The
Role Tool
is used to specify the components that lie at
the end of a relationship connected to an object. For example, in Data Flow
Diagrams we can identify two role types: From and To, or for an Inheritance
relationship type in an object-oriented method there could be Superclass and
Subclass role types.
Roles can have properties of their own, and also symbols.
For example, in an Entity-Relationship-Attribute Diagram the roles associated
with a relationship between two or more entities have a property called
Cardinality
. In a Data Flow Diagram, the role To has a
symbol as well: the solid line with an arrow head — note that Role symbols
also specify the width and colour of the line from the object to the
relationship. If no symbol is defined, a simple 1-pixel black line is
used.
Figure 1-7. Role Tool.