Until the end of March, the best bargain in database software is the $99 introductory price of Personal R:Base from Microrim of Redmond, Wash. It runs on IBM and compatible computers.

Unless you develop database applications for others or need your own applications to be available to multiple users on a network, Personal R:Base does everything that Microrim's new $795 R:Base version 3.1 does.

What's more, any application and data files that you create in Personal R:Base can be moved without modification into R:Base 3.1 if you need the latter program's extra features at some point. Beginning in April, the suggested retail price of Personal R:Base is scheduled to increase to $299.

Database software is divided into several categories, the most sophisticated of which is the true relational database, which was pioneered on personal computers by Microrim beginning in 1981. R:Base, Personal R:Base, dBase and Paradox are examples of relational databases.

The other types are flat-file databases such as Q&A and PC-File.

"Relational" merely means that information in one table of data can be related to other tables of data as long as they have at least one item of information in common. A flat-file table of data cannot be joined to another data table. In semi-relational databases, the number of tables that can be linked is limited.

A relational database is more efficient and flexible to use than a flat-file database. A good way to visualize that advantage is to think about the needs of a merchandising business.

This kind of business needs to keep track of which customers buy what items. If you tried to do that with a flat-file database, every time a customer bought something, there would have to be a new entry complete with customer name and address and the item name, description and price.

But that would require keyboarding and storing a lot of redundant data such as repetitive entries of the same customer name and address as well as repetitive entries of item names, descriptions and prices.

In a relational database, one data table would store the customer names and address, with only one entry per customer, identifying each with a unique customer number. Similarly, the merchandise list needs only one entry per item, again with a unique item number to identify each.

Then, a third data table could record sales by merely recording the date, the customer number, the item number and the quantity. Such a scheme is much more efficient both in the time required to enter the data and the hard disk space on which to store it.

As relational database programs go, Personal R:Base is both powerful and fairly easy to use, but there is a learning curve.

Pull-down menus across the top of the screen guide you to the tasks available at each juncture of designing and using an application. There are a lot of steps to navigate through and beginners may have trouble remembering which sequence of steps are required to perform what tasks. It is easier if you take the time to run through the tutorial sessions that come with the program.

However, you can just poke around among the menus, trying out various options, or you can use the on-screen help. You'll also find that the instruction manual is attractively designed, complete and logically organized.

You can start using Personal R:Base right away without learning how to design data tables or applications, which are made up mostly of related groups of tables.

The program comes with five pre-designed database applications. There is a mailing list, an appointment calendar, a home inventory, a checkbook manager and a program to store recipes complete with shopping lists.

You can study how they are constructed to get ideas for designing your own applications.

Another handy feature of Personal R:Base is that it can use dBase files directly, without translation. That means you could take a dBase file home from the office or with you on the road in your portable computer, work on it in Personal R:Base and use the same data file in your office dBase-compatible program when you return.

Personal R:Base will run on IBM and compatible computers with at least 512 kilobytes of random access memory, DOS 3.1 or higher and a hard disk with at least 6 megabytes of free storage space. You should have at least double that, however, if you plan to design very many applications of your own.

Richard O'Reilly is a Los Angeles Times staff writer. Readers' comments are welcomed, but the author cannot respond individually to letters. Write to Richard O'Reilly, Los Angeles Times, Times Mirror Square, Los Angeles, Calif. 90053.