Keywords: Heterogeneous VANET, Software Defined Networking, Distributed Controllers, Mobile Multi-Controllers. I Defined Heterogeneous Vehicular Networks: Taxonomy and Architecture 1

Heterogeneous vehicular networks (HetVNets) are a promising approach to meet the various communication requirements of vehicular networks' services using a variety of available access networks. However, due to their inherited characteristics, HetVNets are rigid, difficult to manage and suffer from a lack of programmability, flexibility, and scalability. In this paper, we first highlight the limits of current HetVNet architectures and show what the emerging software-defined networking (SDN) paradigm can bring to overcome these limitations with a focus on some use cases. We also provide a taxonomy of existing software-defined heterogeneous vehicular networks architectures and discuss their limits. Based on that, we continue by proposing a new SDN-based architecture for H e t V N e t . I t i s a c l u s t e r -b a s e d a r c h i t e c t u r e w i t h a s e m icentralized hierarchical control and an efficient fall back recovery mechanism, that functions in both infrastructure-less and infrastructure-based covered vehicular scenarios. Finally, we demonstrate the feasibility and the efficiency of the proposed architecture compared to the related SDN-based HetVNet architectures through simulation results.

INTRODUCTION

Heterogeneous vehicular network (HetVNet) [START_REF] Zheng | Heterogeneous Vehicular Networking: A Survey on Architecture, Challenges, and Solutions[END_REF] is a promising approach that integrates different access networks such as DSRC and cellular networks to reduce the deployment cost, support the large coverage, and meet the various qualityof-service (QoS) communication requirements of vehicular services. However, the efficient management of HetVNets is still a hard task to perform due to the inherited characteristics of vehicular networks such as high mobility, dynamic topology and the intermittent nature of wireless connections. Indeed, current HetVNet architectures suffer from a lack of programmability, flexibility and scalability [START_REF] Ku | Towards software-defined VANET: Architecture and services[END_REF] to efficiently deal with these increasing challenges. Thus, a new open and flexible HetVNet architecture becomes an absolute requirement to allow an efficient utilization of vehicular resources. Software-Defined Networking (SDN) is among the emerging network architecture paradigms in the last few years. Originally designed for wired networks, SDN has known a phenomenal success both in academia and industry. SDN is based on: (i) a physical separation between the control plane and the data plane, and (ii) a logically centralized control and intelligence in a software controller. OpenFlow [START_REF] Mckeown | Openflow: enabling innovation in campus networks[END_REF] is the most utilized standard for the communication between the control plane and data plane. It defines two kinds of networks equipment: OpenFlow controllers, which centralize all the network control functions and OpenFlow vStwichs, which only perform data packet forwarding functions. Each vSwitch has a flow table that contains controller flow entries. The controller handles the vSwitchs by formulating flow rules and installing corresponding entries in the flow table. A secure channel is used to connect the controller and corresponding vSwitchs.

Given the growing popularity of SDN, researchers are increasingly exploring the possibility of integrating SDN in mobile wireless networks and more massively into cellular mobile networks (e.g., 4G/5G). Cellular networks are largely utilized in HetVNet to provide large coverage and high throughput to vehicular users. This brings new challenges as the heterogeneity of wireless infrastructures. With unified SDN network virtualization and abstraction, the integration of heterogeneous network technologies in vehicular networks became simple and transparent. Indeed, SDN promises to bring flexibility, scalability, and programmability for vehicular architectures, which can simplify the network management, reduce the cost and improve the performance of HetVNet. In this paper, we first highlight the limits of current HetVNet architectures and show how SDN paradigm can bring as a new solution to overcome these limitations with a focus on some use-cases. We also provide a taxonomy of existing softwaredefined vehicular architectures and discuss their limits. Based on this discussion, we continue by proposing a new SDN-based architecture for HetVNet. It is an agile cluster-based architecture adapted to both infrastructure-less and infrastructure-based scenarios. Finally, we demonstrate the feasibility and the efficiency of the proposed architecture compared to the related SDN-based HetVNet architectures via the simulation results.

II. SOFTWARE-DEFINED IN HETEROGENEOUS VEHICULAR NETWORK: OVERVIEW AND TAXONOMY

In this section, we briefly review the limits of existing HetVNets architectures, present benefits of integrating SDN paradigm in vehicular networks, describe some use cases and discuss a taxonomy of software-defined vehicular solutions.

Ahmed Alioua * , Sidi-Mohammed Senouci * * , Samira Moussaoui * , Hichem Sedjelmaci * * , and Abdelwahab Boualouache *

A. Current Heterogeneous Vehicular Architecture Limitations

Although the popularity of current HetVNet architectures [START_REF] Zheng | Heterogeneous Vehicular Networking: A Survey on Architecture, Challenges, and Solutions[END_REF], several limitations still exist. In addition to the heterogeneity of existing network infrastructures which causes challenges in network management and integration [START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF], we can cite for example, (i) the lack of scalability: it is very difficult to deploy services on a large scale, very dense and highly dynamic topology such as vehicular networks [START_REF] Ku | Towards software-defined VANET: Architecture and services[END_REF], (ii) the lack of intelligence: the heterogeneity of the vehicular equipment and their characteristics such as no programmability and the dependency to providers in development make these architectures rigid and difficult to manage, and (iii) the lack of flexibility and adaptability: given the diversity of deployment environments and the heterogeneity communication technologies, it is difficult to select the adequate technology to use according to the actual context and the fast changing of network parameters. These constraints limit the system functionality, slow down the creativity and often lead to the under-exploitation of network resources. Indeed, the solutions offered by these architectures are generally adapted only for a specific context or particular situation.

B. SDN Benefits for Heterogeneous Vehicular Networks

SDN has emerged as an attractive approach to improve the flexibility, programmability, efficiency and scalability of current network architectures. In addition, to the generic advantages that it brings to both wired and wireless networks, SDN keeps some unique benefits especially adapted to vehicular networks. Indeed, with the global awareness of network topology provided by the logically centralized control, it becomes easy to efficiently allocate all types of network resources (e.g., bandwidth, spectrum, power transmission, etc.). In one hand, the performance of existing vehicular architectures can be enhanced and better exploited by adapting the deployment of the most suitable solutions for each specific situation and adjusting the system parameters according to the actual context. In the other hand, with virtualization and abstraction that SDN brings, the integration of heterogeneous network technologies in vehicular networks becomes simple and transparent. In the following, we describe some use-cases that can be enhanced by software-defined HetVNets: SDN-based global dynamic map: in traditional vehicular networks, vehicles collaborate with each other and exchange different information collected by their sensors to build a local dynamic map ( L D M ) o n network conditions. This LDM contains static information such as road signs and dynamic information such as traffic and weather conditions. Integrating SDN into vehicular networks allows to the controller to centrally manage and maintain a global dynamic map (GDM) by collecting and filtering distributed vehicle LDMs. This allows the controller to get and construct a global dynamic view over the whole (or a part) of the network state, which can be used to make more informed and refined decisions as a reply to vehicle requests.

SDN-based offloading:

Offloading consists of the transfer of a task to an external entity when it cannot be performed locally due to the lack of necessary resources. In traditional vehicular networks, the offloading decision is made based on a limited knowledge of the networks. Indeed, this decision is based, for example, on historical network parameters [START_REF] Nirjon | Multinets: A system for real-time switching between multiple network interfaces on mobile devices[END_REF], which cannot reflect the current network state and even results in a non-beneficial decision. Besides, in the SDN-based vehicular networks, using the SDN controller centralized global view can dynamically make better profitable offloading decisions based on real-time networks state, which is more suitable to user's requirements and adapted to current network conditions.

