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A NOVEL APPROACH TO WEB SERVICES DISCOVERY

A NOVEL APPROACH TO WEB SERVICES DISCOVERY. Università di Milano-Bicocca. Marco Comerio. comerio@disco.unimib.it. Index. Objectives & Motivations The Web Services Modeling Ontology (WSMO) Non-functional Properties (NFPs) The NFP-based Discovery Process Conclusions and Future Works.

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A NOVEL APPROACH TO WEB SERVICES DISCOVERY

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  1. A NOVEL APPROACH TO WEB SERVICES DISCOVERY Università di Milano-Bicocca Marco Comerio comerio@disco.unimib.it YR-SOC'07 - Leicester 11-12 June 2007

  2. Index • Objectives & Motivations • The Web Services Modeling Ontology (WSMO) • Non-functional Properties (NFPs) • The NFP-based Discovery Process • Conclusions and Future Works YR-SOC'07 - Leicester 11-12 June 2007

  3. Objectives • Definition of a technique to enrich SWS requests and descriptions with the specification of non-functional properties (NFPs); • Proposal of a novel approach to a NFP-based SWSs discovery; • Test and validation of the proposal in the WSMO environment. YR-SOC'07 - Leicester 11-12 June 2007

  4. Motivations • The discovery of a Semantic Web service (SWS) is the act of locating a machine-processable description of a SWS-related resource that may have been previously unknown and that meets certain functional criteria. • The increasing availability of SWSs that offer similar functionalities requires the discovery process to be enhanced with a selection phase that considers non-functional properties (NFPs) of the SWSs. • NFPs could be quite relevant to match a service request and a service description. In fact, even if a service matches the requested functionalities, it could be unacceptable in terms of NFPs (e.g., cost is too expensive). YR-SOC'07 - Leicester 11-12 June 2007

  5. Motivations • This scenario highlights two needs: • enrichment of SWS descriptions with a well-defined set of NFPs; • enhancement of the matching functionality between SWS requests and descriptions. YR-SOC'07 - Leicester 11-12 June 2007

  6. Index • Objectives & Motivations • The Web Services Modeling Ontology (WSMO) • Non-functional Properties (NFPs) • The NFP-based Discovery Process • Conclusions and Future Works YR-SOC'07 - Leicester 11-12 June 2007

  7. The Web Services Modeling Ontology (WSMO) • WSMO is an ontology for describing various aspects related to Semantic Web Services. • WSMO consists of four different main elements: www.wsmo.org YR-SOC'07 - Leicester 11-12 June 2007

  8. The Web Services Modeling Ontology (WSMO) • Ontologies : provide the terminology; • Goals : define the problems to be solved; • Web Services : define various aspects of Web Services (e.g., Capabilities, Interfaces); • Mediators : allow the overcoming of data, protocol and process heterogeneity. They represent the main advantage of using WSMO and are of four different types: (i) wgMediator; (ii) ggMediator; (iii) ooMediator and (iv) wwMediator. YR-SOC'07 - Leicester 11-12 June 2007

  9. Index • Objectives & Motivations • The Web Services Modeling Ontology (WSMO) • Non-functional Properties (NFPs) • The NFP-based Discovery Process • Conclusions and Future Works YR-SOC'07 - Leicester 11-12 June 2007

  10. Non-functional Properties (NFPs) • NFPs can be considered to be constraints beyond the functionalities of a Semantic Web Service. • The management of NFPs is not a simple task because: • NFPs are characterized by several properties; • NFPs are of different nature; • NFPs are often inter-dependent. • Solution: address this problem by developing ontologies of NFPs (OntoNFPs) to formalize definitions, relations, dependencies, heterogeneous measurements and evaluation methods. YR-SOC'07 - Leicester 11-12 June 2007

  11. Non-functional Properties (NFPs) • Two different types of NFPs must be considered: • offered NFPs (offNFPs) to be included in SWS description; • requested NFPs, that are, NFP constraints (conNFPs) to be included in SWS requests. • ConNFPs and OffNFPs can be classified as: • Qualitative: expressed by enumerative values; • Quantitative: expressed by numeric values. • The strength of a good offered/required NFP description consists in supporting matching between requested and offered NFPs in a simple and effective way. YR-SOC'07 - Leicester 11-12 June 2007

  12. Offered NFPs (offNFPs) • OffNFPs are NFPs supported by the provider of the SWS. • The concept of NFP-policy is introduced to collect a set of OffNFPs with a SWS. • More NFP-Policies can be associated with a SWS. Each Policy has an applicability condition defined through an axiom. YR-SOC'07 - Leicester 11-12 June 2007

  13. NFP Constraints (conNFPs) • ConNFPs are requirements that the requester of a SWS wants to fulfill. • The concept of NFP-Request is introduced to collect a set of conNFPs with a Goal. • NFP-Request is introduced as a requester-side counterpart of NFP-Policy. YR-SOC'07 - Leicester 11-12 June 2007

  14. Web Service Description Goal NFP-Policy offNFPs NFP-Request conNFPs Non-functional Properties (NFPs) YR-SOC'07 - Leicester 11-12 June 2007

