and represents a part of the multi-agent system social norms. However, each agent has a specific internal strategy that steers its behaviour and responses to external stimulus. This assumption constrains us to check conformity of coordination protocol by an external observer: the deployment environment or the coordination media for instance.

The mediated interaction [START_REF] Omicini | Integrating organisation within a mas coordination infrastructure[END_REF][START_REF] Dente | Integrating and orchestrating services upon an agent coordination infrastructure[END_REF] offers the opportunity to observe all actions coming from the autonomous agents and to check their conformity according to the established norms. In our approach, the interaction mediator will be responsible of checking the conformity of an ongoing conversation by applying results of the definition 6. For instance, the next paragraph presents an example of how conversation protocols are checked within the MIC* framework.

Conforming interactions in MIC*:

Functionally, the conversation protocol checker can be considered as a Boolean function f : O * → { , ⊥} taking as argument a sequence of interaction objects o ∈ O * (or a conversation) and returning a value v ∈ { , ⊥}. ⊥ expresses the invalidity of a conversation while expresses its validity. The set of conformity testing functions is noted CF . Using the approach presented in this paper, the conversation protocol checker has to reduce the conversation to the axiom by using the simplification rules obtained from the coordination protocol by applying the definition of equation 1. When the conversation can be reduced to the axiom, the conversation is considered as valid ( ) and invalid otherwise (⊥).

Interactions in MIC* (see §2.1) are defined as special evolutions of the deployment environment that modify the perceptions of agents, according to emissions of other agents in an interaction space. The goal here is to build interaction operations insuring the conformity of interactions. Hence, a conform interaction ϕ f is built by the following application:

ϕ × CF → ϕ (f, g) → f g
where, f g is defined as following:

∀x ∈ O * : f g = f if g(x) = Id if g(x) = ⊥
Id expresses the identity application that does not modify the deployment environment. So, given a standard interaction operation defined on MIC* and a conversation protocol checker, a conform interaction operation is defined on MIC*. This new interaction operation does not modify the deployment environment, when the conservation is invalid, and behaves as the standard interaction operation ϕ otherwise. Consequently, the deployment environment is never modified by invalid interactions and these bogus attempts are transparently rejected and never reach agents' perceptions.

The next step of our work is to offer to the deployment environment concrete solutions and tools to check if a conversation belongs or not to a certain protocol.

Conclusion

This paper has presented an approach in order to link conversation protocols to their corresponding coordination protocols. Hence, the conversation protocol is seen as structured sequences of messages of interaction objects recognised by the rewriting system. This rewriting system is considered as a conversation policy that can be integrated in a coordination architecture such as MIC* in order to validate conversations in a multiagent system. Consequently, future works have to explore how to automatically and iteratively recognise valid conservations by observing messages among the coordinating entities. This will help in implementing reliable multi-agent systems where conversation laws and consequently coordination protocols are guaranteed by a trusted observer, namely the deployment environment, which established a referential for agents responsibility in large open and untrusted software systems.

Fig. 1 .

 1 Fig. 1. Evolution of a MAS deployment environment starting from an initial term t0 until tn+1 by following elementary transformations of type µ, ϕ or γ.

2 .

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Keywords: Globalization, internet, pluri-disciplinarity, noise, saturation, sound, performance

It could be that the Russian composer Dmitri Kourliandski (1976) synthesises various topics of our time. First of all, if the word "contemporary" still applies these days, then something like a globalization of "contemporary" music is pertinent in his case.

More precisely, a new bridge between France and Russia seems to have been built : What some French observers of present day music call the new "saturation of sound", for instance, is apparent in the works of several French composers (Raphael Cendo, Franck Bedrossian, Yann Robin), but also in the works of Kourliandski himself. A new "aesthetic tendency" may be born, perhaps a new "school" (when post-modernity, in first analysis, had caused the decline of every aesthetics or school, every "ism", at least assumed by the composers themselves). But this school, here, may no longer be a national one (like "the 5" of the Russian romanticism, or "the 6" of French neoclassicism) but might appear like a new international one. The end of U.S.R.R., at least, is clearly involved here. A good illustration of this would perhaps be this concerto "for Porsche and orchestra" (Emergency survival guide, 2006) composed by Kourliandski, like a comic (but not only) sign of the new ultra-capitalist views of Eastern Europe.

