DSDs are a graphical alternative to the composition specifications in data definitions. A DSD shows the decomposition of data items into lower-level items. If the DSD contains only a data item and its decomposition then it is a graphical substitute for the data definition of the data item. If the DSD also shows the decomposition of the lower-level data items into further data items, it is a graphical substitute for a set of data definition composition specifications.
DSDs are not normally used instead of data definition composition specifications. DSDs offer a picture of the structure of a system’s data items, as a supplement to the DD. Even when DSDs are used, the DD is still to be regarded as the master source of information for a system’s data and control definitions.
DSDs show the composition of a data definition as the data items below it. The DSD notation corresponds, in effect, to a graphical version of the DD composition specification BNF.
DSDs are not hierarchical.
DSDs can appear in models in the Essential and Implementation Domains.
Any form of number can be used for DSDs.
An example DSD is:
The symbols available in DSDs are: