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.
Numbering of DSDsAny form of number can be used for DSDs.
SymbolsAn example DSD is:
The symbols available in DSDs are:
| Symbol | Name | Description | Definition | Expansion |
|---|---|---|---|---|
 | Comment | Makes a note anywhere in the diagram. Are always surrounded by * characters. Note: If you do not want Cradle to automatically add an * go to the Graphics Settings section of Project Setup and turn off the Automatically add asterisks to diagram's comment symbols option. | None | None |
 | Boundary Point | A connection point for the initial transition to enter the initial state. | None | None |
 | Data Object | An item of data in the system’s DD. | Data object data definition | None |
 | Selection Data Object | An item of data that appears as an optional (selected) component of another, higher level data item. It appears in the composition specification of the higher level data item within a {…|…} construction. | Data object data definition | None |
 | Iteration Data Object | An item of data that appears as an iterative (repeated) component of another, higher level, data item. It appears in the composition specification of the higher level data item within a (…) or n {…} m construction. | Data object data definition | None |
 | Picture | Allows you to choose the location of a GIF or JPEG image to be displayed as a diagram symbol or to be embedded in an existing diagram symbol. | None | None |
 | Connection | The means of interconnecting data items. | None | None |
 | Item | Represents a requirement or system note in the diagram. | None | None |
 | Context Item | Represents a requirement or system note in a diagram and is a container within which other object symbols can be drawn or attached. | None | None |
 | Cross Reference Link | Represents a cross reference that exists between a pair of system notes/requirements. It can also represent a cross reference between a system note/requirement and a specification or data definition or system that describes the objects symbols that it connects. | None | None |