Introduction

Dmitri Kourliandski, a Russian composer born in 1976, may be called a musician of the "sound as such2 ". A simple blick on of Broken memory's score, for example, shows that the notes (like in this work in particular) can all simply disappear. Only timbres and rhythms (which are more "vague durations" in this case) stay determinant.

However, this phenomenon, since the first style of Ligeti, Xenakis or since the beginning of the Polish school, during the late 1950's, can obviously not be called an invention of the Russian musician. What might seem more original is the treatment of the sound itself (through a quasi systematic saturation). We will see that some kind of "international school" has emerged around this particular technique (involving notably several French composers). The originality, that of a musician from the XXIst century, is precisely bound to this inscription into an international context, into "globalized" concepts (aesthetics and/or techniques). Some works (some of Kourliandski typically) also seem to follow the topics of plastic arts: the words "happening" or "performance" can become musical in his case, far beyond the first conceptions of John Cage during the 1950's, in Black Mountain College. But the new paradigm could be, even more (in the case of Kourliandski and this could make him a real precursor) some kind of new fusion, more organic, between popular interests and avant-garde. Is it the end of any solemnity in art and notably in music?

Saturation

Emergency survival guide contents and represents a style we could consider emblematic in the case of Kourliandski. Only the rhythms seem to stay predominant, and so precisely noted on the score (as they mark the existence of time, of course, and can not be ignored). That is why their writing stays complex and detailed (see for example the wood-wind instruments and the pianos, all written in triple quavers) 3 . The pitches are nothing more than a simple indication of something high, medium or low. The instruments seem to have become percussion instruments, existing mainly for their timbre, like in the project of Ionisation (1928) by Varese (integrally written for percussion instruments, piano and sirens).

Thus, the relative historical importance of the composer might be linked to this "soundism" (even if the aesthetics are not new, the technical ways to re-approach these aesthetics are). Indeed, Makis 4 Solomos, in his recent book From music to sound4 , proves in a quite exhaustive way that the new paradigm of the 20 th century was sound and no longer "music" (as a combination of "notes" more than sounds). Thus, Varese could have been the real "father" of his century, after all. And Adorno, in his famous Philosophy of new music (written in the beginning of the 1940's), confronting mainly Schoenberg and Stravinsky (revolution against restoration), could have ignored the most crucial point, thinking, along with these two great composers, that music was still a pure problem of pitch, a logical of degrees. Thus, the "sound as such", as a paradigm, is not new if we think about Varese, but also about Italian futurism, John Cage, and later the French "musique concrète", soon becoming (during the 1950's) electro-acoustic and finally "acousmatic" music.

The French musicologist Pierre-Albert Castanet, about Kourliandski and some other composers of the same generation, is right to think about a return: the return of some kind of "soundism" in present day music ("le retour du bruitisme dans la musique savante actuelle 5 "). However, something is new in the case of the young Russian composer. The sounds used by Kourliandski, acoustic or electronic (but acoustic in many cases) are often saturated. In this way, the musician tries to explore an new limit (and perhaps the "final" limit, the "absolute" limit) of instrument: the saturated acoustic. In this way, the soundism becomes something more ontological. According to Bastien Gallet (thinking about these new aesthetics and techniques), writing the sentence in big characters to "saturate the letters or the words" and showing better what he claims: "ONLY A SATURATED SOUND CAN KEEP THE TRACE OF THE EVENT IT IS 6 ". In France, the term of "saturationism", or "saturation", is sometimes used to qualify the technique and aesthetics of Kourliandski and others (mainly Franck Bedrossian, Raphael Cendo and perhaps also Yann Robin).

