Class Diagrams

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Class Diagrams
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Class
Visibility
SomeClass
Attribute1 Attribute2 Type -Attribute3
Public Protected Private

• Operation1(para1type)Type
• Operation2()void
• Operation3()

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Class (Cont)
Abbreviated form
SomeClass
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Object
someObject SomeClass
Abbreviated form
someObject SomeClass
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Relationships between Classes

• There are four types of relationships between
  classes
• Association represents a relationship between
  two or more classes.
• Aggregation represents whole/part
  relationships.
• Composition represents whole/part
  relationships. A special form of aggregation,
  with strong ownership and coincident lifetime as
  part of whole. The parts are removed before the
  death of the composite.
• Generalization (Inheritance) represents
  generalization/specialization relationships.

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Association
Navigability
Name of association
Role of company
Multiplicity
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Association (Cont)
Association class
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Association (Cont)

• N-ary association.

Quaternary (four-way) association
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Association (Cont)
directory ? 0 or n files
Qualifier
(directory, file name) ? 0 or 1 file
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Association (Cont)

• Qualifier is a slot for an attribute or list of
  attributes on a binary association, in which the
  values of the attributes select a unique or a set
  of related objects from the entire set of objects
  related to an object by the association.
• Example (directory, file name) ? 0 or 1 file
• Qualifier is an index on the traversal of an
  association.

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Association (Cont)
(bank, account no.) ? 0 or 1 person person ? 0 or
n (bank, account no.)
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Aggregation

• A plain association between two classes
  represents a structural relationship between
  peers.
• The composite object may exist without its
  constituent objects.
• The object may be a constituent of more than one
  composite.

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Aggregation (Cont)
Whole
Part
Aggregation
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Composition

• Composition represents whole/part
  relationships.
• A special form of aggregation, with strong
  ownership and coincident lifetime as part of
  whole.
• The parts are removed before the death of the
  composite.

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Composition (Cont)
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Generalization

• A relationship between a general thing (called
  the super-class or parent) and a more specific
  kind of that thing (called the subclass or
  child).
• Generalization means the objects of the child may
  be used anywhere where the parent may appear, but
  not in the reverse.
• A child may have attributes and operations in
  addition to those found in its parent.
• A child may override the implementation of an
  operation of its parent.
• A class may have zero or more parents.

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Generalization (Cont)