elektronická verzia publikácie - FIIT STU - Slovenská technická ...

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