C. Taxonomy Discussion on Software-defined Heterogeneous

Vehicular Networks software-defined heterogeneous vehicular networks (SDVN) architectures have recently been proposed. Table 1 gives a short overview of these architectures considering main characteristics such as the number of used controllers and the support from the infrastructure. Based on the number of used SDN controllers, we can classify these architectures into two categories: (i) Uni-controller architectures [START_REF] Ku | Towards software-defined VANET: Architecture and services[END_REF][START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF][START_REF] Liu | A Software Defined Network architecture for GeoBroadcast in VANETs[END_REF][START_REF] Huang | A Hierarchical Pseudonyms Management Approach for Software-Defined Vehicular Networks[END_REF][START_REF] Wang | Improved Rule Installation for Real-Time Query Service in Software-Defined Internet of Vehicles[END_REF]: These architectures use a unique controller that can be installed somewhere in the fixed infrastructure to handle all the network demands, and (ii) Multi-controllers architectures [START_REF] Zheng | Delay-Optimal Virtualized Radio Resource Scheduling in Software-Defined Vehicular Networks via Stochastic Learning[END_REF][START_REF] Truong | Software defined networking-based vehicular Adhoc Network with Fog Computing[END_REF][START_REF] Salahuddin | Software-Defined Networking for RSU Clouds in Support of the Internet of Vehicles[END_REF][START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF]: These architectures use multiple controllers installed over the fixed infrastructure, where each one handles a part of the network.

The use of a unique controller in such dynamic, large, and dense networks as vehicular networks is challenging for several reasons we can cite for example (i) a serious risk of controller bottleneck confronting to the huge number of requests, (ii) a high installation delay of flow rules is generated especially when the distance between vehicles and the controller surpasses hundreds of kilometers, and (iii) omnipresent risks of reliability and security are raised especially with such intermittent and unstable nature of wireless connections. Therefore, the use of multiple controllers is more appropriate with heterogeneous vehicular networks. Indeed, some architectures [START_REF] Wang | Improved Rule Installation for Real-Time Query Service in Software-Defined Internet of Vehicles[END_REF][START_REF] Zheng | Delay-Optimal Virtualized Radio Resource Scheduling in Software-Defined Vehicular Networks via Stochastic Learning[END_REF][START_REF] Truong | Software defined networking-based vehicular Adhoc Network with Fog Computing[END_REF][START_REF] Salahuddin | Software-Defined Networking for RSU Clouds in Support of the Internet of Vehicles[END_REF][START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF] of the second category propose to install controllers as nearest as possible to vehicles in order to obtain an acceptable end-to-end delay and better, some works in [START_REF] Ku | Towards software-defined VANET: Architecture and services[END_REF][START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF][START_REF] Truong | Software defined networking-based vehicular Adhoc Network with Fog Computing[END_REF][START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF] use fall back recovery system to ensure the availability of service if one of the controllers fails.

However, as we can notice in Table 1, all the available solutions are infrastructure-based architectures, i.e., they can only operate on the infrastructure-covered zones. This assumption seems strong one, especially with the first steps deployment of HetVNets, where the total coverage is far to be achieved. Motivating by this strong assumption, we tended to propose an architecture that can operate not only in infrastructure-covered zones but also in uncovered zones. Indeed, the proposed architecture, presented in the next section, is a semi-centralized SDN-based HetVNet architecture that supports heterogeneous communications: vehicle to vehicle (V2V), vehicle to infrastructure (V2I), infrastructure to infrastructure (I2I), and infrastructure to Cloud (I2Cloud).

III. PROPOSED ARCHITECTURE

In this section, we a novel flexible semi-centralized architecture for an SDN-based architecture for HetVNets, called cluster-based software defined heterogeneous vehicular networks (CSDHVN). It is based on a combination of different promising concepts that aim to: (i) extend traditional vehicular network resources capabilities by integrating already existing and largely deployed cellular networks (4G/5G) and high resources Cloud computing, (ii) partition and reorganize the network through clustering techniques to reduce interferences and overhead, and better support scalability, density and mobility, and (iii) use the emerging concept of SDN with hierarchically distributed multi-controllers to mitigate network heterogeneity and introduce flexibility, programmability, and facilitate the network management. The control in this architecture is semi-centralized: centralized in covered areas (i.e., infrastructure-based zones) where the coverage of the fixed infrastructure is available, and distributed multi-hops in uncovered areas (i.e., infrastructure-less zones) where the coverage of the fixed infrastructure is not available. The description of this architecture is detailed in below.

A. System Architecture

The basic idea of our architecture, as illustrated in Fig. 1, is summarized as follows: (i) based on the availability or not of fixed infrastructure coverage, we divide the network into two zones: covered infrastructure-based areas and uncovered infrastructure-less areas, (ii) partition and organize the network topology according to certain criteria (e.g., mobility, position, etc.) into two hierarchical clusters: static level-1 clusters, which are formed during the installation of cellular base stations. They have a size equals to the radio range of a base station (LTE\eNodeB) and dynamic level-0 clusters, which are periodically formed and updated using clustering algorithms such as in [START_REF] R E M Y | 4 V 2 X : L T E f o r a C e n t r a l i z e d V A N E T O r g a n i z a t i o n[END_REF] for covered areas and in [START_REF] Remy | LTE4V2X -Collection, dissemination and multi-hop forwarding[END_REF] for uncovered areas. Level-0 clusters have a maximal size equals to the IEEE 802.11p radio range and regroup vehicles which are close to each other and have similar characteristics (e.g., direction, velocity, position, etc.), (iii) deploy a local mobile distributed controller on each level-0 cluster-head, (iv) deploy a central distributed controller on each level-1 cluster-head (i.e., cellular base stations such as eNodeB), and (v) deploy a global controller on the Cloudlet server. The architecture installs the multi-controllers in the network edge, physically close to vehicles to ensure a short end-to-end response delay and support delay-sensitive (safety) services requirements

The main novelty of the proposed architecture is that it provides a complete and flexible architecture with hierarchical multi-controllers that perform in both covered areas, in which the control is centralized through three hierarchical distributed multi-controllers and uncovered areas, in which the topology is structured in clusters and the control is multi-hops distributed through the local mobile controllers at cluster-heads. In this case, local controllers collaborate and communicate with each other to construct a backhaul for system communications. The uncovered areas can also be used as a fallback recovery mechanism in covered scenarios when the connection with central controllers is lost. The proposed architecture is agile, when a vehicle leaves a covered zone to an uncovered zone and vice versa the system switches between an infrastructure-based centralized control and an infrastructure-less distributed control to ensure the continuity of service in a transparency way.

To allow SDN to operate on traditional HetVNet equipment, the architecture proposes to add an SDN module that offers necessary hardware (i.e., computing and storage unit) and software (i.e., SDN operating system, hypervisors and network services, etc.) resources to enable these equipment to support SDN, as illustrated in Fig. 1. To avoid adding new materials and limit the hardware modifications, the architecture prefers to reuse, if possible, the available computing and storage resources of the network equipment. The SDN architecture of our architecture is described in below.

B. SDN Architecture

Our architecture is based on the three SDN layers:

1. Data plane layer: It consists of all network equipment that only performs the collection and the forwarding of data information, i.e., mobile vehicles cluster members, roadside units (RSUs) and all network components between the base station and the cloudlet server. The data plane is divided according to the compounds' mobility into two types:

-Fixed data plane: It is known as fixed because it consists of static RSUs, which provides a support for V2V communications when two neighboring vehicles cannot communicate with each other, and all the fixed network forwarding equipment between the cellular base station and the cloudlet server.

-

Service and Applications layer:

It contains all the business applications installed on the controllers.

Communication interfaces:

Currently there are neither standardized SDN interfaces for directly integrating SDN into HetVNets, nor an ad-hoc (no IPoriented) version of OpenFlow protocol compatible with security applications features of HetVNet. Thus, we propose to use a customized version of OpenFlow protocol adapted to HetVNet scenarios as southbound API to communicate between the control plane and the data plane and to use a customized interface as Northbound API to communicate between the control plane and applications [START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF].

C. Fall Back Recovery Mechanism

Among fall back recovery mechanisms for SDN in HetVNet available in the literature, one initiative [START_REF] Ku | Towards software-defined VANET: Architecture and services[END_REF] proposes to switch to the traditional vehicular networks when the unique controller fails. This assumption may increase the complexity of software and hardware design [START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF]. Another initiative [START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF] uses a trajectory prediction to pre-install entries in the flow table, which can be used if the controller fails. But, this initiative does not envisage any solution if the failure lasts after the end of the entry lifetime. In [START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF], the authors use two types of hierarchical controllers, and if the high-level controller fails, the low-level controllers collaborate together to ensure the service. This solution only considers the high-level controller failure and does not support low-level controller failures.

