Bending or Breaking the Rules - Database Design for Mere Mortals - page 415

15. Bending or Breaking the Rules
Nature never breaks her own laws.
—L EONARDO DA V INCI
Topics Covered in This Chapter
When May You Bend or Break the Rules?
Documenting Your Actions
Summary
I always advocate following proper database design techniques. As you've already learned,
there are numerous reasons for doing so. But first and foremost, you should use a good
design method to ensure the integrity of the database. I cannot overstate how important this
is. You now know the consequences of improperly establishing data integrity, so following
the rules is of paramount importance.
When May You Bend or Break the Rules?
There are only two specific circumstances under which it is at all permissible to bend or
break the rules of proper database design. Unless either of these is an inescapable imperat-
ive, you should use proper database design techniques when designing your database.
Designing an Analytical Database
As you learned in Chapter 1 , “ Relational Databases ,” an analytical database stores and
tracks historical and time-dependent data. This type of database often contains calculated
fields within some of its table structures. The expressions used in many of these fields are
meant to record the state of a particular set of data at a given moment in time; other fields
store the results of aggregate functions.
Youmayhavealreadysurmisedfromthedescriptionthatthistypeofdatabaseviolatesprop-
er database design because its tables contain calculated fields (refer to Chapter 7 , “ Estab-
lishing Table Structures ”). In this particular instance, the violation is acceptable because of
the manner in which the data in the database is being used. I recommend that you properly
design the database first and then break the rules only after judicious consideration—you
should make a deliberate decision to break a rule and understand why doing so is necessary
in the specific instance.