A Semantic-Based Web Service Composition Facility for ebXML Registries Asuman Dogac Yildiray Kabak Gokce Laleci Middle East Technical University Ankara Turkey

Outline Web Services, WSDL, SOAP Why WSDL is not enough? Semantic of Web Services ebXML and the ebXML Registry Information Model How to Exploit Web Services Semantics through ebXML? A Web Service Composition Tool Conclusions

Web Services, WSDL, SOAP

Web Services Web services encapsulate business functions  Check credit card number  Payment processing  Stock quotes  Request for quote, bid processes They can be used to compose business processes  Travel planning  Health care  …

What is a Web Service? A Web Service is an interface that describes: a collection of operations that are network-accessible through standardized XML messaging To put it simply, Web services are applications that interact with each other using Web standards Web Service Client Application XML WEB

Web Services Web Service Client Application XML WEB Existing Application Existing Application Existing applications can be wrapped as Web services Client and Service can use different platforms and programming languages Services can be composed to make composite services

Web Service Model Service Registry (ebXML or UDDI) - Web service descriptions Service Consumer Service Provider - Web service - Service Description in WSDL Publish service Discover service Invoke service through SOAP

Why WSDL is not enough?

Web Service Description Web ServiceService Consumer Web Service Description defines uses

WSDL Structure Service Port (e.g. Binding (e.g. SOAP, JMS, direct call) Abstract interface portType operation(s) inMesageoutMessage Port Binding Where to access it How to access it Abstract definition of the service (set of Operations) Operation: An Exchange of Messages between a service Requestor and a Service provider

XML Messaging: SOAP The current standard for XML Messaging is Simple Object Access protocol (SOAP) Applications typically communicate with Web services via SOAP messaging Typically HTTP is used as RPC transport XML is used as RPC encoding scheme

SOAP over HTTP HTTP POST Message SOAP Endpoint Reference XML Message SOAP Payload SOAP Header SOAP Body SOAP Envelope

The SOAP Envelope <SOAP-ENV:Envelope xmlns="

SOAP Endpoint Reference /ProductCatalog#getPrice IP Host AddressTCP Port No Object Endpoint ID POST /ProductCatalog HTTP/1.0 Host: Content-Type: text/xml; charset="utf-8" Content-Length: 500 SOAPAction: ``

SOAP Envelope <SOAP-ENV:Envelope xmlns:SOAP-ENV=" SOAP-ENV:encodingStyle=" xmlns:xsi=" xmlns:xsd="

SOAP Body Palm Pilot Method Name Input Parameter

SOAP Response HTTP/ OK Content-Type: text/xml; charset="utf-8" Content-Length: 400 <SOAP-ENV:Envelope xmlns:SOAP-ENV=" SOAP-ENV:encodingStyle=" xmlns:xsi=" xmlns:xsd=" Standard Suffix

Web Service Semantics

Like their real-life counter parts, Web services have properties In order to exploit services in their full potential their properties must be defined:  The methods of charging and payment  The channels by which the service is requested and provided  Constraints on temporal and spatial aspects  Availability  Service quality  Security, trust and rights attached to a service

An Example Ontology for Travel Domain TravelService Entertainment Service Accommodation Service ReserveAFlightBuyATicket AirTransportation Transportation Service originatingFrom destinationTopaymentMethod Properties of the Generic Service Class

WSDL does not describe Web service semantics Web ServiceService Consumer Web Service Description defines Semantic description of the properties of a service uses

Taxonomies are not enough to define service semantics: An Example Taxonomy: UNSPSC Communications and Computer Equipment and Peripherals and Components and Supplies Business Transaction and Personal Business Software Tax Preparation Software

ebXML

Electronic Business XML (ebXML) Electronic Business XML is an initiative from OASIS and United Nations Centre for Trade Facilitation and Electronic Business ebXML aims to provide the exchange of electronic business data in Business-to-Business and Business-to-Customer environments The ebXML specifications provide a framework in which EDI's substantial investments in Business Processes can be preserved in an architecture that exploits XML's technical capabilities

ebXML A joint global initiative by  UN/ CEFACT – United Nations Center For Trade Facilitation And Electronic Business  OASIS – Organization for the Advancement of Structured Information Standards United Nations Center for Trade Facilitation and Electronic Business  Sets worldwide policy and technical development in trade facilitation and electronic business  Developed international EDI standard, UN/ EDIFACT The initiative leverages from the success of EDI in large businesses, and intends reaching small and medium enterprises

ebXML Architecture’s functional components Business Process Specification Schema (BPSS) Business processes are not fixed! Trading Partner Information  Collaboration Protocol Profile CPP Trading Partner Agreement  Collaboration Protocol Agreement CPA Registry/Repository Messaging Service Core Components