Our architecture is based on the use of a hierarchy of distributed multi-controllers. As a fallback recovery mechanism, we propose to permanently anticipate the possible failure of each controller at all levels and prepare the recovery scenario in advance while exploiting intelligently and efficiency the hierarchy of controllers. Therefore, a list of candidate recovery controllers is permanently managed by each local controller. The identifier (id) of the best candidate is periodically communicated to all level-0 cluster members and stored in a newly added recovery field in the flow table. Therefore, if an upper controller fails (level-2, resp. level-1), the architecture will switch to a multi-hops distributed control scheme in which the controllers of the strictly lower level (level-1, resp. level-0) takes over the service and collaborate with each other to ensure service continuity. If a low-level controller (level-0) fails, the pre-prepared recovery controller will take over to ensure the service continuity. Vehicles can directly start their requests to this recovery controller who is the corresponding identifier is pre-installed in their flow tables.

IV. SIMULATION RESULTS

In this section, we present our simulation configuration and results. The simulation scenario is implemented using the network simulator NS3 [START_REF][END_REF] and the traffic mobility simulator SUMO [START_REF]Simulation of urban mobility (sumo)[END_REF]. The main purpose of these simulations is to demonstrate the reliability and the efficiency of the proposed architecture and study the impact of the controller deployment distance on the average flow rule installation time. For simulation, we consider a simple HetVNet scenario similar to that illustrated in Fig. 1, where the network topology is deployed in 10000 x 10000 m area. The eNodeB is situated 1000 m far from the road. The node density is 100 vehicles. Each vehicle has a velocity between 15 and 25 m/s and it is equipped with a 4G cellular interface and an IEEE 802.11p interface.

In the evaluation illustrated in Fig. 2, we simulate a scenario where a vehicle moves passing by an uncovered road segment where the connecting link with the central controller is not reachable even because of obstacles (e.g., high building, tunnel, etc.) or because of the absence of the fixed infrastructure. Afterward, we evaluate how our architecture (CSDHVN) with the multi-level hierarchical controllers reacts to this situation. We compare the performance of the proposed architecture with others SDVN infrastructure-based works in [START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF][START_REF] Nirjon | Multinets: A system for real-time switching between multiple network interfaces on mobile devices[END_REF][START_REF] Liu | A Software Defined Network architecture for GeoBroadcast in VANETs[END_REF][START_REF] Huang | A Hierarchical Pseudonyms Management Approach for Software-Defined Vehicular Networks[END_REF][START_REF] Wang | Improved Rule Installation for Real-Time Query Service in Software-Defined Internet of Vehicles[END_REF][START_REF] Zheng | Delay-Optimal Virtualized Radio Resource Scheduling in Software-Defined Vehicular Networks via Stochastic Learning[END_REF], [START_REF] Salahuddin | Software-Defined Networking for RSU Clouds in Support of the Internet of Vehicles[END_REF], [START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF] (we called, SDVN Infrastructure-based works), that deploy the controller on the fixed vehicular infrastructure according to the packet delivery ratio, which represents the ratio of packets successfully received to the total sent. Fig. 2 shows that just when the vehicle enters into the uncovered infrastructure-less zone, the packet delivery ratio in SDVN infrastructure-based works starts to decrease dramatically and it still drops until the vehicle leaves the uncovered zone and the connection with the controller is established once again, after that, the system resumes a good delivery ratio. Contrarily, our CSDHVN maintains a good packet delivery ratio. This behavior can be justified by the fact that in the related infrastructure-based SDVN solutions in [START_REF] He | SDVN: enabling rapid network innovation for heterogeneous vehicular communication[END_REF][START_REF] Nirjon | Multinets: A system for real-time switching between multiple network interfaces on mobile devices[END_REF][START_REF] Liu | A Software Defined Network architecture for GeoBroadcast in VANETs[END_REF][START_REF] Huang | A Hierarchical Pseudonyms Management Approach for Software-Defined Vehicular Networks[END_REF][START_REF] Wang | Improved Rule Installation for Real-Time Query Service in Software-Defined Internet of Vehicles[END_REF][START_REF] Zheng | Delay-Optimal Virtualized Radio Resource Scheduling in Software-Defined Vehicular Networks via Stochastic Learning[END_REF], [START_REF] Salahuddin | Software-Defined Networking for RSU Clouds in Support of the Internet of Vehicles[END_REF], [START_REF] Kazmi | DeVANET: Decentralized Software-Defined VANET Architecture[END_REF], the SDN controller is installed somewhere on the fixed vehicular infrastructure and if the connection with this controller is lost or it is unavailable, the service will be interrupted due to the centralized control logic of SDN. More efficient, our CSDHVN architecture ensures a good packet delivery ratio even in the covered infrastructure-based zone or in the uncovered infrastructure-less zone, thanks to the multilevel hierarchical controllers and specially the local controller on the cluster head vehicle that takes over to ensure the service continuity when the connection with the controller on the fixed infrastructure is lost. This evaluation demonstrates the reliability and the efficiency of our CSDHVN architecture and confirms that the consideration of infrastructure-less zone in the design of SDVN architecture is primordial given the negative effect that represents on the packet delivery ratio.

We study in the evaluation illustrated in Fig. 3, the impact of the physical distance of controller deployment from the vehicles, on the flow rule installation time, which represents the elapsed time since a vehicle requests the controller for a flow rule and the time when it is installed in the flow table. Thus, we focus on a scenario of a set of vehicles connected to a controller and we varied the distance between the vehicles and the controller for different vehicles number. Fig. 3 shows that the average flow rule installation time increases with the increase of vehicles number and the controller deployment distance. Also from Fig. 3. we can conclude that to ensure a flow rules installation time sufficient to satisfy the lower latency requirement of the most of vehicular road safety applications (≤ 100 ms [START_REF] Zheng | Heterogeneous Vehicular Networking: A Survey on Architecture, Challenges, and Solutions[END_REF]) in such dense networks as HetVNet, the SDN controller must be installed on the edge of network, the nearest as possible from the vehicles (no far than 5 km). Our CSDHVN architecture is based on multi-level hierarchical controllers. The low-level controller (local controller) is installed on the cluster head vehicle, no more than 300 m far of vehicles and the second, central controller, on the eNodeB (far about 1 km). This can ensure a low flow rules installation time and better handles the delaysensitive and low latency road safety applications.

V. CONCLUSION

Based on the taxonomy discussion of SDN-based HetVNet architectures, we conclude that the current general tendency should be the use of multiple distributed controllers installed on the edge of the network with an efficient fall back recovery mechanism. Moreover, the uncovered infrastructure-less zones should be considered in the design of SDN-based HetVNet architectures. Consequently, we present in this paper a semicentralized flexible SDN-based HetVNet architecture with hierarchical multi-controllers installed on the edge of the network. Our SDN-based architecture is robust thanks to an effective fallback recovery mechanism, and works in both covered and uncovered areas. We also demonstrate the feasibility and the efficiency of our proposed architecture compared to the related SDVN infrastructure-based works based on simulation results.

The implementation complexity and cost, the high mobility of vehicles, and the dense network topology, rest open challenges in front of SDN integration in VANETs. As future work, we plan to perform more intensive experimentations to proof the efficiency of the proposed architecture.

Fig. 1 .

 1 Fig. 1. Cluster-based software-defined for a heterogeneous vehicular network.

Fig. 2 .

 2 Fig. 2. Effect of uncovered zones on packet delivery ratio.

Fig. 3 .

 3 Fig. 3. Effect of Controller deployment distance on flow rule installation time.


Playing hide and seek : Is there a Jewish way to it ?

Frank Alvarez-Pereyre

The task of depicting Jewish thought is a tricky one. One is supposed to account for the very way Jewish thought models itself, makes itself be what it is. This implies that we should be able to report about the internal categories and about the internal processing that together lead to what Jewish thought appears to be.

