UML syntax: Properties

[ronaldtse]

Properties

• Def.- A property is a special structural feature that if it belongs to a class, is an attribute.
• (However, it can also belong to an association. But more about this later).

Notation & Semantics

• An attribute is a (data) element that is equally contained in every object of a class and that is represented by an individual value in each object.
• Attributes have no identity outside the object to which they belong.
• Attributes are fully under the control of the objects of which they are part.

Proposal: (both diagrams mean the same thing -- we should only have one way of specifying this; it is only the rendering that is different)

Example Attributes
# Syntax: [visibility][/] name [:type][multiplicity][=initial value][{property string}]
#  Visibility:
#    - + public: it can be seen and used by all.
#    - -private: only the class itself can get hold of private attributes.
#    - #protected: both the class itself and its subclasses have access.
#    - ~ package: only classes from the same package can access these attributes.
#  - / symbolizes a derived attribute.
#  - Multiplicity is in square brackets (e.g. [1..*]).
#  - Default value specifies the initial value of the attribute.
#  Property string indicates a modifier that applies to the attribute:
#    - {readonly}: the property can be read but not changed.
#    - {union}: the property is a union of subsets.
#    - {subsets <property>}: the property is a subset of <property>.
#    - {redefines <property>}: the property is a new definition of <property> (overwritten by inheritance).

# Multiplicity collection classes
# ordered set {ordered}
# set {set}
# ordered list {sequence}
# {bag}

class Customer {
  -bookings: Bookings[0..*]
}

Attribute full syntax [visibility][/] name [:type][multiplicity][=initial value][{property string}]

Where:

• Visibility:

  • +public: it can be seen and used by all.
  • -private: only the class itself can get hold of private attributes.

  • protected: both the class itself and its subclasses have access.

  • ~package: only classes from the same package can access these attributes.

• / symbolizes a derived attribute.

• Multiplicity is in square brackets (e.g. [1..*]).

• Default value specifies the initial value of the attribute.

• Property string indicates a modifier that applies to the attribute:

  • {readonly}: the property can be read but not changed.
  • {union}: the property is a union of subsets.
  • {subsets }: the property is a subset of .
  • {redefines }: the property is a new definition of (overwritten by inheritance).

• Property string indicates a modifier that applies to the attribute:

  • {ordered}, {unordered}: an ordered or unordered set.
  • {unique}, {nonunique} or {bag}: a set may or may not contain several identical elements.
  • {sequence}: an ordered list (array; identical elements permitted).
  • {composite}: the property is an existence-dependent part and others.

• If the multiplicity is greater than 1, then the attribute represents a set.

• Additional information can be specified for the order (isOrdered) and uniqueness (isUnique). (see Multiplicity metamodel).

• Depending on the combination of these two pieces of information, we obtain different collection classes (see next table).

IsUnique	isOrdered	Collection Class
Yes	Yes	Ordered set {ordered}
Yes	No	Set (default)
No	Yes	Ordered list {sequence}
No	No	{bag}

class Customer {
  -booker: Booking[1]
}

class Booking {
  -bookings: Customer[0..*]
}

Examples of multiplicity collection classes

• name:String = ‘unknown’
• birthDate:Date
• radius: Integer = 25 {readonly}
• /age:Integer {age=today-birthDate}
• -versionNo:Integer
• time:DateTime::Time
• dynamArray[*] {ordered}
• name:String[1]
• firstName:String[0..1]
• firstNames:String[1..5]

[w00lf]

The full properties syntax was implemented in gem.