DFD= data flow diagram. Data flow diagram (DFD) is a main tool that can comprehensively describe the logical model of information system. It can fully reflect the flow, processing and storage of information in the system with fewer symbols. DFD consists of four elements: data flow, processing, data storage and external entities. External entities refer to individuals or organizations that exist outside the software system. It points out the source of data needed by the system and the destination of data generated by the system. /view/275854.htm

DD (Data Dictionary) is a directory that users can access to record database and application metadata. Active data dictionary refers to a data dictionary whose contents can be automatically updated by DBMS when the structure of database or application is modified. A passive data dictionary refers to a data dictionary whose contents must be updated manually when it is modified. /view/2 1965 . htm # sub 5064794