Let's examine directly an example of acoustic saturation in an orchestral work. Objets impossibles 1 was commissioned by the Ensemble Intercontemporain and created in the Cité de la musique (Paris, November 2010). As early as the end of the first bar, the second horn, like many instruments in the most general case, uses saturated sounds as soon as its part appears. The playing mode may seem strange: con sordina but quadruple forte, which creates a new kind of tensed sound, tensed but not loud (because of the mute) 7 . These aesthetics might be called neo-primitivist (which could be a criticism as a state of non-originality) but not in a research of sonic power any more (like it was, notably, in The rite of spring, 1913). The crudity does not have to be connected to an orchestral demonstration of new sonic possibilities. The crudeness is confident in its new technical identity, confident enough to stay instrumental (and not orchestral as a massive process). Franck Bedrossian, using the same kind of technique, explains this new paradigm 8 . In a way, this "microprimitivism" of the XXI st century, quite generalised (in the case of Kourliandski and Bedrossian), can become a new ductile vocabulary (generating forte as much as piano passages) searching for more 7 The composer himself confirms: "Parameters such as piano or forte are in most cases not determined by a dramatic concept, but by the properties of the material and the intensity of the movement: if you brush the palm of your hand against the body of a piano, it is almost impossible to control the intensity of the sound, and so, the produced intensity is not artificial but completely natural". Kourliandski, 2010, p. 82. 8 « Le principe de saturation du timbre affecte les instruments eux-mêmes de façon individuelle.

[…] De cette recherche découlent de nouveaux timbres associés à de nouvelles techniques de jeu pour toutes les familles d'instruments. L'écriture même des symboles musicaux s'en trouve remise en question. Ce qui découle de cette action, ce n'est pas seulement une distorsion instrumentale mais la découverte d'un nouveau territoire sonore » (« The principle of timbre saturation affects the instruments themselves, in an individual way. […] This research generates new timbres associated to new playing technics for all the families of instruments. The writing of symbols itself becomes problematic »). Bedrossian, 2008, p. 34. "economical ways" than those of Stravinsky. The orchestra is perceived to "go out of itself" (without having to play loudly) and more precisely to be going in the territory of other sounds. For some kind of psycho-acoustical reason, electronic sounds can be heard here (with the exception of the percussion instruments and concerning all the other instruments). It is true that this phenomenon of the acoustic world imitating the electronic world was already there at the end of the 1960's, for instance in the end of Continuum by Ligeti (1968) 9 , or even ten years later in John Adams work: Common tones in simple time (1979) 10 . Here however (in the work by Kourliandski), the phenomenon is systematised. It is the complete orchestra (or at least a great part of it) which becomes something else, with another sonic signature, and thus, "comes out of itself", as we had previously noted.

And we can already advance that the problem here is not the end of tonality: that was the work of Schoenberg, already one century before. Further, the question here is the possible end of the orchestra. After that, why not use quite simply all electronic instruments, if the orchestra "kills itself" in approaching them, and considering their heavy ergonomic superiority? We will come back to this problem later.

One could object that the orchestra, and Kourliandski here, are not trying to imitate this "popular" electronic world. But it may not be totally true. This "saturationist" composer is obviously influenced by pop music, by the saturation of electronic guitar, as Bastien Gallet 9 This work, for harpsichord, ends with a global gesture: the pitches get higher and higher and tighter and tighter. Finally, they equalize themselves on the same quickly repeated note. Thus, the human ear is not familiar with a high pitched note very virtuously repeated by the harpsichord. One recognizes some other instrument, or even some "non musical" noise, like a clock alarm. 10 The work starts with long and very resonant string textures. A piano is added, doubling these textures with light and mechanical batteries (very quickly repeated hesitations between to notes of each chord of this postmodernistand thus tonalwork). The obtained texture is close to some kind of combination of sounds, often proposed by the Korg, Yamaha or Roland personal synthesizers which were beginning to appear at this time -the early 1980's).

had already noticed [START_REF] Here | But the works of these two French composers (also said to be saturationist), can often be closely analysed like Kourliandski's: with the same analytic tools[END_REF] . The generation of Kourliandski no longer fears the world of rock music. The concept of seriousness, on one hand, "vulgarity" on the other, are not so much the problem of our young and post-modern world where "everything has the same value", according to Nicolas Bourriaud (and it is noted that the term "postmodern" is increasingly used to characterize the present period) [START_REF] Lochhead | [END_REF] .

