The Unified Modeling Language User Guide

1
The Unified Modeling Language User Guide

• Chapter 11
• Interfaces, Types and Roles

2
Chapter 11 Topics

• Terms and concepts
• Seams
• Common modeling techniques
• Static and dynamic type checking

3
Terms and Concepts

• An interface is a collection of operations that
  are used to specify a service of a class or
  component.
• A class may have multiple interfaces.
• Each interface portrays the class is a particular
  role.
• Interfaces are used to manage complexity by
  providing a simplified view of the implementation
  class.
• Interfaces separate the specification and the
  implementation of a component.

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Terms and Concepts

• Graphically, an interface is a circle with a line
  running to the implementation class.
• An interface my optionally be a class icon with
  an ltinterfacegt stereotype.
• Interfaces have no attributes other than a
  pointer to the implementation class.
• Each interface has a(n)
• Name - a textual string used for identification.
• Operations - behaviors of the interface that, if
  shown, appear in a stereotyped class icon.

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Terms and Concepts

• Each interface has a(n) continued
• Relationships - Since an interface is a kind of
  class, it may participate in the same
  relationships as any other class.
• Role (implicit) - The face that an abstraction
  presents to the world. Interface names can be
  used to qualify role names on associations
  involving the implementation class - role
  SpecifierClass. (see figure 11-5, page 162)
• A class may use the stereotype lttypegt.
• Type classes are the same as interfaces except
  that they may contain attributes.

6
Realizations
7
Roles
8
Seams

• Seam(Websters)-The line of junction of 2 edges.
• Interfaces are used to model the seams of a
  system composed of software components.
• Seams represent lines of demarcation between the
  various software components.
• Seams (interfaces) provide well defined paths of
  communication between the software on either side
  of the line.
• As long as the interfaces remain constant, the
  implementation classes on either side of a seam
  may be freely changed.

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Common Modeling Techniques

• To model the seams in a system -
• Given the set of all classes in a system,
  identify subsets of classes that are tightly
  coupled.
• Tightly coupled classes interact extensively
  (collaborate) with each other to carry out a
  particular functionality.
• Identify the operations that cross the various
  collaboration boundaries.
• Package logically related sets of these
  operations as interfaces.
• For each collaboration, identify the interfaces
  it relies on (imports) and those it provides to
  others (exports).
• Imports are modeled as dependency relationships
• Exports are modeled as realization relationships.

10
Modeling System Seams
11
Static and Dynamic Type Checking

• Technically, once and object is created its type
  cannot be changed.
• Interfaces allow the implementation class to
  assume a variety of roles.
• This gives the illusion that an object of the
  implementation class can dynamically change its
  type to match the role it is assuming.
• Sometimes it is useful to model these type
  changes using an interaction diagram.
• See figures 11-7 and 11-8 on page 166.