For those who may be unfamiliar with databases, think of a filing cabinet filled with folders of invoices ordered alphabetically by company name. If we wish to transfer this information into our computer database we have two choices for data file I/O: a simple sequential file or a random access file.

Sequential Access Data Files

The concept of using a sequential file to store invoice data by company name is very simple. Just enter the data as it is found in the filing cabinet. To access the information, begin reading at the start of the file and continue until finished.

With this method, the time required to find a specific record greatly increases as more and more records are added to the data file. Also, the act of adding information while trying to keep the file in alphabetical order becomes very time consuming since many existing records will have to be moved in order to make room for the new record.

Random Access Data Files

Random access techniques allow easier access to any particular data record. To find a data record, all that is required is the desired record number. You can then seek to the proper location within the data file and retrieve the desired record.

But how does the program know which record number to use? And what about adding records in the middle of the data file? How can the program update or append records to the database file and still maintain a particular record order? These problems are easily solved by the use of a Database Management System (DBMS) such as xBase.