Military Communications and Information Technology: A Trusted ...

Chapter 1: Concepts and Solutions for Communications and Information Systems
23
sets of composite services and obtain optimal configuration from the performance
point of view.
III. Background
System performance is determined by the way a system uses resources. Different
implementations of the same functionality can have different computational
complexity. In the performance domain three basic concepts can be distinguished:
workload, resources and scenarios. Scenario describes the system’s behavior including
demands for resources. Each scenario is executed with a frequency defined by
a workload. Resources can represent software (passive resources – for example:
buffer, critical section, database connection pool) or an underlying platform (active
resources – for example: processor, disk, network).
To conduct the system performance evaluation two questions should be answered:
how the system will be documented and which performance model should
be used. In the following subsections SOA concept is described including basic elements
which should be documented allowing performance evaluation. Moreover,
notations and framework used to document SOA architecture is outlined. Finally,
the performance model is described.
A. Service Oriented Architectures
Service Oriented Architecture is a concept of an architecture that supports
interoperability, scalability and flexibility of heterogeneous systems. SOA defines
a ‘service’ concept which represents well defined fragment of an operational functionality.
Services introduce new abstraction layer between operational logic and
legacy systems used in organization increasing cohesion between them. SOA
transforms architecture style of an application into a set of connected services used
when they are considered necessary.
Abstract view of SOA can be described using layered architecture. Fig. 1 depict
high level view of layers [22].
Looking at layers presented in the diagram (Fig. 1), the most important
is the identification of processes and business services used by consumers. An operational
process describes how an organization achieves its goals. The processes
layer allows to understand an operational domain which is the object of interest
when the SOA architecture is defined. Furthermore, it allow to identify the process
activities that should be supported by services.
Services are described through well-defined interfaces. Interface definition
is independent from an underlying platform on which the service implementation
is running. This approach allows services, build on a heterogeneous
systems, to interact in a uniform and universal manner. Two types of services
can be defined: