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5.1 Components
As mentioned in Chapter 2, a component is a part
of the system that exists when the system is executing. For example,
the project management system may be decomposed into the following
components:
A user interface component
Responsible for providing a user
interface through which users may
interact with the system
A business-processing component
Responsible for implementing business
functionality, including all the
project management functionality provided by the project management
system
A data component
For implementing data
storage functionality
A security component
Provides various forms
of security functionality to the
business-processing and data components, including user
authentication and verifying user privileges when accessing data
Components follow the type-instance dichotomy first discussed in
Chapter 2 and applied to classes and objects in
Chapter 3. You can use the UML to talk about
classes of components as well as specific components of a class. When
speaking of a class of components, it's customary to
use the
terms component or component
class. Thus, while you might think of a component as a
specific thing, in the UML, a component really represents a class of
things. When speaking of a specific component of a class, use the
term component
instance.A component exists during execution time and requires a resource on
which to execute, which I talk about in the next section, Section 5.2. In the UML, a component is
shown as a rectangle with two small rectangles protruding from its
side. The rectangle is labeled with the name of the component class.Figure 5-1 shows various components associated with
the project management system, including user interface,
business-processing, data, and security components.
Figure 5-1. Components of the project management system
A component instance is a specific component. For example, specific
components of the project management system include:
A web user interface component instance
Allows users to access the
project management system
via the Web
A client/server user interface component instance
Allows users to access the project management system in a
client/server environment
A local data component instance
Stores project management data for a specific user or group of
users
An enterprise data component instance
Stores project management data for a complete
organization
A component instance is shown similar to a component class, but is
labeled with the component instance name followed by a colon followed
by the component class name, with all parts of the name fully
underlined. Both names are optional, and the colon is present only if
the component class name is specified.Figure 5-2 shows various component instances of the
component classes in Figure 5-1, including two user
interface component instances, named Web and
Client Server, two data
component instances, named Local
Data and Enterprise
Data, a nameless business processing component
instance, and a nameless security component instance.
Figure 5-2. Component instances in the project management system
