How To Read A Data Model
Understanding a Data Model Helps in Understanding Requirements and Application Design
Issue: 7.3 (March/April 2009)
Author: Craig Boyd
Article Description: No description available.
Article Length (in bytes): 23,806
Starting Page Number: 22
RBD Number: 7310
7310 graphics.zip Updated: Monday, March 2, 2009 at 1:37 PM
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Excerpt of article text...
In this article I intend to explain to you what a data model is and how to read one.
Within the field of data modeling there are several kinds of models and in order to make sure we are all talking about the same thing I need to briefly lay out, in general terms, the kinds of Information Models that exist. For the purpose of this article I will use a fictitious movie rental company, called "Movies R Us".
For the sake of clarity let me define a few terms. An entity at a high level represents a general concept, but as we move further down into lower level models it will become a more concrete or discrete concept. For example, a high level entity might be "Product" and then a little lower it may become a couple different entities like "Movie" and "Consumable Product."
At a high level there is the Entity Relationship Diagram (ERD). Many times an ERD is confused with other types of lower level data models. But an ERD is really designed to show the major entities and the relationships between those entities. So in our example of a DVD rental company we might have entities like "Movie", "Customer", "Rental", "Transaction", and "Account". Included would be the relationships between these various entities. A Customer can have either zero or one Account. An Account can have zero, one or more Rentals associated with it. A Customer initiates a Transaction to rent/buy a Movie for their Account. Note that you will not see any attributes or characteristics of the entities at this level.
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