B. Automatic composition of semantic web services

With the growing number of Web services, importance of composing existing Web Services into more complex services in order to achieve new and more useful solutions is increasing. However, in order to automatically compose new services, existing services ne

Automatic Composition of Semantic Web Services*

Ruoyan Zhang, I. Budak Arpinar, and Boanerges Aleman-Meza

Large Scale Distributed Information Systems (LSDIS) Lab Computer Science Department, University of Georgia

Athens, GA 30602-7404, budak@cs.uga.edu

Abstract

With the growing number of Web services, importance of the dynamicity (or adaptation) of the composition. In an automatic composition, a user is not involved instead the system defines control and data-flow by assembling composing existing Web Services into more complex services in order to achieve new and more useful solutions is increasing. However, in order to automatically compose new services, existing services need to be encoded in a machine understandable form. The semantics of a service can be described by annotating it with respect to service ontologies. The goals of automatic composition include reducing the complexity of creating composite services as well as choosing an optimal composition among possible options. This paper describes the Interface-Matching Automatic Composition technique that aims for generation of complex Web Services automatically by capturing user’s expected outcomes when a set of inputs are provided; the result is a sequence of services whose combined execution achieves the user goals.

Keywords: Web Services, Composition, Semantics

1. Introduction

In recent years, a growing number of Web Services (WSs) have emerged as the Internet develops at a fast rate. The Web is now evolving into a distributed device of computation from a collection of information resources [Fensel02]. Furthermore, the need for composing existing WSs into more complex services is also increasing, mainly because new and more useful solutions can be achieved. However, the composition of discovered services and enabling data-flow among them are usually done manually, which are highly inconvenient, especially for more complex compositions.

Our service composition technique aims for reducing the complexity and time needed to generate, and execute a composition and improve its efficiency by selecting the best possible services available at the current time. In general, there are four different dimensions for a service composition: (i) degree of user involvement in a composition definition, (ii) if the composition is based on a template or actual service instances, (iii) dynamicity of the composition, and (iv) degree of user involvement in

*

This work is supported by University of Georgia Junior Faculty Grants.

inpidual services. This is very challenging due to difficulty of mapping user needs to a collection of correlated services where their interim outputs can satisfy each other’s input requirements and the final deliverable meets the user demands. Besides that, in each of these composition options either actual service instances or some generic templates are assembled. In the latter, inpidual services are searched and integrated automatically at execution time for a given plan [Chandrasekaran03].

In a dynamic composition (either user-defined or automatically-defined based on instances or templates), the composition itself can be adapted mainly because of quality of service (QoS) requirements at run-time by a user or automatically (i.e., user-adapted or automatically-adapted). Finally, a composition may not be defined at design-time but can be assembled service by service at execution time.

2. Related Work

A composition can be based on templates. An example is a trip planner, which is declared as a state chart, and the resulting composite services are executed by replacing the roles in the chart by selected inpidual services [Benatallah02]. The ICARIS project [Tosic01] and [Narayanan02] also use pattern composition approach. METEOR-S platform provides a comprehensive framework for semantic Web services and their composition [METEOR-S03]

The instance composition approach is to generate a composite service plan out of existing services. In this category, [Mao01] proposes a composition path, which is a sequence of operators that compute data, and connectors that provide data transport between operators. The search for possible operators to construct a sequence is based on the shortest path algorithm on the graph of operator space. However, [Mao01] only considered two kinds of services – operator and connector with one input and one output parameter (which is simplest case for service composition). Also in the instance composition category,

With the growing number of Web services, importance of composing existing Web Services into more complex services in order to achieve new and more useful solutions is increasing. However, in order to automatically compose new services, existing services ne

SWORD uses a rule-based expert system to determine if a plan of composite service can be built out of existing services [Ponnekanti02]. It mainly focused on the composition of information provider services (i.e., not world-altering services), and (like [Mao01]) it does not address the input and output mismatch problem. In our approach, services can have more than one input and output, and these parameters can mismatch in the composition process.

3. Modeling Semantic Web Services

A Semantic WS is a unit of composition that can be deployed independently, and may be subject to composition by a third party on the Web. At the same time, its interface, its process specification (i.e., its functionality) and its relations to other services are defined, and advertised in a machine-processable form so it can be automatically disc …… 此处隐藏：16334字，全部文档内容请下载后查看。喜欢就下载吧 ……