That is one of the new phenomena here. Compared to other arts, Contemporary music was late for that. For instance, plastic arts (always pioneers of new aesthetical concepts during the 20 th century) had already wanted to leave the galleries, to make an art "from and for the street". The fear of Adorno and Horkeimer about cultural industry (in Dialectics of reason, 1944) 13 finally became the fear and the distrust (or even contempt) felt by all contemporary music itself, perhaps until the end of the 20 th century.

Globalization

The second main axis of this text is about Kourliandski and the globalization context, Kourliandski "and internet" in particular.

Kourliandki is obviously a musician composing after 1989, in a neocapitalist country. A symptom of this can be seen in his work

Emergency survival guide (2006). It is a concerto "for 2 automobiles and orchestra" (see Emergency survival guide's score and consider the two "soloists", Auto 1 and Auto 2, the two only instruments which are not capable of executing the rapid and complex rhythms written everywhere else) 14 . In fact, for the first performance, in the Biennale of Venice, the automobile (unique) was a Porsche 911, here even with a supplement of ostentation: the superb orange colour of the car.

We could see in the Porsche a criticism, or not, of the new globalized pan-capitalism (this questioncriticism or notis the problem of the young art of our times, according to Nicolas Bourriaud 15 , and also to the French philosopher Alain Badiou) 16 . If it is not entirely a criticism, eitherway it is still a symbol: a flag of the young post-sovietic Russian greed, greed for the world and its caricatured treasures which were before hidden from it. Even if the presence of the orange Porsche were not really a severe criticism, or not even not a touch of humour or grotesque 17 , Kourliandski would finally appear like a composer of the globalized and merchandized world (where every one knows that 14 This point of view could make of Emergency Survival Guide a real anti concerto: virtuosity is forbidden to the soloists in particular. The concept of note (of pitch), is therefore subtly denied: in the ending of any virtuosity. The instrument stays a pure timbre and the "playing" (eventually virtuosic) on this timbre disappears. 15 « Mais un paradoxe s'attache à cette mission historique, qui devra s'effectuer contre cette mise au pas que l'on nomme "globalisation", et non pas dans son sillage… » ("But a paradox is bound to this historic mission, which will have to be against this [pan-capitalism] that one calls globalisation, and not in its following"). Bourriaud, 2009, p. 18. 16 « Tout le problème est de savoir aujourd'hui ce que c'est qu'un art non impérial, c'est bien une question qui est indiscernablement une question politique et une question esthétique. Une des raisons de la difficulté de l'art aujourd'hui est l'extraordinaire faiblesse de l'invention politique contemporaine. L'espace général de résignation dans lequel l'humanité est installée à cet égard, l'absence de projets, de sorte que l'art est toujours tenté de porter un retrait plutôt qu'un projetcela reflète la situation d'ensemble. » ("the question is: what could be a non-imperial art [which means, in the Marxist vocabulary of the maoist philosopher, a non-"democratic-pan-capitalistic" art], it is a politic and an aesthetic question. One of the reasons of the difficulty of art, today, is the extraordinary weakness of the contemporary politic invention. The general phenomenon of resignation, in which humanity is installed about this weakness, the absence of projects, makes that art is always tempted to carry a retreat and more than a project.") Badiou, 2002, p. 27. 17 Makis Solomos, though, clearly sees in the work Happy mill humoristic aesthetics: "Dmitri Kourliandski's music displays a quality that counterbalances the impression of drama: humour. In Happy Mill, an interactive performance for four female performers, the soloists slowly eat chicken nuggets and chips, and drink some coke -the McDonald's children's menu -, while the computer imitates the process of digestion and produces crumbling sounds reduced to powder. The beginning of… pas d'action, with the huge Alp horn, also has elements of derision in it. Or maybe not. Elsewhere, we are not far frome the grotesque." Solomos, 2010, p. 91. the best cars are German and that having a Porsche, from now on, is less vulgar than "fun", specially in the eye of a post-modern "kidult" 18 , etc.), where communication of art seems to be often included in art itself 19 .

