|Example Hardware Store|
This example is based upon a Dutch paper which is used at educational institutes to briefly introduce students into modelling methods. This paper does not contain any of the MsAccess chapters or additional cases but does show how to create SQL DDL from the initial conceptual mode.
A customer, a hardware supplier, wants to automate the stock administration. He tells the following: We have several hardware tools at stock, like hammers, saws, pliers. Up till now we administered everything on paper, but that became too much work. Every time we had to look up at which supplier we had to place an order. Needless to say this has lead to some mistakes every now and than. Ordering new hammers with Steal Ltd. Doesn't work because to only deliver pliers!
The elementary diagram below has all unique constraints and totality constraints added and shows the elementary conceptual model.
To create a database from a conceptual model is advised to group and reduce the elementary model and required to lexicalize. The diagram after this GLR is shown below and represents ER-wise the two table database.