Database Reference
In-Depth Information
make the same mistakes in the new database. Despite whatever shortcomings the current
database may have, it can still help you identify a number of the fields and tables that you
should include in the new database.
There's one rule you should keep first and foremost in your mind as you're analyzing the
current database:
Do not adopt the current database structure as the basis for the
new database structure.
Following this rule will help you avert unnecessary errors and aid in maximizing your
design efforts.
Every so often, there's a point during the analysis when a novice database developer (and
sometimes an experienced one) will stop and think, “This database doesn't look too bad.
Let's just end the analysis here and use this database as the basis for the new one.” This is
a particularly bad idea because every hidden problem within the current database structure
will be transferred into the new database. These types of problems include awkward table
structures, poorly defined relationships, and inconsistent field specifications; they will in-
variably surface later and at the least opportune times. Therefore, you should do your best
to avoid this perilous situation by following the aforementioned rule. Just remember that
it's always better to define a new database structure explicitly than to copy an existing
structure. After all, if the old database didn't have problems, you wouldn't be building a
new one.
You'll typically analyze paper-based databases and legacy databases during this part of the
design process. Many organizations use both types of databases to some degree, and you
perform the same basic analysis process on each of them. There are minor differences in
the way you analyze a paper-based database and a legacy database, to be sure, but the dif-
ferences have more to do with the databases themselves than with the overall analysis pro-
cess. You needn't be concerned with these differences, however, because I've seamlessly
incorporated them into the analysis process presented in this topic.
Paper-Based Databases
A
paper-based database
incorporatesdatathatisliterally collected, stored,andmaintained
onpaper,andyou'llfindtheseitemsinavarietyofshapes,sizes,andconfigurations.Some
of the more common formats include index cards, handwritten or printed reports, and vari-
ous types of preprinted forms. Anyone who has ever worked in an office for a business or
organization is very familiar with this type of database.
You'll find that analyzing a paper-based database can be a daunting task. One of your most
immediate problems is finding someone who completely understands how the database
works so that you can learn its use and purpose. There are several problems with the data-
