Context Diagram – Data Flow Diagram

What is DFD ?

Data Flow Diagramming is a means of representing a system at any level of detail with a graphic network of symbols showing data flows, data stores, data processes, and data sources/destinations.

Usually this technique starts with a very high level graphical representation showing and overall picture of the business and processes and continues down to the lower levels of the process through the presentation.

The purpose of data flow diagrams is to provide a semantic bridge between users and systems developers.

The diagrams are:

graphical, eliminating thousands of words logical representations, modeling WHAT a system does, rather than physical models showing HOW it does it hierarchical, showing systems at any level of detailJargonless ,allowing user understanding and reviewing.

Context Diagram

• defines the scope of the system by identifying the system boundary

• contains: – one process (which represents the

entire system)– all sources/sinks (external entities)– data flows linking the process to

the sources and sinks (external entities)

Some Examples ER / CONTEXT DIAGRAM / DFD

If Journals are included

How will the ER change ?

BOOK ISSUE MANAGEMENT

SYSTEM

MEMBERSHIPMANAGEMENT REPORT

MANAGEMENT

Request forMembership

Issue / Denial ofMembership

CATALOGUE SYSTEM

Supplies Book Info / Issue Details

Penalty Amount

What happens if there are constraints On the number of issues of booksIs 2nd level DFD needed ?

level 1 data flow diagram for Inventory System

level 2 data flow diagram for process 4, Reorder stock Note the numbering scheme. Processes 4.1, 4.2, 4.3, 4.4, and 4.5 are sub-processes of level 1 process 4.