By the moment one tries to face such a challenge, two methodological options might be chosen, each of them being linked to distinct theoretical perspectives.

According to one of these options, we should look for the very way Jewish thought expresses itself on the subject. We should collect every explicit theorization that Jewish thought would produce about itself, and then organize an inventory of these internal statements. Such a option has got an obvious bias yet. Collect and organize being on the side of the scholar, trying to account about Jewish thought in its very own words seems quite difficult. If going along the second option, the scholar would refrain from conveining any internal self-definition. He would depict its object on the basis of its usual set of tools, taking a totally external stand towards its object of investigation. He would report about what he can observe, measure and analyse as an historian, or as an anthropologist, a musicologist, a linguist or a philosopher. But then, how would this scholar be certain that his work is fully relevant ? Would his findings match the internal categories that are recognized by the Jewish thought itself ? More than that : who is to account for the internal categories ? How do we get to it ? Each of these options has got further limitations. As for the first one, by the moment it focuses about self-definitions, it firstly presupposes that such selfdefinitions are totally satisfactory, and that they account for any phenomenon, content, structure, and strategy. It presupposes also that everything can be properly labelled through language, when the very elaboration and developpement of Jewish thought encompasses many dimensions, the nature of which does differ from the very linguistic way of processing. As for the second option, its limits begin when one realizes that the independant work of the musicologist, philosopher or linguist cannot face the very complexity of the objects. These objects are to some extent an object for the linguists. To some extent, and not in the same way, these objects are an object for the anthropologists, the historians, the sociologists or the philosophers. Each of these scholars will have a restricted look at the material, inside the limits of the analytical considerations that are recognised by each discipline when dealing with the objects that are said to be the relevant ones for any of them.

In the following pages, we shall try to report about the ways Jewish thought does what it does taking the following theoretical stand. We shall consider that the two above mentionned options should be considered equally and articulated. Parallely, the above listed limitations should not hamper our investigation. They should lead to specific considerations in terms of methodology. Thus, we firstly propose that the external approach to the objects for investigation should combine -and not separatethe available academic fields in order to account for the very complexity of the selected objects, be it in terms of structure or in terms of dynamics. We propose an interdisciplinary approach to the facts under study. The two domains that have been be selected for our survey -namely Jewish liturgy and the Jewish languages -logically call for a combined movement where linguistics, anthropology, ethnomusicology, and history have their say. Secondly, we propose that one should surely aim at eliciting the internal categories knowing that, fundamentally, such internal categories express themselves in different and complementary ways, and not solely through explicit linguistic statements. More than that : if they express themselves, it is often through a constant process of hide and seek. And if such a process proves to be a necessary one, we have to take such a factor into account when considering the methodology to be used. To sum it up, we suppose that an interdisciplinary approach to ritualised performances and to language behaviors might lead us to reach and elicit internal categories that would find parallel and complementary expressions through other channels : be it in the biblical, the midrashic or the legal corpuses, be it in the paraliturgical repertoires, or any cultural object or social behavior where Jewish thought might be at work.

A last important point should be clarified in these preleminary statements. We suppose that the expression « Jewish thought » refers to a complex set of principles and developements, of concepts, contents and processes that have been shaping the life of the Jewish people throughout the centuries, whatever the domains of activity one focuses upon, whatever the types of persons, whatever the institutions. If so, we should then examine different settings and practical activities, so as to account for the possible, and perhaps necessary, complementarity between the concepts, the contents and the processes at work. In other words, one should turn to distinct practical social and cultural settings or activities in order to report about possible specific concepts, contents and processes that would have an equal importance, and a genuine raison d'être. The preceding arguments explain that the present paper will focuse on two types of activities pertaining to Jewish life. It remains to be seen to what extent such diverse concepts, contents and processes are themselves bound together at a higher hierarchical level of understanding. It remains also to be seen which status should be attributed to visible evolutions throughout history. In other words, what are the nature and the implications of such evolutions through time ? Does an evolution really change something to any model or principle that would have been valid so far ? Does it ultimately reveal something about the models and the principles, and about the way Jewish thought deals with time, change, and variation ?

Jewish liturgy

When speaking of Jewish liturgy, we are facing differing series of situations, and very varying types of material. Do we mind the liturgical calendar, or the evolution of the prayers, their text and music, throughout the ages ? Do we focuse about the protagonists of the litugical occasions, about one or another of the regional variants, about the differencies between liturgical and paraliturgical repertoires ? Whatever the element we would choose, we would have to ask the following question : beyond the common identification of the repertoires, protagonists, circumstances and materials, how are the different elements modelled and organized inside the Jewish world ? Is there a Jewish way to it ? A question that would be echoed by such parallel question as « Does each of the monotheistic faith handle things differently and to what extent ? ».

Actually, we shall focuse on one phenomenon, namely the ritual cantilation of the biblical text. This is a central moment inside the liturgical activity itself. It is shared throughout the Jewish world, and it has been a compulsory phenomenon throughout the ages. At some point, we shall also turn to the cantilation of portions of the talmudic text : an aspect that has been rarely documented, but that greatly helps us understand the ways Jewish thought depicts itself [START_REF] Adler | The Study of Jewish Music[END_REF][START_REF] Idelsohn | Jewish Music. Its historical development[END_REF].

Taking an ethnographic look at the biblical cantilation, one comes to an inventory of what could be labeled its compulsory constitutive elements. We have got aboundant sets of texts, an important musical material, gestures at some point, together with a serie of conditions that determine their ritual definition and linking, but also the number of the participants, their quality and their relationships, and finally the temporal and spatial organisation of liturgy. To sum it up, we are confronted to the following question : what is at stake behind what appears to be a highly sophisticated process where very different types of constitutive elements come together ? At some point of the usual Shabbat service in the synagogue as well as on holydays, and also on Mondays and Thursdays yet with a shorter portion of text to be read, a Torah scroll is taken out of the Holy Arch inside of the synagogue. The scroll having been opened, a man comes to read out of it, with someone on his left handside, and someone on his right handside. On the right hand side will stand in succession seven men or youngsters aged at least 13 on Shabbath -and five instead of seven on holydays -, to begin with a Cohen and then a Levy (or any other person in the case there is no Cohen and Levy). After the reading of the weekly portion of the Torah (namely out of the five books of Moses), a portion taken out the prophetic texts will be read by an additional person, on Shabbath and on holydays. This prophetic portion is, in the very big majority of the cases, not read out of a scroll.

What happens now when considering the one who reads, and the one who is standing on his left handside ? The one who reads out of the scroll reads and sings alltogether. The one on his left handside does follow on a copy of the biblical text, and may perform different hand gestures parallel to the reading and singing of the biblical text. It may happen that this very person, or another person who is attending the service, corrects the one who reads and chants out of the scroll. What is now to be understood under the terms text, music and gesture ? And what is to be understood when considering the relationship between the protagonists ? Let us have a look at the scroll by the moment the reader in charge is acting. There is no musical score on it, but the musical performance that is produced by the one who reads is systematic and quite elaborated. As for the text, one realizes that only its conconantic aspect is to be found on the scroll. No visible vocalization is available on the parchment. No ponctuation either. The individual words of the texts are separated from each other, but you cannot see where a verse begins and when it ends. Yet, the one who reads and chants systematically produces a full text, in terms of vocalization, internal ponctuation of the verses, discursive organization of the verses as they come one after the other. On the scroll, the biblical text remains a very minimal one.

We shall now turn to what the man on the left handside reads. It is a « normal text », in a « normal book ». This meaning that a good proportion of what appears to be lacking on the scroll is now available. Each word appears with the consonants and their vocalization. The verses are visibely isolated from each other in a visible way.

And every word has got graphic signs under or above, and these are supposed to represent the musical side of the chanting, or to guide it. But what is the relationship betwenn a graphic sign and a musical motive ? The more so that the gestures that the man on the left might perform appear to be the equivalent -a physical, a spatial and a visual representation -of the graphic signs, and of their musical rendering.

