Conclusion

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That's it. We now have a plan for the implementation of each of our eight rules for our sample horse racing application. Table 4-1 lists our decisions. Notice that only two of the eight rules will be implemented in business objects. The remaining six will reside in the database as foreign key, unique, and check constraints, and in one case as an identity column. We won't, however, stick with the identity column solution for very long. We'll swap it for a Visual Basic solution, lowering the SQL total to five rules out of eight. Only three will be implemented as MTS or COM+ components in the business services tier of our sample.

Table 4-1. Rules and their implementation.

Rule #	Rule	Implementation
1	Bred in country.	Database: foreign key
2	One and only one trainer.	Database: foreign key
3	Value of sex must be valid.	Database: check constraint
4	Only one kind of sex change allowed.	Business object: Visual Basic
5	Between 1 and 15 years old.	Database: check constraint
6	Don't delete a horse that has run at least one race.	Business object: Visual Basic
7	Unique combination of name and country where bred.	Database: unique constraint
8	Unique ID when inserted.	Database: identity column (for now)