| Previous | Table of Contents | Next |
Associations constitute a relationship between two classes, and can appear in two forms: either containment relationships
or non-containment relationships. Further to
this, classes can contain references into associations (see 6.5, “Reference
Representations?). This leads to three methods of representing the link between
associated class instances.
Firstly, if one or more of the classes participating in the association contains a reference into the association, then the
elements participating in the association can be displayed within the representation of the class containing the reference,
as described
above in 6.5, “Reference Representations.?
Secondly, if the association represents a containment relationship, but there are no classes with references to the association,
the association contents may be displayed within the representations of the containing class instances. The representation
for the contained instance is exactly the same as if it were referenced, except that the name of the association is substituted
for the name of the reference. This is shown by the
production rules in 6.3, “Class Representations.? The association name is optionally
displayed before the contained class instance to allow disambiguation for MOF models that have more than one possible containment
association between the container and the contained instance.
An example of the representation of unreferenced containment associations is
presented in Figure 6-11, where CarOwnership is an association between Family and
Car, with Car instances being contained by Family instances.
FamilyPackage “id-001? { Family “The McDonalds? { CarOwnership: Car “755-BDL? { Attribute and reference representations
} } }
Figure 6-11 An example of a containment association without references
[32] AssocInstance :=
33:
AssocBlock | 36:InfixAssocLink
[33] AssocBlock :=<AssocName>
‘{‘ 34:AssocContents ‘}’
[34] AssocContents
:= ( 35:AssocEnd 35:AssocEnd ) *
[35] AssocEnd := (<AssocEndName> (’:’ | ‘=’) )?
13:ClassInstanceRef
The third method of representing association instances involves displaying the link separately to either of the class instances
that participate. There are two forms for this: block display of the association, or infix representation of the individual
links.
In the case of block display, a list appears containing references to the class instances participating in the association.
The block consists of the name of the association followed by a block (with opening and closing braces) containing the pairs
of references to the instances participating in the relationships. Each instance in the pair may optionally be preceded by
the name of the role it plays in the association and a colon or equals symbol. Class instance references are displayed in
the style specified in
6.3, “Class Representations.? Figure 6-12 shows a block representation of an
association ‘sponsorship’ between the Family and Person classes.
FamilyPackage “id-001? { Family “The Smiths? {
Attribute and reference representations
}Person “Namdou Ndiaye? {
Attribute and reference representations
}
sponsorship {
sponsor: Family “The Smiths?
sponsored: Person “Namdou Ndiaye?
Other pairs within the sponsorship association
} }
Figure 6-12 An example of the representation for a non-containment association
[36] InfixAssocLink
:= 13:ClassInstanceRef
<AssocName>
13:ClassInstanceRef
Infix display consists of references to each of the class instances (in the form appropriate for the participating classes’
identification configuration), separated by the name of the association. It should be noted that the ends of associations
are ordered, and the participating class instances must appear in the appropriate order, with the first association end before
the association name and the second afterwards. Infix links may be optionally terminated by a semicolon. An example of infix
display is shown in
Figure 6-13, where Family is the first end of the sponsorship association, and Person is
the other end.
Family “The Smiths? sponsorship Person “Namdou Ndiaye?;
Figure 6-13 An example of infix display for associations
As mentioned in 6.5, “Reference Representations? there need only be one
representation of any an association link between a pair of class instances. This can be in the form of a reference, or using
any of the forms shown above for associations.