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2.3 Data dictionary (DD) 
The data dictionary (“data dictionary”, DD) contains the detailed specification of the data types which are 
exchanged within the system concerned. Each entry in the data dictionary contains an explanatory note 
relating to the particular data type and a list of elements (attributes) which are contained in the data type. 
The data dictionary contains entries relating to the data flows and memories which are represented in 
the data flow diagrams. 
Complex data flows are specified in the data dictionary by data elements. In this case elementary data 
types are involved, which cannot be broken down into further data units. In analogous manner to the 
partitioning of processes (see 2.2), therefore, data flows can likewise be broken down recursively into 
smaller units, until each data flow is described by a unique set of elementary data types.