Communications structure modelling is performed via Communicating Objects (CO) diagrams.
  In the previous versions such diagrams were called as CD diagrams.
  CO diagrams describe the static structure of a model and are used to represent both the division of objects into smaller subobjects and the communication between them.
The diagram may contain the following elements :
Object Represents an independently acting part of an enterprise which can communicate with other such parts. An object may be refined further via another CO diagram or represented as a process described by a PD diagram.
Internal Communication Path Links two objects and signifies that messages are transmitted from one object to another in the specified direction.
External Communication Path Represents a communication path which is continued in the CO diagram on a higher level.
Database Represents a persistent data store whose structure is described by an entity-relationship model.
Internal Access Path Connects object to a database. The following access paths are available:
  • IN (object can only read data from the database)
  • OUT (object only adds data to the database)
  • INOUT (both types of access are permitted)