Links represent relationships (constraints) that exist between UOBs. There are three types of links:
•Precedence Links: Represent simple temporal precedence between the instance of one UOB and another UOB.
•Relational Links: Also called user-defined links. Highlight the existence of a user-defined relationship between two or more UOBs.
•Object Flow Links: Highlight the participation of an object in two UOB instances and also imply precedence.
Relational and object flow links are used to convey more information than simple temporal precedence between the participating UOBs. The special constraints on relational and object flow links are recorded in a link specification document. This specification document is similar to a UOB elaboration.
When you define a link, System Architect creates a link elaboration which specifies what objects are shared between the preceding and the successive UOB in the process description.