We again consider the book data management problem that was considered in Part 1. But now we also consider the data integrity rules (or 'business rules') that govern the management of book data. These integrity rules, or constraints, can be expressed in a UML class diagram as shown in Figure 4.2 below.
In this model, the following constraints have been expressed:
Due to the fact that the
isbnattribute is declared to be the standard identifier ofBook, it is mandatory and unique.The
isbnattribute has a pattern constraint requiring its values to match the ISBN-10 format that admits only 10-digit strings or 9-digit strings followed by "X".The
titleattribute is mandatory, as indicated by its multiplicity expression [1], and has a string length constraint requiring its values to have at most 50 characters.The
yearattribute is mandatory and has an interval constraint, however, of a special form since the maximum is not fixed, but provided by the calendar functionnextYear(), which we implement as a utility function.
Notice that the edition attribute is not mandatory, but
optional, as indicated by its
multiplicity expression [0..1]. In addition to the constraints described
in this list, there are the implicit range constraints defined by
assigning the datatype NonEmptyString as range to
isbn and title, Integer to
year, and PositiveInteger to
edition. In our plain JavaScript approach, all these property
constraints are coded in the model class within property-specific
check functions.
The meaning of the design model can be illustrated by a sample data population respecting all constraints:
Table 4.1. Sample data for Book
| ISBN | Title | Year | Edition |
|---|---|---|---|
| 006251587X | Weaving the Web | 2000 | 3 |
| 0465026567 | Gödel, Escher, Bach | 1999 | 2 |
| 0465030793 | I Am A Strange Loop | 2008 |