The titles of Kourliandski's works are mainly thought up directly in English, the language of this merchandized world, at least the language of "communication of art". Or in French, like this work directly called Objets impossibles I. Being a citizen of the world, or at least of Europe, is not only convenient, it is a necessity, for a Russian contemporary composer, according to the musician himself 20 . But the globalization is upper most in the fact that in a way, Kourliandski belongs to an international "electronic, online" school of music and aesthetics. Because "saturationism", as we already noticed, is also the technique and the aesthetics of three French composers, Raphaël Cendo, Franck Bedrossian and Yann Robin.

Transmissions (2001) for bassoon and electronics, by Franck

Bedrossian, clearly shows the savage saturating technique, probably more widely than any other work of the "group". The work, which we 18 During the 1970's, the psychologist Tony Anatrella was one of the first to stigmatise those "kidults" (contraction of "kids and "adults"). Later, in 1983, another American psychologist, Dan Kiley, imagined his Peter Pan Syndrome (1983). According to Kiley, it would now be the whole occidental society, frightened by the eternal economic crisis and the difficulty of living in general, which would be touched by this syndrome (the child who doesn't want to grow up). Kourliandski, like any other citizen (and specially this young citizen, born in 1976) could also be more or less touched by this phenomenon. See Amblard and Aymès, 2017. 19 For that opinion about contemporary art, for instance, see Foster, 2002. 20 Answering Omer Corlaix (asking "how do you earn your living in Moscow?"): "Europe! At the time of the Soviet Union, a composer was recognized, he had a status. Today, he no longer exists. He can't earn his living with his music but thanks to the lessons he gives. The composers from the time of the Soviet Union still hold the tenured positions in the conservatories. You have to imagine that from 1948 to the disappearance of the Union of Soviet Composers in 1991, that Stalin had founded in 1932, musical life was run by Tikhon Khrennikov (1913-2007), one of Andreï Jdanov's creatures. He was still officially in charge in 2004, three years before his passing away, and he taught at the Moscow Tchaikovsky Conservatory until his death. Still today, almost all the teachers are pupils of Khrennikov, except for some famous personalities such as my professor Leonid Bobylev. At the Saint-Petersburg Conservatory, the teachers are mainly pupils of Shostakovich. In the end, there is no place for musical creation. Of course, there's a lot of money for classical music but not for contemporary music". See Corlaix, 2010, p. 77-78. could call trash, is typical in its capacity of emphasizingperhapsnew affects. These affects might be horror, embarrassment, and sometimes, then, a new kind of monstrous musical grotesque or tragicomic 21 . As Philippe Leroux notes, "in the creative act, Franck Bedrossian attaches little importance to politeness and good manners" (Leroux, 2008, p. 71). And far beyond, as a matter of fact, the word "Monstrosity" is assumed by the composer himself (Bedrossian, 2008). That could be typically a survivaland more: a technical developmentof the most violent primitivism or expressionism (and finally avant-gardism, modernism). Our exergue, written by Bedrossian, shows that the French musician includes his Russian friend and colleague in his own aesthetical branch, as if the concept of avant-garde (typically modernist) would still exist and if Kourliandski would be part of it. In many ways, these composers finally try to make the great modernism survive. The paradox is that, on the one hand, they belong to the 20 th century, thinking about this idea of avant-gardism and radicalism, this "monstrousism" (where even a certain idea of constructivism is assumed by Kourliandski himself) 22 . And on the other hand, on the contrary, they might be part of the rare composers who belong to their century, trying to build something radically new for orchestra and instruments.

