Figure 8.20 – Event class diagram

The Event element inherits the attributes and model associations of FlowElement (see Table 8.44), but adds no additional attributes or model associations.

The details for the types of Events (Start, Intermediate, and End) are defined in “Event Definitions” on page 258.

8.4.6Expressions

The Expression class is used to specify an Expression using natural-language text. These Expressions are not executable. The natural language text is captured using the documentation attribute, inherited from BaseElement.

Expression inherits the attributes and model associations of BaseElement (see Table 8.5), but adds no additional attributes or model associations.

Expressions are used in many places within BPMN to extract information from the different elements, normally data elements. The most common usage is when modeling decisions, where conditional Expressions are used to direct the flow along specific paths based on some criteria.

BPMN supports underspecified Expressions, where the logic is captured as natural-language descriptive text. It also supports formal Expressions, where the logic is captured in an executable form using a specified Expression language.

Figure 8.21 – Expression class diagram

Expression

The Expression class is used to specify an Expression using natural-language text. These Expressions are not executable and are considered underspecified.

The definition of an Expression can be done in two ways: it can be contained where it is used, or it can be defined at the Process level and then referenced where it is used.

The Expression element inherits the attributes and model associations of BaseElement (see Table 8.5), but does not have any additional attributes or model associations.

Formal Expression

The FormalExpression class is used to specify an executable Expression using a specified Expression language. A natural-language description of the Expression can also be specified, in addition to the formal specification.

The default Expression language for all Expressions is specified in the Definitions element, using the expressionLanguage attribute. It can also be overridden on each individual FormalExpression using the same attribute.

The FormalExpression element inherits the attributes and model associations of BaseElement (see Table 8.5), through the Expression element. Table 8.43 presents the additional attributes and model associations of the

FormalExpression.