At that point we have to admit that the one who is facing the scroll is performing a complex action, the elements of which are largely absent when considering the practical basis for it, namely the scroll. On the other hand, the man on the left hand side alltogether makes sure that the reader does not do any error in the reading and the chanting, namely that the reader is well aware of the vocalisation of the words, of the ponctuation of the verses, and of the musical rendering of the text. Fundamentally, the one who « reads » out of the scroll adds what appears to be an oral knowledge of the text to what lies in front of his eyes.

When going to a specific inquiry of the musical material that is orally conveyed by the one who reads out of the scroll, we learn that the musical motives and their succession help indicate the word accent for the words of the texts. They also help establish the separation of the successive verses, and the internal organisation of each verse. Ultimately, the musical motives function as a syntactic device for the verses.

They add a supplementary organization for the syntax of the text to what would be considered the most basic formal organisation of the verses from a mere syntactic point of view. Such a supplementary organization has got an importance in itself. For it is totally linked to the interpretation or hermeneutics of the biblical text.

To sum up at that point, we shall say that there is no fully acurate and complete materialization of any of the basic constitutive elements of liturgy. On the contrary, there seems to be a constant shift, a constant drift. The text that appears on the scroll is lacunary. The music materializes vital aspects of the text. The gestures signal something of both the textual and the musical dimensions. And all this goes along a strictly ritualized performance, with a tight interplay between an oral and a written side.

The ones who are familiar with the history of the biblical and non biblical texts, and with the massora, will have understood that the ethnography of the liturgy is but another image of a well known phenomenon. And the ones who are conversant with some aspects of the Jewish thought surely felt also at home. What is the point here ?

And what is the use of ethnography if answers are already available elsewhere, if existing concepts and internal categorisations are already self-speaking ? History tells us that two graphic systems -for the accentuation and ponctuation of the verses -have been materialized in the first centuries of the Christian era, in conformity with a thourough elicitation of the linguistic organisation of the verses inside the biblical text. Yet, the graphic systems would not find their way into the scroll.

It had to remain outside of it. These graphic systems corresponded to a linguistic analysis as such, but it could not physically enter into the scroll. The same with the musical motives. These ones already existed but no musical representation of the chant would enter the scroll. What has been called the Written Law, inside of the Jewish thought, had and has to remain fundamentally linked to an oral set of elements and phenomena that garantee the full identity of the text to be conveyed. Some parallel developpement happened on the side of the Oral Law. The hudge collection of the interpretative texts -including their legal processing -has been foundamentally an exclusive oral corpus. And then the Talmud and lots of midrashim were written down during the first centuries of the Christain era. But such a switch had to comply to one basic condition : the written text of the oral law should appear solely under its consonantic aspect. No vowel should appear on the paper. More than that, no visual cue to the different aspects of ponctuation should be available. This meaning that any « reader » of the oral law had, and still has to know how to organize the flow of the written text when considering its ponctuation, when considering the basic sentences, but also the minute discursive organisation of these sentences. To that end, complex systems have been established inside the Jewish communities, systems that again belong to the domain of oral transmission. Such systems could be named the hidden teamim for the reading and the studying of the Mishna and the Gemara.

They are extremely sophisticated but they have to remain invisible at the surface of the written and lacunary « text ». As a matter of fact, many insiders are largely unaware of the hidden structural rules that govern the cantilation of the Oral Law, and the scholars did not really pay attention to them neither [START_REF] Alvarez-Pereyre | La transmission orale de la Mishna[END_REF][START_REF] Alvarez-Pereyre | The rules of the Oral transmission of the Mishnah According to the Aleppo Tradition[END_REF].

Let us now reflect briefly about the situation when considering the classical understanding of such notions as « text » and « music », or the written and oral evidences. On the basis of what ethnography tells us, the written text is lacunary and its only through its oral rendition that it comes to its full existence. The formal and semantic aspects of the text come to an existence under the condition that music and intonation -and even hand gestures -are fully involved in the context of the oral rendering. Such fundamental principles are equally governing the transmission and study of both the Written and the Oral Law. But in such a way that the respective identity of both of them is kept, in order to maintain their necessary articulation. At that point, we can come back to the question of the use of any ethnographic approach.

We could say that the ethnographic approach matches what we know about the principles that the tradition of the Sages stresses in its own words : that a sharp distinction, and a vital complementarity, should be kept between the Written and the Oral law. We can add that such principles do not remain principles in the context of liturgy, and in the context of the study of Talmud. They are turned to a highly ritual performance, that makes such principles literally live through the effective rendering of the texts in all their aspects. This ritual performance not only makes the principles At that point, and interistingly enough, it might be worthwhile to briefly turn to a comparison of the three monotheistic faiths on the same issues. The problematics of the relationship between a written and an oral side is shared. It is shared on the basis of a minute set of material evidences and also on the basis of strict ritual rules that echo what we have already encountered on the side of Jewish liturgy. Yet, there are clear differences on these very points. What type of an issue do such convergences and differences manifest ?

On the side of Christianity, the available languages (latin, greek, romanian, french, and so forth) do not enable to play with the two consonantic and vocalic sides of a language, contrarily to what happens with Hebrew and Arabic. The potential separation of the two sides in the case of these two languages is a key resource in the case for Judaism and Islam when coming to the practical « acting » of the differences and relationships between orality and its written counterpart. It is not the case for Christianity.

When considering the discursive organisation of the texts, Greek orthodoxy has developped three different graphic systems that each function for a specific need and that are made visible on the written text : internal punctuation of the verses, discursive ponctuation of the successive verses, indication of the nature and status of the different liturgical texts inside the tradition [START_REF] Flender | Der biblische Sprechgesang und seine mündliche Ueberlieferung in Synagogue und grieschicher Kirche[END_REF].

Islam did not indicate the vocalization of the words on the written text of the Coran for a period of time, nor the boundaries between the successive verses. Then it introduced a graphic indication for some of the short vowels and it introduced the graphic indication of the verses' ending : all these elements appearing on the text of the Coran as it is read during the liturgical event. As for music now, it is not only impossible to find any trace of it on the text of the Coran but, on the principle, no written representation what so ever should be given of the cantilation as it is performed orally by the one who reads and chants. Still, the oral rendering of the « written » text remains the medium through which the minute syntactic organisation of the latter is made effective (Ben Otmane 1995).

The very linguistic parameters which serve as the base for the oral rendering of the Coran parallel in nature the linguistics parameters that serve as a base for the study of the Michna and the Talmud. More generally, such linguistic parameters are to be found valid for the oral rendering of the Biblical text. Yet, a sharp distinction should be made if speaking of the functions of the parameters. The Talmudic corpus is bound to argumentation and interpretation, and to the legal implications of it. The Biblical « text » and the Coran do serve a quite different purpose. They convey the sacred word, or the words of the Prophet. They are properly the materialization, through the human expression, of the divine expression.

Here really lies the crucial point, philosophically, legally and cuturally speaking.

The divine verb has to be made audible as such. Such a necessity, yet, implies what we have called the principle of a constant shift or drift through which it is made clear that the human expression is by no means the equivalent of the divine one, and that the divine expression cannot find its proper vehicule through the human expression.

Liturgy makes God's presence effective, it is a living enacting of God's expression. The rites that are attached to liturgy underline how far such an enacting is binding. No less binding, yet, is the legal and the philosophical impossibility for humans to fully represent God's expression. More than that : the ritual has to show that there is a profound separation and distinction between God's expression and man's expression.

When coming to a comparison between the three monotheistic faiths on the basis of their liturgy and to their practical differences, one would propose that such differences relate to their varying understanding of what is called the Divine Presence and Verb, and also to their internal and respective understanding of the concept of idolatry.

Jewish languages

In the course of time, starting already before the tenth century of the current era or around it, the Jewish communities of the Diaspora have developped languages that have been specific to them and that were not shared by their non Jewish neighbours.

Parallely, the Jewish people inside these communities systematically got aquainted with the languages of their neighbours, whatever the places they lived. Linguistic intercourse with the non Jewish neighbours has been a necessity, and it was also vital for the Jews to have a language of their own, for their own purposes. But what type of a language ?

