Web Service Discovery Mechanisms Looking for a Needle in a Haystack?

Web Service Discovery Mechanisms Looking for a Needle in a Haystack?

Evangelos Sakkopoulos

joint work withJ. Garofalakis, Y. Panagis, A. Tsakalidis University of Patras, CEID& RA Computer Techonology Institute

Research Academic Computer

Technology Institute2

Overview of Talk

Introduction Description of Players Discovery Architectures Data Models Quality of Service Conclusions



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



Reasons for discovery + common problems

Why: Need for complex WS invocation

patterns Need to chose between several

descriptionsProblems: Heterogeneities in Technical,

Pragmatical, Ontological Level



Description of Players [catalogues]

Centralized repositories of WS Descriptions

UDDI – emerging protocol, v. 3.01. 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)



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)



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



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



Discovery Achitectures (3)



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



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



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



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



Data Models – A taxonomy



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.



Discovery with QoWS

Ouzzani and Bouguettaya, IEEE Internet Computing, March 2004. 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



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.

Thank you

Inquiries:[email protected]

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Web Service Discovery Mechanisms Looking for a Needle in a Haystack?