This "school" of saturation, as far as it exists, is not a national one (but Darmstadt wasn't either). The new phenomenon might be that this "school" may even not be a "material" one. Kourliandski knows Bedrossian. Thery are friends. But they mostly discuss their ideas, from the beginning, on internet. So, this group of 4 (Cendo,21 Laughing, of course, the listener has to protect himself against this new embarrassingbecause trashmusic. 22 "Because of this visible mechanization and formalization of my creative processes, many try to draw a parallel between my aesthetics and that of the constructivists and formalists of the twenties in the last century. It is actually difficult to dispute those allegations. However, as far as the aesthetics of constructivism is concerned, what applies best in my case is catastrophe constructivism." Kourliandski, 2010, p. 85. See also Solomos, 2010 (title "constructivism"), p. 98-101. Bedrossian, Kourliandski, Robin), is an international group and more, a e-group, an internet group: it is a group of our globalized times: international and online. Kourliandski has also tried to build a more traditionally Russian "groupe of 5". But the latter doesn't really appear on the international scenenot as much as our e-group of 4and it might eventually disappear in the end.

Pluri-disciplinarity.

The idea of this part is the taste, quite up-to-date, for pluridisciplinarity. It's the same taste, or mode, or symptom, that we noticed during this conference (on Thursday night, 6 th September 2013) in Breathing music, by Justé Janulyté, associated to the "air sculptures" of Dovydas Klimavičius. In both cases, we see the obvious influence of the plastic arts of the 1990's. Let's consider Objets impossible 1 again. In fact, the work, after its first performance, has been re-inoculated in a pluri-disciplinary project, including Kourliandski and Abstract Birds, a collective of plastic internet artists (perhaps not at the top of the art market) 23 . "Abstract Birds" could be the name of a Rock and roll band. That is also a sign of our times, beyond the new fusion between popular and more elitist aesthetics 24 : Kourliandski doesn't work with Jeff Koons or Damian Hirst like Stravinsky could only compromise himself with a Ramuz (or better with Picasso), or Schoenberg with Kandinsky. His works can associate themselves with these confidential internet graphists, these Abstract birds: the globalized world of art is today so big that the communication between artists is not assumed by an eventual unified world of arts anymore. The paradox is that our society of ultracommunication is much more inefficient than yesterday, in this way, just because of the number of artists. The communication then appears chaotic and subjective, hazardous.

Kourliandski has also attempted to build real "physical" installations or even happenings. A good example, already quoted, is Happy mill.

A speaker on a stage comments the noises of digestion taped on the belly of people eating some Mac-Donald. The concept of the work is politic like a plastic art work could be: a reflection about consumerism like for instance Cloaca (2000-7) by Wim Delvoye, the famous "shit machine". The criticism (of the pan-capitalist and ultra consumerist world symbolised by Mac-Donald), this time, is more than clear.

But in the end, we could try to make a nuance (or just ask a question), considering a simple musical work, Four states of same (2005). Indeed, It is easy to feel this power of this work, but also its potential limits. The power, mostly in this vocal work, lies in a fact that the animalism, or what Bedrossian called the monstrosity, is efficient of course, obvious, and expressive, a good point perhaps for a non tonal and so-called constructivist work (much more accessible than many other constructivist works of the past: the numerous serialist pieces of the 20 th century). Then, this famous neo-constructivism could have led all the modernisms to their final simplification and comprehension: these saturated sounds. The saturated voice notably seems to figure the vocal grotesque itself, the very centre of humananimal expression. Wouldn't Stravinsky or Varese have not dreamt of finding it? However, a probable limit is hidden in this expressive animalism, which always goes back, again and again, obviously and fatally, to Varese's soundism, to Viennese expressionism, to Stravinsky's primitivism. A hundred years after the Rite of spring, the idea is still that the truth is to be found in the root, in sexuality, in the animal, in wildness. But this "anti-bourgeoise" idea, crucial in its time, the idea of Freud, then of the whole pessimism of the 20 th century, could now be re-discussed.

