Component diagram

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Component diagram A component represents a
modular piece of a logical or physical system
whose externally visible behavior can be
described much more concisely than its
implementation. Components do not depend directly
on other components but on interfaces that
components support. A component in a model can be
replaced by another component that supports the
proper interfaces, and a component instance
within a system configuration can be replaced by
an instance of any component that supports the
same interfaces.
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Components (because they are classes) have
interfaces they support (provided interfaces) and
interfaces they require from other components
(required interfaces). The use of named
interfaces avoids direct dependencies among
components. This facilitates easier substitution
of new components.
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A component diagram shows the network of
dependencies among components. The component view
can appear in two forms. It can show a set of
available components (a component library) with
their dependencies this is the material out of
which a system can be assembled. It can also show
a configured system, with the selection of
components (out of the entire library) used to
build it. In this form, each component is wired
to other components whose services it uses these
connections must be consistent with the
interfaces of the components.
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A component icon is drawn as a rectangle with two
small rectangles on its side. A component is
drawn as a rectangle with a small component icon
in its upper right corner. The rectangle contains
the name of the component. A provided interface
is drawn as a small circle connected to the
component by a line. A required interface is
drawn as a small semicircle connected to the
component by a line. The figure below shows an
example.
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Components may have ports. Messages received on
different ports are distinguishable by the
component and may be implemented differently. A
port is shown by a small square on the boundary
of a component symbol. Interface symbols may be
attached to a port. Components may contain other
components as their implementation. The "wiring"
of two components in an implementation is shown
by nesting the circle of a provided interface in
the semicircle of another required interface in a
"ball and socket" notation.
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