Terminology - Database Design for Mere Mortals - page 39

Figure 3.8. An example of a validation table
I'll discuss validation tables in more detail in Chapter 11 , “ Business Rules . ”
Field
A field (known as an attribute in relational database theory) is the smallest structure in the
database and it represents a characteristic of the subject of the table to which it belongs.
Fields are the structures that actually store data. The data in these fields can then be re-
trievedandpresentedasinformationinalmostanyconfigurationthatyoucanimagine.The
quality of the information you get from your data is in direct proportion to the amount of
time you've dedicated to ensuring the structural integrity and data integrity of the fields
themselves. There is just no way to underestimate the importance of fields.
Every field in a properly designed database contains one and only one value, and its name
will identify the type of value it holds. This makes entering data into a field very intuitive.
If you see fields with names such as F IRST N AME , L AST N AME , C ITY , S TATE , and Z IP C ODE ,
you know exactly what type of values go into each field. You'll also find it very easy to
sort the data by state or look for everyone whose last name is “Hernandez.”
You'll typically encounter three other types of fields in an improperly or poorly designed
database:
1. A multipart field (also known as a composite field), which contains two or more
distinct items within its value
2. A multivalued field, which contains multiple instances of the same type of value
3. And a calculated field, which contains a concatenated text value or the result of a
mathematical expression
Figure 3.9 shows a table with an example of each of these types of fields.