Let's forget, however, Four states of same. The second limit, for the saturationism in general, is the pertinence of classical instruments and further, of the score itself. If, according to us, Transmissions of Bedrossian may appear like the purest expression of saturation aesthetics, it might also be the absolute limit of what a score could possibly countain. The electronic part seems to build, to write (directly on the CD) almost the entire part of the final result. Does interpretation still have something to do with such a work? The fusion between the worlds of classical music and pop music might be more accomplished than the composer himself, or any contemporary composer could admit25 (because renouncing the classical world would lead also to renouncing the traditional diffusion of contemporary music, which the musician is used to). This "success" (that of a fusion which seems fatal in our times) also leads to a statement which could frighten many contemporary composers: "we don't need orchestras any more".

In the case of Kourliandski, Broken memory's score is also pertinent to this problem. Indeed, one single page incompasses a whole work (and not an extremely short one: the total duration is around 15 minutes, as is written at the end). We clearly understand that the score, in this case, can not deal with any detail. Could one still call it a score? The terms "diagram" or "performance guide" or "intention" might be more appropriate.

However, let's finish with an opinion by Kourliandski. The musician doesn't admit the vaine of the score. But the latter obviously becomes a simple support, and not the work itself: "I am not so much interested in the transformations of sounds resulting from the textual parameterthe changes indicated in the textas in the physical transformations affecting the musicians while they perform. I started by putting the musicians in such situations that their main concern was not so much to control the accuracy of the sound result as to "survive" under the conditions I imposed on them.

This approach has led me to favour rather static and often repetitive compositions whose central issue is not the control of the sound result but the fact that the sound is beyond any control."

Conclusion.

Dmitri Kourliandski is definitively a composer of "noises" and, in fact, of saturated noises. But this might not be the important concept.

The fact that this music could be "objective" (which the young composer not only claims but explains in detail: see again Kourliandski, 2010), could not appear more like the real originality of the works. The performative aspects of Happy mill? The pluridisciplinarity of Objets impossibles 1? It can be doubted. These techniques (saturation) or essays (of imitating the liberty of plastic arts) could only appear like ways. The real paradigm may be more the discovery of a new centre between two worlds: pop music and "great music" and beyond this: popular world (which is no longer ignorance) and culture in general (which is not "bourgeoise" any more). This might be a centre between "serious" culture and "childish" (regressive) ancient so-called "subculture". That is where the titles of the two first operas appear more than emblematic: determining real new aesthetics, not so much "saturated" or "objective" but rather new "democratic" aesthetics of "kidults". Indeed, if Asteroid 62, or Nosferatu are operas, they are operas of a new society where science fiction and films of the Fantastic are no longer reserved for teenagers but adapted to all of society, identified to its own youth.

Fluxus. Kouliandski, who calls himself an "objective musician", could think about himself as an artist in general more like a musician in particular (which could be especially pertinent today, when the plastic artists have also conquered the sonic world). The last aspect that we have emphasized is that Kourliandski (1976), who is still a very young musician, might be called a "kidult composer" also. His interests are as much "classical music" (traditional "bourgeoise" culture) as teenager "subculture", internet, science-fiction, films of the Fantastic, The Second Style or Intonation, mf, 2017); or musical pedagogy (Harmony Explained to Children, mf, 2006). He has also written several novels (like v comme Babel, Balland, 2001 or Noé, mf, 2016).