The scientific interest for the languages that were used inside the Jewish communities arose around the middle of the XIXth century. At that time, the specialists of the German or the Spanish languages did find in the written testimonies of the Jewish communities a very usefull documentation they could not find elsewhere, as they were studying the history of Spanish or German, for example. For the historical shaping of the linguistic and social standards for these languages had meant a sharp diminution of their regional or local peculiarities, their long standing social disqualification and the absence of a systematic scholarly interest into it. For reasons that were internal to the Jewish communities and that relate to the obligation of keeping track of the encounter with the non Jewish world through time and space, the active memory of what makes the identity of the non Jewish world had led to the preservation of many linguistic testimonies for the co-territorial languages the Jews would find wathever the place they lived. Parallely, still during the finishing XIXth century and the beginnings of the XXth century, lay persons or scholars would aim at collecting the Hebrew elements that were to be found inside a given Jewish language according to its regional variants, or that would appear inside the national coterritorial languages or local dialects the Jewish people would encounter and master.

From 1970 onwards -starting with the pioneering work devoted by Max [START_REF] Weinreich | Geshikhte fun der yidisher shprakh[END_REF] to the Yiddish language -the different Jewish languages have come to be a fullfledged scientific object [START_REF] Paper | Jewish Languages. Theme and Variations[END_REF][START_REF] Pe'amim | [END_REF][START_REF] Gold | Jewish Intralinguistics as a Field of Study[END_REF][START_REF] Wexler | Jewish Interlinguistics : facts and conceptual framework[END_REF][START_REF] Benabu | Judeo-Romance Languages[END_REF]. It was then supposed that they shared a lot and the question arose quite quickly of their common characteristics. Three essential features were listed as such at this initial phase.

First of all, these languages were thought to be exclusively Jewish when considering their usage : they would serve the specific needs of the community, be it the day to day conversation, be it the translation of the biblical text or of the prohetic portions called haftarah (for those who would not master the Hebrew language sufficiently), be it for commercial or legal purposes. Besides of this sociolinguistic feature, two features were clearly identified on the linguistic side.

The Jewish languages were created by mixing together language elements that would come from varying existing foreign and co-territorial languages. They all would have a Hebrew and Aramaic component, and then also Spanish in the case of Judeo-Spanish, but also some Greek, or some Turkish, or some Arabic and French, according to the very place the Judeo-Spanish speaking Jews have lived throughout the centuries.

In the case of Yiddish, we have Hebrew and Aramaic, together with German, but also Polish, Ukranian, or Russian, whenever the case and according to the regions where the Jews have been living in the course of time. As for Judeo-Arabic, we have Hebrew, Aramaic and Arabic, but the nature of the Arabic material might differ according to the very dialects that were spoken in the different places where Jews have been living throughout the centuries in a close relationship to Muslim people. The second linguistic feature that has been shared lies in the writing system. All of the Jewish languages have been written down with the Hebrew alphabet. As a matter of fact, the two mentioned linguistic features turn to have decisive implications on the sociolinguistic side. The above listed traits lead to a highly singular medium for communication that is shared only inside of the Jewish community, with no possibility for the foreigners to have access to it (Histoire, Epistémologie, Langage 1996 ;[START_REF] Alvarez-Pereyre | Linguistique des langues juives et linguistique générale[END_REF].

What is now the rationale behind all this ? Does such a phenomenon have any relevance from the point of view of Jewish thought, and more precisely when considering its practical elaboration ? At that stage, we can say that the Jewish languages have been elaborated on the basis of a strong common objective : to ensure that the Jews would maintain their own identity, throughout the generations and whatever the place they lived. Interestingly enough, it is when we turn to general linguistics and to linguistic typology that we learn more about the Jewish languages, about their structuration and even about their anthopological signification.

Reading Max Weinreich's seminal work on the Yiddish language, we learn that the Jewish languages would be the result of a threefold operating principle : selection, fusion and convergence.

The term selection refers to the fact that the linguistic material that would be thought potentially relevant inside the non Jewish languages is taken from these languages in order to enter the Jewish languages. This implying that not everything is coming into the Jewish languages.

The term fusion indicates that any material coming from whatever non Jewish language is mixed together to make a fullfledged Jewish language of its own, together with a substantial Hebrew and Aramaic component.

The term convergence indicates that selection and fusion go along converging patterns and follow similar processes, according to a principle of coherence that has something to do with the internal needs of the different Jewish communities, whatever the place and time they do live. Max Weinreich's History of the Yiddish language does refer to the many Jewish languages that developped over the centuries. It is when dealing with Yiddish specifically that Weinreich endlessly reports about the highly sophisticated and manifold way through which the above mentionned threefold principle works and operates. It appears that such a principle has been the leading, the shared -and the totally implicit -force that lead to the rise and development of the so-called Jewish languages.

Weinreich's work insists on another major factor that is common to all Jewish languages : namely the central presence of the Hebrew (and Aramaic) component. Such a presence is statistically impressive. More than that, the Hebrew component divides itself between the Hebrew evidences that are inserted as such inside the Jewish languages and the Hebrew linguistic elements that undergo phonological, morphological, lexical, syntactic or stylistic modifications [START_REF] Morag | The Hebrew Terms in the Jewish Languages : some general considerations[END_REF][START_REF] Asher | Paramètres pour l'étude des judéo-langues et de leurs littératures[END_REF].

The linguists who dealt with the Jewish languages in the three last decades of the XXth century generously contributed to the investigation of the Hebrew component whatever the Jewish languages under consideration. They confirmed the two paths through which Hebrew made its way inside the Jewish languages. They hinted to the hierarchical importance of the Hebrew and Aramaic component from the point of view of the linguistic structuring of the Jewish languages. They made it clear that Hebrew and Aramaic would serve linguistic and non linguistic purposes, with a double track developpment in each and the same Jewish language : keeping in line with the most essential messages of the cultural and religious tradition ; developping itself through a large variety of local peculiarities (be it on the phonological, the morphological or the semantic plane), and through a large scale linking to the other linguistic components.

Towards the end of the XXth century and by the beginning of the XXIst century the following points became clear to the linguists. First of all, the structural organization of the different Jewish languages was shared to a very high degree. This point is fundamental when we know that, when considering each of the Jewish languages, the non Jewish languages that have been a partial source for them do belong to differing linguistic families. In other words, languages that have been structurally different between themselves, and different structurally from the Hebrew and the Aramaic language (with the exception of Arabic) have come together into one and the same language, or into parallel languages, that have been sharing their most profound characters between themselves. All possible Jewish languages developped parallely, being bound to similar purposes and building themselves on the basis of strongly shared internal and implicit patterns.

Secondly, it appeared that there has been a hidden model that governed the threefold operating principle revealed by M. Weinreich. It was understood that the guiding model for the structural building of the Jewish languages has been the Hebrew language. Not only the Hebrew language as such and what it bears in cultural and philosophical terms, but also the Hebrew language as is has been systematically structured inside the biblical text and, equally, as it has been transmitted through the literal translations -a word by word translation i. e. « Humesh-Taytsch » or « Ladino » -into Spanish, German, Arabic or Persian. The translation process as a whole would have been a practical and leading filter when considering the very making of the Jewish languages [START_REF] Varol | Yiddish et judéo-espagnol : dynamique comparée de deux langues de Diaspora[END_REF].

Thirdly, it was made clear that all the Jewish languages were persuing a double and parallel objective [START_REF] Bornes-Varol | Le judéo-espagnol d'Istanbul[END_REF]. For there has been a constant balance between the linguistic characters that were directly depending on the Hebrew and Aramaic languages, and the ones that were depending on the non Jewish source languages. This explaining the very strong similarity between the Jewish languages, as well as the reality of variation, inside a given language, and between these languages. But what for ? On the one hand, it would be possible for the people of the Jewish communities to deal with their own needs and interests, and to be constantly emerged into the hebraic heritage through the medium of language. On the other hand, the Jewish languages would serve, inside of the communities, as a medium that would enable the minute analysis of the foreign societies and cultures and the day to day aquaintance with these societies and cultures. This meaning that a double awareness was made possible through one and the same Jewish language : an awareness, a sense of belonging, enabling more generally a capacity to be a full insider on the side of the Jewish heritage ; and also a clear knowledge of and the practical capacity for differenciation when considering the non Jewish society and culture.

