Field Specifications - Database Design for Mere Mortals - page 230

fusion and can inadvertently obscure the field's true identity and purpose. Avoid
using a description such as this:
Item Reorder Level—minimum number of items that must exist
for a particular product. (See description for Quantity On Hand.)
• Do not use examples. As you learned in Chapter 7 , using examples in a description
is a bad idea because they depend on supplemental information to convey their full
meaning. You can ensure that a description is clear and succinct by keeping it ab-
solutely free of examples.
Figure 9.4 shows the General Elements section of a Field Specifications sheet for an
E MPLOYEE ID N UMBER field.
Figure 9.4. The General Elements category for an E MPLOYEE ID N UMBER field
Physical Elements
Thiscategorypertainstothestructureofafield.Itselementsareexpressedingeneralterms
because each RDBMS program implements them in a slightly different manner. Establish-
ingtheseelements duringthisphaseofthedesignprocesshelpsyouensureconsistent field
definitions throughout the database and reduces the time it will take you to implement the
field structures in an RDBMS program.
Data Type
This element indicates the nature of the data that the field stores.
In Chapter 1 , “ Relational Databases , ” you learned that Structured Query Language, or
SQL, is the standard language used to create, modify, maintain, and query relational data-
bases. SQL is actually a fully documented standard set forth jointly by the American Na-