The Existing Composition Approaches

Published Date: 02 Nov 2017

Abstract :

Service oriented architecture(SOA) change the whole situation to connect or consume resources available on web. Web Services are the most suitable example of SOA. The power or quality of provided by SOA not only lies in a web service. But by composing them in

The web has been changed a lot after the introduction of an Service Oriented Architecture(SOA). The business processes are more efficient to perform a task by composing the number of web services. But, all these things are done statically. They are not flexible in nature. Semantic web comes here to rescue. Semantic Web Service(SWS) is the form of Semantic Web. Semantic Web Service(SWS) allows services to be discover and execute them at runtime. The purpose of this paper is to compare SWS composition approaches.

Introduction :

Service Oriented Architecture(SOA) has brought revolution, the way resources or knowledge is shared on to the web. It is far better than the traditional client Server Architecture

Web Service is the best suited example of SOA.

Most of the Web Applications today, are developed as a Web Service. For almost all things, Web Service is available. Even for the same purpose multiple implementation are available. And to deal with such situation with traditional techniques like WSDL, UDDI etc. is not enough. As the growing number of implementation, it is very difficult for manual discovery and some time composition.

To tackle this issue, Web services are proposed with semantic enhancement. Three major efforts (i.e. OWL-S, WSMO and WSDL-S) are going on addressed this enhancement. The SWS community has presented some approach or solution, so that automatic composition and integration of web services is possible.

SWS Effort

Semantic web offers various machine understandable semantic description to facilitate automatic and efficient selection of service. Hence services on the web able to find each other by matching their requirements and needs. Semantic web Service will improve the discovery, composition and interaction among them with Services. It also helps to build up more complex workflows. As shown in figure the semantic web is attach to web service (or SOA) to come up with the new Semantic Web Service(SWS).

Semantic Web is the approach to facilitate machine understandable description and to consume it. By combining this capabilities to Web service, Web services can now search automatically best suited and optimal implementation. As we no longer tied to a specific implementation. By doing this, we can also protect our System from crash, when a given service is not available.

Semantic web uses Resource Description File(RDF) to describe the resource or we can say web service. This RDF files are nothing but the pointer to other RDF file. This files are being used because this file have data merging feature even if the underlying schema does not matched.

<rdf:RDF

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:si="http://www.example.com/rdf/">

<rdf:Description rdf:about="http://www.publisher.com">

  <si:title>Book Name</si:title>

  <si:author>Author Name</si:author>

</rdf:Description>

</rdf:RDF>

C:\Users\Lenovo\Desktop\Disseration\Paper\data model_graph.jpg

The Web Ontology Language for Services (OWL-S) is an ontology built on the top of OWL to describe web Service. It’s a set of markup language constructs that can be used to define properties and capabilities of Web services in a way that computer understands. It main goal is to provide a semantic description of Web service to provide facilities like dynamic and automated discovery, invocation and composition of Web Service. OWL-S provides Web service semantics by ontologically annotating: (1) the input to a Web service (2) the output produced by a Web service, (3) pre-conditions, that is required to perform a service and (4) Final outcome that the service will produce after its execution. OWL-S is a stack of OWL ontologies (Profile, Process Model and Grounding ontologies). The Process Model ontology can be used to model the composition of SWSs by defining the control flow and data flow on the basis of matching semantics of sub processes.

One more option for SWS is WSDL-S. WSDL-S approach extends tags of the existing Web Service Description Language (WSDL), instead of defining separate ontologies to provide service semantics. It not only support input/output annotation, but WSDL-S extension also enable the description of precondition and effect of a Web service operation. Sample snippet of WSDL-S is shown below :

<wsdl:message name="CarRequest">

<wsdl:part name="inO" type="tnsl: TypesOfAvailableCars"

LSDISExt:onto-concept="LSDISOnt:Roadster"/>

</wsdl:message>

WSMO is another candidate to develop specifications for SWSs. It has three approaches to model Web services composition (i.e. state machine, structured and data flow models). State-based model is some how related to WSFL in which each state defines control flow to control activities. Structured model is based on structured design methodology. It is used in workflow languages (e.g. BPEL). Data flow model is based on parallel programming languages. And it is based on concurrent control components of structured model.

Existing Composition Approaches

A Bottom-Up Approach.

The work discussed in [3] presents a bottom-up approach by integrating the semantic Web technology into Web service technology. It considers BPEL as a composition technique of Web services. The main goal is to add semantic in BPEL that provide machine understandable or semantic description of required web services within process and extending workflow execution engine (BPWS4J) to realize these semantic description. With the help of these semantic description of service the bottom-up approach uses Semantic Discovery Services(SDS) to Dynamically discover a desired service on the basis of matching semantics and bind it within composition. If in case a single service does not meet a service requirements, SDS uses a recursive back-tracking algorithm to determine a sequence of service invocation or a service chain, which takes input generated by BPWS4J and returns the output which is expected to be generated by BPWS4J. The major limitation of this approach is that the performance or efficiency decreases as the number of service profile increases in service chain. The disadvantage of this approach is that it does not consider any condition for discovery and composition purposes.

METEOR-S Approach.

In the METEOR-S project[12], a tool which is developed for dynamic composition of Web services. The METEOR-S tool or METEOR-S process designer allows process designers to design processes on the basis of constraints which are required to form a process. Constraints can be on the basis of business and processes. The main idea behind this Web Service Composition Tool is to write required service specification as an abstract process in BPEL process and to discover service whose semantic description matches to defined abstract process. Once desired services are discovered, candidate services are selected on the basis of process constraints given. Here, BPEL is used for process modeling. The major drawback of the approach is that user has to select services which were discovered dynamically manually from the bundle of services returned.

Template Based Composition.

This is an AI approach. In [5], author has used workflow template to write abstract activities. These abstract activities can be used to describe required services. On the basis of these specifications required services can be discovered to have executable workflows. This approach focuses on importance of adding preferences in templates so that services can be ranked to find most suitable one from the bunch of discovered services. Author proposes the use of semantic Web technology (OWL) for writing template so that it allows reasoning for flexible and more consistent selection of required services. This approach focuses on extending existing OWL-S process ontology to include abstract processes. This approach proposes that process ontology should have abstract process that can be used to refer to the Profile ontology of an OWL-S service with other specifications that can be used to rank and find best matching service.