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or other devices as part of the normal usage of the applications, rather than having to be installed
or deployed to each client device. This leads to tremendous optimization of TCO by obviating
the need for deployment or upgrade of the client devices whose total number across the enter-
prise could run into hundreds or thousands. Unlike client components that are mainly focused
on the GUI, server components exist primarily to provide business functionality. Examples of
server component models are Microsoft COM, Sun's Enterprise JavaBeans, and OMG's CORBA
component model.
Enterprise components run within the contexts of supporting frameworks called
containers
.
Containers provide standard infrastructural services to running components such as state manage-
ment, persistence management, security, and transaction management. This reduces the burden
on the application developers and enables them to focus on implementing business logic rather
than intricate code that supports basic application support infrastructure. Again, containers are
also classified into client and server containers. Web browsers are examples of client containers as
are the traditional Web servers that worked with CGI-BIN, HTTP, HTML, servlets, and so on.
Application servers are examples of server containers as are object-oriented databases or object
stores with their object/relational mapping tools, object request brokers (ORBs), and transaction
monitors.
In addition to the requirements of the distributed applications stated earlier, application serv-
ers may also variously provide
◾
Openness
◾
Interoperability
◾
Scalability
◾
Availability
◾
Configuration control
◾
Management (administration, configuration, deployment, etc.)
10.1.3.2 Enterprise Component Architecture
Enterprise component architecture is a high-level description of the major components of an enter-
prise and the relationship between them. Enterprise component architecture defines the enter-
prise's design (patterns and constraints) and infrastructure for components as well as defines how
compliant components are built and how they interact, how components are stored and cataloged,
and how components are located and reused.
Enterprise architecture is subdivided into two parts, namely, functional layers and distribu-
tion tiers; they can also be seen as the specification and implementation architectures, respectively.
Functional layers specify application-level responsibilities and address specific application require-
ments with specific solutions, while distribution tiers address more general set of requirements or
services that are mapped to a distributed computing system or infrastructure.
Here are characteristic features of enterprise component architecture:
1.
Separation of perspectives
: The development of distributed component architectures entails
many separate perspectives ranging from design, development, deployment, and execution.
Each of these perspectives highlights select aspects of the required architecture. Separation
of perspectives entails dividing the enterprise into a set of related but quasi-independent
subarchitectures that focus on a set of related aspects of distributed, N-tier, technology-
independent, and changeable architecture.
