elektronická verzia publikácie - FIIT STU - Slovenská technická ...
elektronická verzia publikácie - FIIT STU - Slovenská technická ...
elektronická verzia publikácie - FIIT STU - Slovenská technická ...
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168 Selected Studies on Software and Information Systems<br />
services for our goal. Although, a lot of services realizing different functions exist, it is not<br />
guaranteed that we find such one for solving our problem. This can have several reasons.<br />
One is that there are no available services for the problem domain. Another reason is that<br />
the given user’s goal is very complex and no individual service can solve it. Here, Semantic<br />
web service composition tries to bring resolution. The aim is to combine several services<br />
and arrange them in such a way, that these services deal with certain parts of the problem,<br />
to create intermediate data and to bring together a solution.<br />
The idea of Semantic web service composition is nice and there already exist methods and<br />
implemented tools to realize it. Despite of this, current solutions for automatic composition<br />
are unmature to be used in practice for variety of problems in different domains. These<br />
problems are also discussed in this document.<br />
The aim of our work is to deal with Semantic web service composition problem. We<br />
want to examine how a user can help when solving them. There already exist approaches<br />
including the user in this process. Our focus is to extend these approaches and investigate<br />
the benefit of user collaboration to define its goal, compose and execute the service. This<br />
document presents an overview of the interested area. This includes primary the Semantic<br />
web service composition and related topics.<br />
6.1 Towards Semantic Web Services<br />
6.1.1 Service Oriented Architecture<br />
Service oriented architecture (SOA) is an architectural design pattern relying on serviceorientation<br />
as its fundamental design principle [31, 32, 33]. There exist numbers of domains<br />
where systems benefit from the advantages of SOA. In [27] the authors describe an application<br />
and explains how SOA helped to meet the business needs of a credit card issuer with<br />
particular challenges. In [25] an framework for developing a component-based distributed<br />
simulation and executing the simulation in service-oriented architecture on the GRID is<br />
proposed.<br />
One of the most characteristic advantages of SOA is the principle of loosely coupling<br />
between the service provider and a consumer. SOA allows building systems from components<br />
providing their encapsulated functionality in services to each other and have minimal<br />
dependencies between themselves.<br />
Services can be divided into two categories: stateless and stateful. Stateless services do<br />
not store state information between requests. This makes the service more reliable because<br />
the recovery from partial failure is relatively easy. Stateful services require both the customer<br />
and the provider to share the consumer-specific context. This reduces the overall scalability<br />
of the services and increases the coupling between the consumer and provider.<br />
Figure 6-1 presents the stack and the elements of SOA. The stack is divided into two<br />
parts. First, it contains the functional aspect and second, the quality of services aspect. The<br />
functional aspect includes the transport component responsible for transferring the messages<br />
between the service consumer and the requester. The service communication protocol is an<br />
agreed mechanism for interaction. Service description is used to define what the service is<br />
and how it should be used. The service describes an actual service which is made available<br />
for use. Business process is a collection of services invoked in a particular sequence to meet<br />
the business requirement. The service registry is a place where the providers can publish