An Overview of Functional Components in ebXML Repository ebXML Business Process Specifications Business Document Specification ebXML Core Components CPP CPA Business Service Interface Business Service Interface ContextFor ReferenceTo BuiltWith Implement one Partner Role Implement other Partner Role

ebXML Registry 3 Register Company Information 1 Request Business Details 4 Query about Company A Company B 5 Download Scenarios and Profiles 2 Build Local System 6 Agree on Business Arrangements 7 Do Business Transactions! ebXML compliant system

ebXML Registry Information Model (RIM) RegistryObject ClassificationNodeClassification RegistryPackageExtrinsicObjectService AssociationRegistryEntry ClassificationScheme

How to Exploit Web Services Semantics through ebXML?

Exploiting semantics In relating the semantics with the services advertised in service registries, there are two key issues:  Where to store the generic semantics of the services  How to relate the services advertised in the registry with the semantic defined through an ontology ReserveAFlight originatingFrom destinationTopaymentMethod MyService TravelService Entertainment Service Accommodation Service ReserveAFlight BuyATicket AirTransportation Transportation Service originatingFrom destinationTopaymentMethod ? ?

Where to store the generic semantics of the services? An ebXML registry allows to define semantics basically through two mechanisms:  It allows properties of registry objects to be defined through “slots” and,  Metadata can be stored in the registry through a “classification” mechanism

Relating a Web service Advertised with Service Ontology ReserveAFlight originatingFrom destinationTopaymentMethod MyService How to relate MyService to a generic service class?

Relating a Web service Advertised with Service Ontology in ebXML MyService: Registry Entry ReserveAFlight: ClassificationNode ServiceToIndustryClassification: Classification classsifiedObject classificationNode

How to relate services advertised with the generic ontology classes? By relating a service advertised with a node in classification hierarchy, we make the service an explicit member of this node The service also inherits the well-defined meaning associated with this node as well as the generic properties defined for this node When we associate “MyService” with “ReserveAFlightService”, its meaning becomes clear; that this service is a flight reservation service Assuming that the “ReserveAFlightService” service has the generic properties such as “originatingFrom”, “destinationTo” and “paymentMethod”, “MyService” also inherits these properties

“SubmitObjectRequest” which declares the semantic of “MyReserveAFlightService” and relates it with the “ReserveAFlightService” …

An Example “SubmitObjectRequest” (Cont’d) Istanbul New York Credit Card

An Example “SubmitObjectRequest” (Cont’d)

Service Composition: Travel Service Example

An AdhocQueryRequest to return “ReserveAFlightService” as a composite object including the slots <AdhocQueryRequest xmlns = "urn:oasis:names:tc:ebxml- regrep:query:xsd:2.0" xmlns:xsi = " xsi:schemaLocation = "urn:oasis:names:tc:ebxml-regrep:query:xsd:2.0 query.xsd"> ReserveAFlightService

User Interface

A Filter Query Retrieving all the services classified by ReserveAFlightService Node and Originating from Istanbul ReserveAFlightService originatingFrom Istanbul …

Implementation Status A proof of concept implementation of the system is realized by using OASIS ebXML Registry Reference Implementation As an application server to host Web services to be accessed through SOAP, Apache Tomcat 4.1 is used The WSDL descriptions of the implemented services are generated through IBM Web services Toolkit 3.2 (WSTK) Finally IBM Web Services Invocation Framework 1.0 (WSIF) is used to invoke services.

Conclusions Web Services will transform the web from a collection of information into a distributed device of computation In order to employ their full potential, appropriate semantic mechanisms for web services need to be developed A semantic-based service composition tool for ebXML registries is described Service discovery and composition by using the semantics of services has been addressed in the literature where the weight of the work has been on using AI techniques to match the inputs and outputs of services requested and advertised The main problem with these approaches is the performance, which is not yet at the levels to be adopted by the industry

Conclusions In contrast to such approaches, we take a data management approach for service discovery by exploiting the meta data and the query mechanism of the ebXML registry With the tools we have provided, the registry is queried for explicit members of a classification node to obtain the generic parameters of the service and users are allowed to fill these in through graphical user interfaces generated dynamically Then the registry is queried for matching services; the corresponding WSDL files are obtained and through a workflow mechanism presented, the users can compose the discovered services The current workflow mechanism implemented is a simple one realizing basic workflow functionality As a future work, we plan to use one of the recent Web services choreography languages, such as BPEL4WS in composing the services

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