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SEMPLICE in brief

SEMPLICE (SEMantic Peer Layer InfrastruCturE) is an extensible P2P Infrastructure, designed and developed by Engineering Ingegneria Informatica S.p.a, for query and discovery across a semantic layer, based on domain and service ontologies, over the logical overlay network of a traditional P2P architecture.

SEMPLICE aim

The aim of SEMPLICE is to pay attention on Semantic Web and its possible introduction in Peer to Peer architecture. Combining Semantic Web and P2P paradigm, it is possible to probe the P2P network by means of more complex and expressive queries to put forward and propagate. The objective is the integration of content and service semantics, according to domain ontologies, inside a P2P architecture that represents each entity involved as a node of the network. Therefore the main activities are the definition of:
SEMPLICE Layers
  • a technology for services and distributed resources discovery, based on semantic description of each peer,
  • an efficient and scalable algorithm for peer selection and request routing.
In order to achieve these goals each peer should be characterized by an explicit semantic description of provided services and its own competence/knowledge, according to shared ontologies. The above considerations bring to the definition of a logical network layer based on domain and service ontologies: precisely, the definition of a P2P network of nodes that provides services described by semantic annotations, characterized by a semantic layer over the logical overlay network of traditional P2P architectures and that enables to group and forward the requests towards peers semantically similar, in an efficient manner, according to service and competence description. The advantage of this approach is on request forwarding; precisely the request is not forwarded to all peers or to a random subset of them, but only to peers with a good probability to be able to response to service request.

SEMPLICE Architecture

SEMPLICE architecture, defined by Engineering Ingegneria Informatica S.p.a, is made up of three main layers:


The lower layer, P2P Infrastructure is, to all intents and purposes, the logical overlay and network layer of traditional P2P architecture: it is the base layer of SEMPLICE system. It covers all communication activities such as network access, nodes connection and request propagation across the network.


The second layer, Semantic Layer , takes care all network semantic issues, beginning from the clustering activities, to the definition of the procedure of peer registration to the network according to its semantic description, from request propagation according to its semantics, to semantic matchmaking of services and/or resources. This layer is in a strictly contact with the above logical layer, during the peer cluster association phase, and takes into account network issues such as network balance and full connection among peers.

SEMPLICE ARCHITECTURE

The SEMPLICE Semantic Layer is composed by several modules that provide the following semantic functionalites.


The Semantic Similarity module calculates the type and degree of similarity between concepts of common domain ontologies described in OWL.


The Peer Clustering module, starting from domain ontology partition, defines the set of concepts of each semantic cluster and the way to assign each new peer to several clusters according to its semantic description. The module invokes semantic similarity module and executes a semantic match algorithm between set of concepts in order to generate a ranking of candidate clusters, even taking into account network balance issues.


The Semantic routing and discovery is the module which enables the discovery of peers and the propagation of request according to its type and semantics. Each Peer is able to discriminate the type of incoming request , to execute the relating response behavior and to propagate it in a semantic-aware manner.


The Service Matchmaking module produces the ranking of services candidate according to the type and degree of semantic match between each service candidate and the description of an abstract service to search for. The semantic match is based on IOPE (inputs outputs precondition and effects) of service description, expressed in a first release in OWLS but, in future works, in a WSDL enriched with semantics annotations (WSDL-S or other ad-hoc semantic markups).


The highest architecture layer, the SEMPLICE Peer Service Interface manages the end user peer service invocation, request formulation, discovery and request responses browsing.

SEMPLICE Node

Descriptions, semantic annotations and relations among peers, resources and services are saved in distributed registries and their interfaces are provided by/for each peer. Each registry is both a registry of metadata and a repository of content. A typical registry implementation uses some form of persistent storage such as a database to store its metadata and content. Architecturally, registry is distinct from the repository. All access to the registry as well as repository is through the operations defined by the Registry interface and by Peer Service Interface in P2P discovery context.


Each SEMPLICE node implements entirely or in part the three architectural layers. All peers implement the P2P Communication Channel by means the P2P Infrastructure in order to access the semantic net and the Peer Service Interface in order to enable end user to access Peer service discovery via Peer Web-Client or UI-Client . The Semantic Layer modules are installed according to the nature of peer: request sender (edge), semantic net access node or request respondent/propagator.