  15. Index • Objectives & Motivations • The Web Services Modeling Ontology (WSMO) • Non-functional Properties (NFPs) • The NFP-based Discovery Process • Conclusions and Future Works YR-SOC'07 - Leicester 11-12 June 2007

  16. The NFP-based Discovery Process • A novel approach to WS discovery that enriches the traditional UDDI-based process with the use of semantics and evaluation of NFPs. • The proposed SWSs discovery process is composed of five different phases. set up time execution time YR-SOC'07 - Leicester 11-12 June 2007

  17. Mediation • Mediation is performed at setup time and aims at defining: • mediators : matching rules for pairs of conNFPs and offNFPs stating when a conNFP is satisfied by an offNFP; • meta-mediators : mediators identifying which matching rules need to be invoked for a NFP-Request. • Mediators and Meta-mediators are logic programs written in F-logic that are processed by a deductive engine. • The result of matching is not a boolean value, it is a positive numeric value that states the degree of satisfaction of a certain constraint. YR-SOC'07 - Leicester 11-12 June 2007

  18. Matching Rules • Matching rules for qualitative and quantitative NFPs have been defined. • Quantitative matching rules for the most typical constraint operators have been defined. • The matching degree of pairs of quantitative <conNFP, offNFP> depends on the constraint operator op expressed in the NFP constraint and is computed by formulas like Degree=fop(OffValue,ReqValue) YR-SOC'07 - Leicester 11-12 June 2007

  19. Quantitative Matching Rules: Examples • Constraint operator (≥ ) : values greater or equal than a reqValue. ReqValue is a lower bound and that the higher value is better. • Constraint operator (≥ ) : values at least equal than a reqValue. ReqValue is a lower bound and the lower value is better. • if offValue>reqValue • if offValue<reqValue • if offValue=reqValue YR-SOC'07 - Leicester 11-12 June 2007

  20. Functional Discovery • Functional Discovery is the traditional SWSs discovery process. • This phase has the goal of finding a list of SWSs that totally satisfy the functionalities required by an end-user. • This phase finds a set of candidate services; each one providing the same functionality but associated with different sets of policies. YR-SOC'07 - Leicester 11-12 June 2007

  21. NFP Evaluation • NFP Evaluation is in charge of exploiting the matching rules stored in mediators and meta-mediators to compute the matching degree between a conNFP and an offNFP. • The result of the NFP Evaluation is a set of values in the range [0..n] associated with each NFP-policy of each SWS identified in the Functional SWS Discovery phase. YR-SOC'07 - Leicester 11-12 June 2007

  22. NFP Evaluation • On these results, two indicators are defined: • normalized degree (n-degree): shows if offValue matches a reqValue and is expressed by values in range [0..1] (if the result is >1 it is reduced to 1). • extra matching degree (extraMatch): it is an additional information about how a conNFP is satisfied. It is expressed by values in range [0..1], and is computed by the formula: YR-SOC'07 - Leicester 11-12 June 2007

  23. Filtering • Filtering consists in discarding SWSs with NFP-Policies that do not satisfy user minimum requirements and in computing two numeric matching indicator for each NFP-Policy. It is composed of three steps: • Mandatory NFPs-driven SWSs discarding : checks if the degree of matching is equal to 1 for all conNFPs with relevance equal to 1. Otherwise, the related NFP-Policy is discharged. • Calculus of NFP Global Normalized Value (NGNV) : for each NFP-Policy evaluates the NGNV with the following formula: • Calculus of NFP Global ExtraMatch Value (NGEV) : for each NFP-Policy evaluates the NGEV with the following formula: YR-SOC'07 - Leicester 11-12 June 2007

  24. Ranking • Ranking is in charge of sorting the policies of the SWSs on the basis of their NGNV values. • In the case of policies with the same NGNV value, their NGEV values are considered. YR-SOC'07 - Leicester 11-12 June 2007

  25. Index • Objectives & Motivations • The Web Services Modeling Ontology (WSMO) • Non-functional Properties (NFPs) • The NFP-based Discovery Process • Conclusions and Future Works YR-SOC'07 - Leicester 11-12 June 2007

  26. Conclusions • This ongoing work proposes: • an ontological model to capture the nature and relations among NFPs; • an enhancement of the discovery process with a selection phase that considers NFPs; • two indicators, NGNV and NGEV, to measure the matching degree between requested and offered NFPs, in order to be able to filter, rank and select a set of services offering the same functionality; • a set of matching rules to address the different kinds of constraints expressed by the requesters. YR-SOC'07 - Leicester 11-12 June 2007

  27. Future Works • Experimental validation of the proposed approach in the WSMO environment; • Enhance the NFP ontological model to capture the dependency relations among NFPs; • Semi-automatic generation of mediators; • Management of NFPs in SWS composition. These works are supported by the Single European Employment Market Place (SEEMP) project and the Networked Peers for Business (NeP4B) project. YR-SOC'07 - Leicester 11-12 June 2007

  28. Thank you!Questions? YR-SOC'07 - Leicester 11-12 June 2007

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