Semantic Description of Web Services Thabet Slimani CS Department, Taif University, P.O.Box 888, 21974, KSA Abstract syntaxes) and in terms of the paradigms proposed for The tasks of semantic web service (discovery, selection, employing these in practice. composition, and execution) are supposed to enable seamless interoperation between systems, whereby human intervention is This paper is dedicated to provide an overview of these kept at a minimum. In the field of Web service description approaches, expressing their classification in terms of research, the exploitation of descriptions of services through commonalities and differences. It provides an semantics is a better support for the life-cycle of Web services. understanding of the technical foundation on which they The large number of developed ontologies, languages of are built. These techniques are classified from a range of representations, and integrated frameworks supporting the research areas including Top-down, Bottom-up and Restful discovery, composition and invocation of services is a good Approaches. indicator that research in the field of Semantic Web Services (SWS) has been considerably active. We provide in this paper a This paper does also provide some grounding that could detailed classification of the approaches and solutions, indicating help the reader perform a more detailed analysis of the their core characteristics and objectives required and provide different approaches which relies on the required indicators for the interested reader to follow up further insights objectives. We provide a little detailed comparison and details about these solutions and related software. between some approaches because this would require Keywords: SWS, SWS description, top-down approaches, addressing them from the perspective of some tasks bottom-up approaches, RESTful services. supported with Semantic Web Services descriptions (i.e., discovery, invocation, composition, etc) and would also require taking into account the frameworks and developed 1. Introduction applications. SWS research has as an objective to combines the services The remainder of this paper is organized as follows. Section with the aim to achieve given goals. Based on goal 2 introduces some principles for Semantic Web Service descriptions and descriptions of available services, a approaches and present in brief the vast popular of those complex service yielding the desired result is composed that have been proposed over the years classified into top- automatically. SWS research represents a new line of down, bottom-up, and Restful approaches. In Section 3 we research on service descriptions and their exploitation. The provide some information whereupon one could make a annotation of services with a description using a formal more efficient comparison and specified evaluation. This ontology to express their precise mathematical meaning section also provides an organized perspective over the represents the basic idea of services description in the state of the art in Semantic Web Service approaches that context of the Semantic Web. can better help understand the evolution of the field. Finally, section 4 provides a conclusion and perspectives The use of semantics is very useful to enables rich support for future works. for handling services. Furthermore, the use of ontologies to annotate services allows a higher degree of automation (describes the services in more formal detail). 2. Classification of semantic Description of Web Services The main goal of Semantic Web Services approaches is the automation of service discovery and service compos ition The existence of interoperable set of technologies for in a SOA [1]. communication is required for Internet-scale distributed computing. There are currently two major alternative In the last decade, several approaches have been proposed directions in these technologies, named “WS-*” and in the literature and these approaches differ in terms of the “REST”. The WS-* set of specifications uses the formalizations and implementations (Ontology language messaging paradigm and specialized service interfaces, with standardized infrastructure protocols (e.g. for security, transactions etc.). The REST direction relies on the semantic differences as much as possible. As example of e- architectural style of the World Wide Web and it views government application, administrative organizations can Web services as sets of resources accessible through the be located at the bottom of the hierarchy which recommend uniform interface of HTTP. WS-* technologies are mostly and share interoperability methods and resources from deployed within enterprises (and behind firewalls), while their point of view; and furthermore, the centralized the public Web is an increasingly large repository of direction is only accepted when there is agreement on all RESTful services. lower levels. Web services in the semantic web are enhanced using rich As a Web service domain, we consider both commercial description languages based on Description Logics (DLs) and governmental Web services. A case study based on such as the Web Ontology Language (OWL). However, analysis of 493 commercial and 96 governmental Web web services that have been enhanced with formal service operations has been conducted in the work of semantic descriptions is the definition of semantic web Kungas and Matskin., 2006 [2] and the result of the services. We distinguish two tested and validated analysis of the interaction between commercial and approaches for WS-* technologies in addition to the governmental Web services turned out that while approach based on REST technologies: Top-Down and ontologies enhance the usage of the commercial Web Bottom-Up approaches for semantic web services. Top- services, they have no significant impact on the down approaches are related to the development of governmental Web services. However, ontologies facilitate semantic web services and are based on the definition of automation of semantic integration of commercial Web high‐level ontologies providing expressive frameworks for services with governmental ones. Based on this analysis, describing Web services. On the other hand, bottom-up we say that TOP-Down approaches are useful when we models, have been adopted an incremental approach that faced with commercial Web services use. includes semantics to existing Web services standards by Additionally, this idea is confirmed by the work presented adding specific extensions which connects the syntactic in [3] which says that the existence of a web services definitions to their semantic annotations. Furthermore, the description in a machine-understandable fashion is bottom-up approach represents an extension of existing expected to have a great impact in areas of e-Commerce and standards and technologies including semantic Enterprise Application Integration (EAI). annotations rather than the entirely services modeling In the remainder of this section, several languages have based on ontologies. been presented and classified. If the technical or engineering point of view of a system or an organization seems to be clear and well proved through WS description Approaches the history of technology dissemination, then the “top down” strategy is adopted: when all parameters are defined in detailed manner, before implementation, then systems operation works out best. This is the conceptual model for any top down strategy and as application it may be applied Semantic approaches Other Approaches to e-government interoperability. As example of e- government application, a powerful administrative organization can be located at the top of hierarchy (e.g. a national government or its agency) and advises the WS-* Approaches interoperability methods and resources to be applied by all REST Approaches the actors on lower levels, supplements may be made on lower levels respectively. TopDown Bottom-Up TopDown Bottom-Up The bottom up strategy is adopted if everyone concerned bring in his/ her requirements and specifications, and we will find a solution for achieving interoperability within the Fig. 1 WS description approaches taxonomy. network which is acceptable for all involved, based on these requirements. For example, if local administrative organizations publish their services interfaces and use his/her individual ontologies, then some joint or mutual service should resolve some technical, syntactic and 2.1 Approaches Using WS-* Technologies binding and invocation of services [7]. The framework is based on DIANE Service Description 2.1.1 Top-Down Approaches (DSD) and a specialized ontology language for describing service elements called DIANE Elements. DIANE elements exploit the notions of The term Top-Down means that semantic web services are attributes, and reuse the clean separation between written directly in a formal language and don’t have any schema and instances promoted by description dependence to any non-semantic web services. All logics. Furthermore, special constructs are semantic web services technologies should be able to included in DIANE elements to describe service connect with non-semantic web services (called such as declarative and fuzzy set as well as grounding) in order to enhance any web service system variables. development. The ability to build new SWS with no SWSO: The Semantic Web Services Ontology relation to the classic web services technologies is the (SWSO) is a part of SWSL language [8], which needed features that should characterize this approach. includes formal conceptual