Basically Extensibility mechanism allows you to extend and
customize UML by adding new building
blocks, creating new properties and specifying new semantics in order to make
the language suitable to your specific problem
domain.
There are 3 Type of extensibility mechanisms:
- Stereotypes.
- Tagged Values.
- Constraints.
Stereotypes:
Stereotypes allow you
to increase vocabulary of UML. You can add, create new model elements, derived from
existing ones but that have specific properties that are suitable to your
problem domain. Stereotypes are used to introduce new building blocks that
speak the language of your domain and look primitive. It allows you to
introduce new graphical symbols.
For example: When modeling a network you might need to have
symbols for router, switches , hubs etc. A stereotype allows you to make these
things appear as primitive.
Tagged Values:
Tagged values are
used to extend the properties of UML so that you can add additional information
in the specification of a model element. It allows you to specify keyword value
pairs of a model where keywords are the attributes. Tagged values are
graphically rendered as string enclose in brackets.
For Example: Consider a release team responsible for assembling,
testing and deployment of a system. In such case it is necessary to keep a
track on version and test results of the main subsystem. Tagged values are used
to add such info.
Tagged values can also be used to add administrative info
such as author name, date modifies etc.
Constraints:
They are the properties for specifying semantics or
conditions that must be held true at all the time. It allows you to extend the
semantics of UML building block by adding new protocols. Graphically a
constraint is rendered as string enclose in brackets placed near associated
element.
For example: In development of a real time system it is necessary
to adorn the model with some necessary information such as response time.