At that point, we should understand that behind such a complex and yet essential picture, two strong features are operating, that have been recognized as crucial for the definition of Jewish culture in action through history : translation and interpretation on the one hand, memorization on the other hand. These features date back to the historical and philosophical emergence of the Jewish People, and they did fully operate throughout history, before and after the Exile.

In their own terms, the Jewish languages enact these features for the sake of the Jewish communities that are facing two top and intertwined priorities at any time : perpetuating the Jewish identity, and coping with the outter world and patterns. It has to do so with a due consideration for the varied sectors, layers and components of the communities themselves ; with a due consideration for each of any other local environment ; and with the characteristics of any given period of time. Keeping due memory of the linguistic non Jewish environment explains itself in this context, together with the ongoing threefold process of selection, fusion and convergence where Jewish thought -massively through Hebrew and Aramaic -may ensure its perpetuation. It does so by means of a systematic and continued confrontation between the Jewish world and the non Jewish world (Alvarez-Pereyre 2018).

Let us take a step further and compare the Jewish languages to those institutions that have been so vital for the effective perpetuation of the Jewish communities and the Jewish heritage throughout time and space. The synagogue and the beit midrash on the one hand, the system of rules that defines casherout and the rules governing purity inside the family on the other hand have been recognized has having enabled such an active identity and its continuation up to now.

Besides of these elements and factors, the Jewish languages have been a highly unified medium that made it possible for the Jewish people to build themselves as individuals and as a collective body : ensuring that their chore values and needs be constantly elicited and transmitted and that their vital but complex relationship to their non Jewish counterpart be constantly elicited. These languages have been a tremendous and especially powerfull two track pedagogical tool. They served as a day to day medium that has been shared by all layers of the community, without blurring the internal differenciations between the layers.

Concluding remarks

Jewish liturgy and the Jewish languages have been very long standing realities.

Through them, very essential issues have been processed, each time in a highly intricate way that itself speaks for the importance of the two objets we have been considering.

One might have noted the quite overt character of the liturgy, and the strong covert character of the languages. The overt character of the liturgy is to be found in the very material we can observe directly in the context of continued liturgical performances. Yet, the meaning of it is not at all delivered as such. The covert character of the Jewish languages is a condition for something that cannot be deciphered easily.

More than that, with these languages, we are dealing with casual languages and day to day communication channels. And these appear finally to operate in a close relationship to vital issues for the Jewish people.

In both cases, we have been going through a systematic external consideration for the facts at hand. In so doing, and in the same time, we have been processing the evidences going well beyond the most classical approach when considering the different disciplines that were logically involved. Parallely, we have been asking ourselves about the anthropological implications of our interdisciplinary analysis. It is at that point that we could match the results of the scientific approach with what could be called the internal cultural categorizations. These do not come to you as such, and there is no short cut to it. It is when you inscribe yourself into the very world you are discribing that you might one day get a sense of it, a partial, a quite partial sense of such categorizations. Obviously there are different types of immersion. The one we refer to means acting inside, acting and observing, with a double intention : access to the internal categories as they are elicited in their most natural manner, and look for the internal categories on the basis of an anthropological perspective when such internal categories do not tell about themselves in a direct way.

In its own terms, liturgy is one phenomenon inside of a large serie of instances that elaborate -each in its own way -on the topic of the veiling and unveiling of God, its presence and manifestations : be it concepts, be it interpretations, be it other types of ritual phenomenon. In this context, we have proposed that liturgy aims at manifesting the Divine presence yet without having it represented as such. More precisely, liturgy is built in such a way that, on the human plane, the Divine Verb is transmited together with the principle and formal impossibility of representing it.

  be a living reality. It also embodies what has been called earlier the principle of a constant shift and drift. The ones who perform cantilation « perform » the principles, and also what these principles are supposed to convey more essentially (Alvarez-Pereyre 2006).

The languages of the Jewish communities appear to function in a close relationship to the topics of identity and belonging -in the broadest understanding of the terms -, their making on the daily basis, their preservation and teaching, in the casual conduct of life with its different registers. The Jewish languages are bound to assist the individuals and the collective body -with all its layers -preserve endogamy and cope with the outer world : both sides being a condition for the other one.

Two very different domains have been chosen for the present investigation. Each of them illustrates highly original processes. They together account for the high degree of plasticity through which Jewish thought makes itself effective. They even enable us to identify in a subtle way how Jewish thought establishes its own agendas and makes them actual throughout time and space.


Mathieu Roche
email: mathieu.roche@cirad.fr

Agneta Lindsten
email: agneta.lindsten@slu.se

Tomas Lundén
email: tomas.lunden@slu.se

Thierry Helmer
email: thierry.helmer@cirad.fr

LEAP4FNSSA lexicon: Towards a new dataset of keywords dealing with food security

Food security Semantic resources Agrovoc Text Mining a b s t r a c t

The main objective of the project LEAP4FNSSA (Long-term EU-AU Research and Innovation Partnership for Food and Nutrition Security and Sustainable Agriculture) is to provide a tool for European and African institutions to engage in a sustainable partnership platform for research and innovation on Food and Nutrition Security, and Sustainable Agriculture (FNSSA). The FNSSA roadmap facilitates the involvement of stakeholders for addressing and linking research to innovation dealing with food security issues. In this context, the LEAP4FNSSA project supports the driving of the roadmap. Research and innovation activities were captured in different data, i.e. LEAP4FNSSA database and heterogeneous textual data including project reports, websites, scientific publications, workshop reports and student theses. The Knowledge Extractor Pipeline System (KEOPS) was implemented to support the processing and analysis of textual data associated with FNSSA activities. KEOPS is based on the LEAP4FNSSA lexicon presented in this data paper. The LEAP4FNSSA lexicon composed of 331 keywords associated with 12 concepts of the food security domain is the result of 3 steps of work and brainstorming. The lexicon enables the capturing of research and innovation topics dealing with food security and conducted by African and European partners. This data paper presents the obtained lexicon and a summary of the method to build it.

©

Value of the Data

• This dataset contributes to the available resources for Natural Language Processing (NLP) and data mining on specialized domains and more precisely in the field of food security. • This dataset is useful for computer scientists for enriching thesaurus and ontologies.

• This dataset can be used for indexing data bases (for instance these keywords could be proposed as metadata). • This dataset can be used for analysing textual data dealing with agricultural sciences and social sciences. • This list of keywords can be used as part of a search strategy protocol for systematic review research in areas related to food security.

Data Description

In order to analyse textual data dealing with food security we have to consider different topics related to this issue. The proposed lexicon takes into account the multifactorial aspect related to food security with 331 keywords associated with 12 concepts summarized in Table 1 . Examples of the concepts "food security" and "water management" are given in Tables 2 and3 . Note that both examples represent only 2 out of 12 concepts. All these concepts refer to different aspects of food security and sustainable agriculture in Africa and Europe. The 12 concepts are given in the Dataverse repository: https://doi.org/10.18167/DVN1/D1C53L .

Experimental Design, Materials and Methods

The LEAP4FNSSA lexicon is the combination between 3 semantic resources, i.e. inputs in order to construct the final lexicon:

• Pretoria vocabulary (list 1) : This first lexicon composed of 8 concepts has been obtained during a workshop organised in Pretoria in 2019 in the context of the LEAP4FNSSA project.

