Web Services Composition

1. INTRODUCTION Nowadays many enterprises publish their applications functionalities on the Internet. This new generation of applications allows greater efficiency and availability for business. In fact, more and more applications make functionalities available using a web service format. However there are many services around the web, each one, taken alone, has a limited functionality. In many cases, a single service is not sufficient to respond to the user's request and often services should be combined through services composition to achieve a specific goal. For example, if a user wants to travel, it is not sufficient to book a flight, but she should also take care of reserving a hotel, renting a car, getting entertained, and so on. Such composition is carried out manually today, it means that the user needs to execute all these services one by one and these tasks can be time and effort consuming. For that reason, the notion of composite services is starting to be used as a collection of services combined to achieve a user's request. In other words, from a user perspective, this composition will continue to be considered as a simple service, even though it is composed of several web services. Nevertheless, prior to composing web services, candidate services should first be discovered and then selected. One difficulty is that many functionally