Web Service Discovery Mechanisms Looking for a Needle in a Haystack? Evangelos Sakkopoulos joint work with J. Garofalakis, Y. Panagis, A. Tsakalidis University of Patras, CEID & RA Computer Techonology Institute

2 Research Academic Computer Technology Institute Overview of Talk Introduction Description of Players Discovery Architectures Data Models Quality of Service Conclusions

3 Research Academic Computer Technology Institute The name of the game Web Service (WS): interoperable S/W components that can be used in application integration and component based application development WS Discovery: requester + middle agent = find Find the WS matching certain functional criteria

4 Research Academic Computer Technology Institute Reasons for discovery + common problems Why: Need for complex WS invocation patterns Need to chose between several descriptions Problems: Heterogeneities in Technical, Pragmatical, Ontological Level

5 Research Academic Computer Technology Institute Description of Players [catalogues] Centralized repositories of WS Descriptions UDDI – emerging protocol, v SOAP APIs 2. XML representation for the registry 3. WSDL interface definitions 4. APIs Defs of various tech. models Three types of info available in UDDI White pages (contact info) Yellow pages (WS categorization) Green pages (Technological INformation)

6 Research Academic Computer Technology Institute Description of Players [P2P systems] Distributed, Load balanced repositories Typical P2P overlay Chord [Stoica et. al. 2001], Pastry [Rowstrom et. Al. 2001], CAN [Ratnasamy et. al. 2001] Several WS Discovery systems have chosen Chord as overlay WS Descriptions hashed and distributed over Chord Ring Speed-R [Sivashanmugam et. al. 2004], uses combination of Ontological mapping and P2P (nodes have different roles and are controlled by ontologies)

7 Research Academic Computer Technology Institute Discovery Architectures (1) Manual A human queries and decides Automatic Discovery by a requester agent Centralized UDDI registry: Centralized, authoritative repository of service descriptions Decentralized Distant ancestors of Whois++, rWhois systems UDDI Federations P2P systems

8 Research Academic Computer Technology Institute Discovery Achitectures(2) Following the standards: Info is added on white or yellow pages Modify green pages (design by contract) Ignoring the standards Active UDDI (a new WS for mediator) Grid Computing Industrial Standards J2EE, MS.NET, Java-based APIs

9 Research Academic Computer Technology Institute Discovery Achitectures (3)

10 Research Academic Computer Technology Institute Data Models - The IR viewpoint UDDI keyword matching = Boolean IR Model Sajjanhar et. al., 2003: Service Descriptions are modelled as texts, texts as vectors, a term- document matrix A is built LSI is applied to A Ability to query by similarity

11 Research Academic Computer Technology Institute Data Models - The IR viewpoint (cont’d) Schmidt and Parashar, 2004 WS Descriptions = d-dimensional point Hilbert curve: Points are mapped to 1-d and assigned unique IDs IDs hashed and distributed in a Chord XChord, Li et. al. P2P discovery Descriptions extracted, hashed and distributed across Chord

12 Research Academic Computer Technology Institute Data Models- The Semantics Viewpoint Desideratum: retrieve WS with similar functionality Semantic WS descriptions with DAML-S OWL-S Paolucci et. al., ISWC 2002 An ontology for each WS (Service Profile) Service Profile: Functional Attr., Functional Descr. Ontology  Subsumption and Semantic Matching Matchmaker implemented as UDDI add-on Sivashanmugam et. al., ISWC 2003 Matching engine implemented with semantic additions to WSDL descriptions

13 Research Academic Computer Technology Institute Data Models- The Semantics Viewpoint (2) Moreau et. al. 2002, Agents are described as WS Matching: structural validations of queries against XML service descriptions Hu, NODe 2002, Domain Ontologies and Operation Ontologies Binding Ontology performs matching Overhage, 2002 Blue pages, a new UDDI section with semantic descriptions

14 Research Academic Computer Technology Institute Data Models – A taxonomy

15 Research Academic Computer Technology Institute Quality of Service Concerns Quality of Web Service (QoWS): a rather neglected issue First attempt to define: Ran, 2003 QoWS parameters: Computational Behavior: Latency, Accuracy, Throughput, Availability Business Behavior: Invocation Cost, Company Reliability Metadata Constraints: Location, Company Preference etc.

16 Research Academic Computer Technology Institute Discovery with QoWS Ouzzani and Bouguettaya, IEEE Internet Computing, March QoWS parameters are categorized as negative and positive. QoS distance, measures advertised vs provided QoWS Execution plan, an ordered execution sequence of WSs. Selection performed of an optimum execution plan that maximizes provided QoWS

17 Research Academic Computer Technology Institute Conclusions Surveyed work emphasizes binding and matching. UDDI and P2P systems, the main players Data models: classical IR to Ontologies More emphasis to QoWS provisioning Discovery not only for WS, web-based S/W components, too.

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