The process and the lexicon obtained are described in [START_REF] Roche | PRETORIA lexicon -CIRAD Dataverse[END_REF][START_REF] Roche | KEOPS -LEAP4FNSSA -Indexing -CIRAD Dataverse[END_REF] • Agrovoc vocabulary (list 2) : Based on these 8 concepts (with one additional concept), Agrovoc terms associated with these concepts are manually extracted from the online 1 resource. Agrovoc is a multilingual thesaurus dedicated to the agricultural domain devel-oped by FAO (Food and Agriculture Organization) [START_REF] Caracciolo | The AGROVOC linked dataset[END_REF] . This thesaurus is used for different applications, e.g. indexing, annotation, data linking, etc. • Terms obtained by text-mining (list 3) : Terminology is extracted from the LEAP4FNSSA corpus using generic parameters of the BioTex tool [START_REF] Lossio-Ventura | Biomedical term extraction: overview and a new methodology[END_REF] . The LEAP4FNSSA corpus consists of documents and web pages relating to the FNSSA project database2 . BioTex uses both statistical and linguistic information to extract terminology from free texts. The process applied is described in [START_REF] Martin | Keops: Knowledge extractor pipeline system[END_REF] .

The initial terms (i.e. Pretoria vocabulary, Agrovoc vocabulary, terms obtained by text-mining) are given in the document 'LEAP4FNSSA_LEXICON_method_v2.pdf' available in the Dataverse repository: https://doi.org/10.18167/DVN1/D1C53L .

The LEAP4FNSSA lexicon is obtained with 3 iterative steps. In these different steps, 4 types of experts and skills were involved: research scientist in text mining 3 , IT engineer 4 , experts in database indexing 5 , experts in food security issues (i.e. members of the LEAP4FNSSA project).

1. The first step based on the three inputs (i.e. lists 1, 2 and 3 ) involves the actions summarized below:

• Starting point: the Agrovoc vocabulary (i.e. list 2 ) with 9 initial concepts and terms associated with FNSSA. • Based on a survey dedicated to Work Package 3 members of the LEAP4FNSSA project (10 answers), a term associated with 2 or more irrelevant labels is removed (strict pruning). Irrelevant labels are assigned by the LEAP4FNSSA members according to the point-of-view of their work and expertise. • For each concept, the Pretoria terms (i.e. list 1 ) are added to obtain a new lexicon.

• The irrelevant terms of this new lexicon (based on a survey with 12 answers) are removed (strict pruning applied). • New terms proposed from surveys and brainstorming are added (i.e. LEAP4FNSSA workshop). • Selection of terms extracted by text-mining (i.e. list 3 ) labeled as relevant by Work Package 3 members (via a survey with 5 answers). • Final suggestions from the surveys are taken into account (e.g. remarks, new concepts, concepts to delete). 2. The second step is based on the following process:

• Starting point: the lexicon obtained at step 1.

• Improvement of concepts:

• The 'Project management' concept is deleted because this concept is not a major focus of the LEAP4FNSSA project and food security issues. • The 'Agroecology' concept is added with terms proposed by Work Package 3 members. • Improvement of terms:

• Terms are manually lemmatized.

• Animals are added in the 'Agriculture and animal production' concept.

• Diseases are added in the 'One Health' concept. 3. The last step is summarized below:

• Starting point: the lexicon obtained at step 2.

• Improvement of concepts:

• Names of specific concepts have been changed.

• Two new concepts are added: 'Food value chains and market' and 'Agricultural systems'. These concepts contain new terms and terms that come from other concepts.

• Improvement of terms:

• New keywords are added after a work conducted by the experts in charge of data indexing of the FNSSA project database. For instance, keywords extracted from the FNSSA project database and manually validated by the experts are added. • Some terms are swapped between different concepts.

• Ambiguous terms are deleted (e.g. capacity, agriculture, etc.) • The word 'crop' is deleted in the 2-word terms of the 'Crops' concept.

• New keywords are integrated after a final checking by the experts in charge of data indexing.

These modifications to consolidate the LEAP4FNSSA lexicon (e.g. addition and/or deletion of concepts and/or terms) are detailed in the document ' LEAP4FNSSA _ LEXICON _ method _ v2.pdf '.

Note that variations of terms could be automatically extracted with NLP approaches in dedicated corpora [START_REF] Bourigault | Term extraction + term clustering: An integrated platform for computer-aided terminology[END_REF][START_REF] Nenadic | Enhancing automatic term recognition through recognition of variation[END_REF] . This will be integrated as future work to extend the current lexicon.

The LEAP4FNSSA lexicon obtained is integrated into the KEOPS (Knowledge ExtractOr Pipeline System) tool that uses text mining approaches to highlight knowledge from heterogenous textual data [START_REF] Martin | Keops: Knowledge extractor pipeline system[END_REF] . KEOPS is currently implemented on LEAP4FNSSA data in order to extract, visualise and analyse food security themes with maps, graphs, curves, and Venn diagrams [START_REF] Ho | What can venn diagrams teach us about doing data science better?[END_REF] .

  2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

	Specifications Table
	Subject	Agricultural Sciences; Computer and Information Science; Social Sciences
	Specific subject area	Lexicon in English dealing with food security
	Type of data	Table
	How data were acquired	Data are manually acquired by combining 3 types of resources (primary
		source): Pretoria vocabulary (obtained during a workshop organised in Pretoria
		in 2019), Agrovoc terms ( https://www.fao.org/agrovoc/ ), and terms obtained by
		text mining. The LEAP4FNSSA lexicon is obtained with 3 iterative steps based
		on surveys and brainstorming with experts.
	Data format	Filtered (LEAP4FNSSA lexicon) and raw (description of the process to build this
		lexicon).
	Description of data collection	The dataset consists of (i) one table file with lexicon, (ii) a document
		describing the steps to obtain the final lexicon.
	Data source location	The data are hosted on the CIRAD Dataverse. The data were built in the
		context of the LEAP4FNSSA project 1 .
	Data accessibility	Repository name: CIRAD Dataverse. Data identification number:
		10.18167/DVN1/D1C53L.

Direct URL to data: https://www.doi.org/10.18167/DVN1/D1C53L

Table 1

 1 Number of keywords by concept.

	Concept	Number of keywords
	Food security	20
	Agroecology	22
	Climate change	14
	Water management	37
	Crops	61
	Livestock and animal production	26
	One Health	34
	Agricultural intensification and innovation	31
	Food value chains and market	29
	Agricultural systems	20
	Partnerships in agricultural research development	11
	Research + Training	26
	TOTAL	331

Table 2

 2 Keywords associated with the "food security" concept.

	food security	food access	food insecurity
	household food security	food aid	food sovereignty
	hunger	nutrition security	right to food
	self-sufficiency	novel food	resource management
	early warning	nutritional quality	malnutrition
	socioeconomic sustainability	sustainable intensification	sustainable food security
	urban nutrition security

Table 3

 3 Keywords associated with the "water management" concept.

	water management	flood control	freshwater management
	hydrological restoration	rain water management	water accounting
	water auditing	water conservation	water extraction
	water management in lowland	water management in upland	water security
	water supply	water treatment	water conservation zone
	drainage	hydraulic structure	water reuse
	water storage	water use	agricultural hydraulics
	watershed management	resource management	water resource
	rural planning	water exploration	water rights
	irrigation	groundwater storage	ground water storage
	water quality	water governance	water harvesting
	ict-based irrigation	drought	water constraint
	hydrological monitoring

https://www.fao.org/agrovoc/

https://www.library.wur.nl/WebQuery/leap4fnssa-projects

first author

last author

second and third authors

Acknowledgments

This work is supported by LEAP4FNSSA H2020 project, SFS-33-2018, grant agreement 817663. We thank the WP3 leaders, Petronella Chaminuka and Ioannis Dimitriou, and the WP3 members for their contribution to analyse the first results obtained.

Data Availability

LEAP4FNSSA lexicon (Original data) (Dataverse).

CRediT Author Statement

Mathieu Roche: Data curation, Methodology, Formal analysis, Writing -original draft; Agneta Lindsten: Data curation, Formal analysis, Writing -review & editing; Tomas Lundén: Data curation, Formal analysis, Writing -review & editing; Thierry Helmer: Data curation, Formal analysis, Writing -review & editing.

Ethics Statement

No conflict of interest exists in this submission. The authors declare that the work described in this paper is original and not under consideration for publication elsewhere, in whole or in part. Its publication is approved by all the authors listed.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.