Transcript
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.
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