LIS 558 - Entity-relationship diagrams in Kroenke

Kroenke* shows a version of entity-relationship diagrams that differs in some respects from the classic conventions of Chen and Jackson. Most of the correspondences are fairly obvious. One difference that may cause some difficulty is the addition of a notation for "minimum cardinality".

The point is almost always whether the minimum cardinality of an entity type in a relationship is zero or not (indicated respectively by an oval or by a crossing line). Essentially, from the minimum cardinality of one entity type in a relationship, we can predict whether occurrences of the other entity type are obligatory:

For example, Kroenke's form
says, among other things, that every course requires at least one faculty member to teach it. From this, we can predict that every course must participate in the relationship of being taught by a faculty member, which would translate into the following form in the classic scheme:

*Kroenke, D.M. 2000. Database processing: fundamentals, design & implementation, 7th ed. Chapter 3.


Home

Last updated July 5, 2001.
This page maintained by Prof. Tim Craven
E-mail (text/plain only): craven@uwo.ca
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7