Diagramming 101

(or The Dummy’s Guide to Diagramming)

I wanted to put this together as an easy guide for students for the diagrams required for MSC 525.

Entity Relationship Diagram

Functional Decomposition Diagram

System Data Flow Diagram

Context Data Flow Diagram

 

Entity Relationship Diagram (ERD)

Purpose: To identify the entities within the system scope.

Checklist:

Example:

erd.gif (15524 bytes)

Functional Decomposition Diagram (FDD)

Purpose: To identify the major processes (functions) in the system and break them down (decompose them) all the way down to the "event" level. The FDD is a hierarchical chart that shows (in rectangular boxes) the System as a whole is the highest level, the next level identifies highest level processes, the next level identifies the next highest level processes and so forth.

Checklist:

Example:

Image39.bmp (691318 bytes)

System Data Flow Diagram

Purpose: To show the detail of the system at the event level.

The system diagram is the compilation of all the events in the FDD and their inputs, outputs, and inter-relation.

Checklist:

Example:

Context Diagram

Purpose: To identify the scope of the system. In other words, to identify the "Context" of the system to be designed.

The Context Diagram should include a process box (rounded rectangle), normally roughly in the center of the page. The inputs and outputs of the system would normally be external entities (not entities within the system being designed). Think of the Context Diagram this way: What are the inputs and outputs to my system. The lines on the diagram represent what those inputs and outputs are.

Checklist:

Example:

Notice that the system itself is fully contained in "Member Services System."