He conceived and presented a radio program, concerning musical pedagogy, on the cultural French public radio channel "France

  Porsche, etc. His Concerto for to automobiles (the first performance with a Porsche 911), or his operas Asteroid 62 or Nosferatu, the presence of Mac Donald food in the work Happy mill, show this phenomenon. The result may be the birth of new fusion between popular arts and avant-garde. Even if plastic arts had already begun this fusion during the 1960's, music was late in this peculiar aesthetical project. However, Kourliandski enables the emergence of this fusion when the latter might be one of the most important paradigms of our times: the end of any solemnity in music, or in arts, or even in the entire occidental society? About Author. Jacques Amblard (b. 1970) is a musicologist, associate professor at the Aix Marseille Université (France). His publications concern aesthetics, music of the 20 th and the 21 st centuries (for example in his recent books 20 regards on Messiaen, PUP, 2015 or in Micromusique, PUP, 2017); music and intonation, notably in a book about the French contemporary composer Pascal Dusapin (Dusapin.

"Raphael Cendo, Dmitri Kourliandski et moi-même n'avons pas inventé l'idée de saturation, mais cette catégorie me semble importante pour inscrire notre musique dans le monde panoptique actuel. Car nous vivons dans un monde saturé de surveillance. Les réseaux de communication sont de plus en plus surveillés, tandis que les villes sont couvertes de vidéosurveillances."

The composer himself, however, claims the opposite: "The essence to my approach of sound is that I am not interested in sound as such! what I am interested in are the conditions that make sounds appear: the natural physical data, that is to say the musician's physiology, the construction, the material and the physical characteristics of the instrument; the intensity of the musicians' gesture. Sounds are the projection, the outcome of those conditions (« L'essence de mon approche du son, c'est, apparemment, que le son en tant que tel ne m'intéresse pas ! Ce qui m'intéresse, ce sont les conditions physiques du jaillissement de la sonorité : le matériau et les propriétés physiques de la surface des instruments, d'une part, et l'intensité de la gestique des musiciens, de l'autre. Le son est la résultante de ces conditions »).Kourliandski, 2010, p. 44.

See for instance Emergency survival guide, Jobert, 2011, p. 17.

De la musique au son, 2013.

Oral communication.

« SEUL UN SON SATURE EST A MEME DE CONSERVER LA TRACE DE L'EVENEMENT QU'IL EST ».

The work is available on Youtube (checked in january 2013). One could think that Kouliandski's Objets impossibles 1, here, simply turned into a video music, which doesn't make a new kind of pluri-disciplinarity. Here, the abstract numeric images, however, stick on the music, illustrate the music, precisely not the contrary like in the music of most videos. The final work by Kourliandski and Abstract Birds seems more like an installation "music + numeric images" than a video.

About this general inclination for popular interests, one could mention the subject of the two first operas, as simply appears in their titles: the rather popular theme of science fiction in Asteroid 62 and well as thequite also popularnotion of fantastic in Nosferatu.

Once, Bastien Gallet asked Raphael Cendo: "Why do you not compose electronic or electro-acoustic pieces or, in other words, why do you not compose for a material which can be fully saturated?" SeeCendo, 2008, p. 81.

Culture", each week from September 1999 to june 2000. He gave two conferences at the Collège de France in 2007.

Summary.

Dmitri Kouliandski is a composer of "the sound as such". However, this "soundism" is not that of the last century, and finds new aspects, typical of our new globalized world and common to French composers like Franck Bedrossian, Raphaël Cendo and Yann Robin.

All these composers develop aesthetics (and specific techniques) of saturation. They sometimes write books about their precise topics (see Bedrossian, 2008 or Kourliandski, 2010). A new kind of primitivism is born with them. Is history of music simply still going on, with the eternal invention of new modernisms, searching for more and more wild sounds, or are these composers imprisoned in an ancient paradigm of avant-gardism, whereas many others (who clearly assume to be part of our "post-modern" society) could have left that avant-gardism for ever? That which is post-modern in their case, anyway, is the concept of an international "internet" (virtual) school of composers: international aesthetics at the age of globalisation.

Another typical topic of Kourliandski himself (and not Bedrossian or Cendo this time) is the taste for pluri-disciplinarity. We can see in it the influence of the plastic arts more than the legacy of John Cage or of other composers from the XXth century, more or less bound to