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

2. SEQUOIAS 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

3. SEQUOIAS 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.

4. SEQUOIAS 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).

5. SEQUOIAS 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.

6. SEQUOIAS 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

7. SEQUOIAS 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

8. SEQUOIAS 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.

9. SEQUOIAS 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

10. SEQUOIAS 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.

11. SEQUOIAS 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.

12. SEQUOIAS 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.

13. SEQUOIAS 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.

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

15. SEQUOIAS 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

16. SEQUOIAS 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

17. SEQUOIAS 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.

18. SEQUOIAS 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 depends on the constraint operator op expressed in the NFP constraint and is computed by formulas like Degree=f op (OffValue,ReqValue)

19. SEQUOIAS 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

20. SEQUOIAS 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.

21. SEQUOIAS 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.

22. SEQUOIAS 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:

23. SEQUOIAS YR-SOC'07 - Leicester 11-12 June 2007 23  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: Filtering

24. SEQUOIAS 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.

25. SEQUOIAS 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

26. SEQUOIAS 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.

27. SEQUOIAS 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.

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