Ad/2010-08-01 Concrete Syntax for a uml action Language for Foundational uml (Alf) Second Revised Submission

8.3.5Parenthesized Expressions

A parenthesized expression is evaluated by evaluating the contained expression and results in the values of the contained expression. The use of parenthesizes only effects order of evaluation, not how the contained expression is evaluated.

The type and multiplicity of a parenthesized expression are the same as the contained expression.

8.3.6Property Access Expressions

poleValue.im

this.node

members.name

jack.house

Concrete Syntax

PropertyAccessExpression(e: PropertyAccessExpression)
= FeatureReference(e.featureReference)

FeatureReference(f: FeatureReference)
= FeatureTargetExpression(f.expression) "." NameBinding(f.nameBinding)

FeatureTargetExpression(e: Expression)
= NameTargetExpression(e)
| NonNamePrimaryExpression(e)

NameTargetExpression(e: NameExpression)
= ColonQualifiedName(e.name)

Figure 8 7 Abstract Syntax of Property Access Expressions

1. 
   Name see Subclause 7.5
   
2. 
   Expression see Subclause 8.1
   
3. 
   ColonQualifiedName see Subclause 8.2
   
4. 
   NameBinding see Subclause 8.2
   
5. 
   NonNamePrimaryExpression see Subclause 8.3.1
   

The target expression in a property access expression may not be untyped nor may its type be a primitive type or enumeration. The identified property name must denote either:

• 
  A structural feature (owned or inherited) of the type of the target expression.
  
• 
  The name of an association end of a binary association, the opposite end of which is typed by the type of the target expression.
  

For it to be legal to use the name of an association end in a property access expression, there must be exactly one binary association visible in the current scope that meets the above criterion and the given name must not also be the name of a structural feature of the type of the target expression.

If the target expression has multiplicity [1..1], then result of the collection expression will always be a single instance. This is known as a single instance property access. If the target expression has multiplicity other than [1..1], then the property access expression is known as a sequence property access. Such an expression is equivalent to a collect expression (see Subclause 8.3.21) as described below under Sequence Property Access.

The type of a property access expression is the same as the type of the named property. The multiplicity upper and lower bounds of the property access expression are equal to the product of the upper and lower bounds, respectively, of the named property and the target expression.

A property access expression is evaluated by first evaluating the target expression, which results in a sequence of instances. The result of the property access expression is then a sequence containing the union of the values of the named property for each of the target instances.

Single Instance Property Access

In the case of a single instance property access expression, the target expression will always evaluate to exactly one instance. If the property name is for a structural feature, then the resulting values of the property access expression are the values of that structural feature for the given instance.

A property access expression may also be used to access the values of an opposite association end of a binary association in which the instance participates. In this case, the resulting values are the values of named end of all links of the association for which the value of the opposite end is the given instance.

As an example of an association end access, consider the following association (represented in Alf notation—see Subclause 10.4.5).

assoc Owns {

If the association Owns is in the current scope (that is, visible without qualification), and jack is a Person, then the expression

jack.house

is equivalent to the association read expression (see Subclause 8.3.9)

Owns::house(owner => jack)

Sequence Property Access

A sequence property access expression of the form primary.name is equivalent to a collect expression (see Subclause 8.3.21) of the form

primary -> collect x (x.name)

NOTE. It is not an error for the result of the target expression in a property access expression to be empty. In this case, the property access expression evaluates to an empty sequence.