CPSC 333: Entity Relationship Diagrams: Introduction

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This material was covered during lectures on January 15, 1997.

• Use
• References
• More About Use

Use

Entity-relationship diagrams are used during requirements as part of structured development in order to model requirements needed to design the layouts of relational data bases or text files - that is, to describe most of the data that must be stored by the system in order for it to function correctly. More recently, these been extended or modified in order to produce (different) models that are useful for object-oriented development, as well. However, we'll begin by discussing their use in structured development.

References

My primary reference for this material is the reserve book,

Sally Shlaer and Stephen J. Mellor
Object-Oriented Systems Analysis: Modeling the World in Data

Another book with some useful information about this topic (and how it relates to some other analysis topics to be covered later) is also available on reserve:

Edward Yourdon
Modern Structured Analysis

Finally, there is also some information in the recommended course reference:

Michael J. Pont
Software Engineering with C++ and CASE Tools
Chapter 21, pages 500-517

Note, though, that Pont's book is not my primary reference for this material - and that there are some (relatively minor) differences in the notation for ERDs that I am introducing and the notation used in this text. Unless you are explicitly asked to do otherwise, you should use the notation used in the lectures instead of the notation introduced by Pont, when doing course work for CPSC 333.

More About Use

As mentioned above, these diagrams model the information that must be remembered and therefore stored by the software system over a nontrivial - and, frequently, arbitrarily long - period of time, because the information is received as input from a user or created as a system's response to a user's request at one time, and must be accessed, modified, or reported in order to deal with additional, later, requests from users.

These are not used to model any of the following:

• additional data that a system might need to read, create, or report in order to deal with a single event but that it doesn't need to remember;
• anything else (in particular, algorithms or processes that the system is required to follow).

Note: Some ``extended'' ERDs do include some of this information - this is especially true of the extended ERDs used for ``object oriented analysis'' - but the ERDs discussed in CPSC 333 will not include this. We'll use different tools to model this extra information instead.

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