Computer Programming Concepts and Visual Basic David I. Schneider

348 Computer Programming Concepts and Visual Basic
’Close the recordset referring to TABLE1
MyRec.Close
’Open a recordset referring to TABLE2
Set MyRec = T2.OpenRecordset
’Create a record
MyRec.AddNewMyRec(“FIELD2A”) = “alpha”
MyRec(“FIELD2B”) = 2000
MyRec(“FIELD2C”) = 1
’Update the recordset
MyRec.Update
’Close the recordset
MyRec.Close
’Close the database
MyDB.Close
■ PRINCIPLES OF DATABASE DESIGN
In order to design a database, you must decide how many tables to use, what fields to include
in each table, what fields to make primary or foreign keys, and what validation criteria to
specify. The programming paradigm “Plan first, code later” also applies to databases. Before
you design a database, you first must understand how the database will be used. For instance,
you must know in what way and how often the user will update the data, and what types of reports
the user will want to be generated from the database. Failure to plan ahead can be very
costly.
You have no doubt read about the “year 2000 crisis.” Databases designed in the 1960s
and 1970s saved space by using just two digits to refer to each year. As a result, they cannot
distinguish between the year 2000 and the year 1900. Correcting this oversight is predicted
to cost government and industry billions of dollars.
Good relational database design is more an art than a science. However, there are certain
fundamental guidelines that the designer should keep in mind.
Include the necessary data.
After you have a clear picture of the types of reports the user must generate, you will
know what fields and relationships to include. On the other hand, some data that seem relevant
do not have to be kept.
Be aware that data should often be stored in their smallest parts.
For instance, city, state, and zip code are usually best stored in three fields. So doing will
allow you to sort a mailing by zip code or target a mailing to the residents of a specific city.
Avoid redundancy.
The process of avoiding redundancy by splitting a table into two or more related tables
is called data normalization. For instance, the excessive duplication in Table 11.5(a) can be
avoided by replacing the table with the two related tables, Tables 11.5(b) and 11.5(c).
TABLE 11.5(A)
A Table with Redundant Data
course section name time credits prerequisite
CS102 1001 Intro to Databases MWF 8–9 3 CS101
CS102 1002 Intro to Databases MWF 1–2 3 CS101
CS102 1003 Intro to Databases MWF 2–3 3 CS101
CS102 1004 Intro to Databases MWF 3–4 3 CS101
CS105 1001 Visual Basic MWF 1–2 4 CS200