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Base creates

relational databases

. This makes it fairly easy to create a

database in which the fields of the database have relationships with

each other.

For example: Consider a database for a library. It will contain a field

for the names of the authors and another field for the names of the

books. There is an obvious relationship between the authors and the

books they have written. The library may contain more than one book

by the same author. This is what is known as a one-to-many

relationship: one author and more than one book. Most if not all the

relationships in such a database are one-to-many relationships.

Consider an employment database for the same library. One of the

fields contains the names of the employees while others contain the

social security numbers, and other personal data. The relationship

between the names and social security numbers is one-to-one: only one

social security number for each name.

If you are acquainted with mathematical sets, a relational database can

easily be explained in terms of sets: elements, subsets, unions, and

intersections. The fields of a database are the elements. The tables are

subsets. Relationships are defined in terms of unions and intersections

of the subsets (tables).

To explain how to use a database, we will create one for automobile

expenses. In the process, we will be explaining how a database work.

Planning a database

The first step in creating a database is to ask yourself many questions.

Write them down, and leave some space between the questions to later

write the answers. At least some of the answers should seem obvious

after you take some time to think.

You may have to go through this process a few times before everything

becomes clear in your mind and on paper. Using a text document for

these questions and answers makes it easier to move the questions

around, add additional questions, or change the answers.

Here are some of the questions and answers I developed before I

created a database for automobile expenses. I had an idea of what I

wanted before I started, but as I began asking questions and listing the

answers, I discovered that I needed additional tables and fields.

What are the fields going to be? My expenses divided into three broad

areas: fuel purchases, maintenance, and vacations. The annual cost for

Chapter 8 Getting Started with Base 239

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OpenOffice.org OpenOffice - 3.0 Quick Start Guide Page 239