Programming the Perl DBI

Flat-File Databases

The simplest type of database that we can create and manipulate is the old standby, the flat-file database. This database is essentially a file, or group of files, that contains data in a known and standard format that a program scans for the requested information. Modifications to the data are usually done by updating an in-memory copy of the data held in the file, or files, then writing the entire set of data back out to disk. Flat-file databases are typically ASCII text files containing one record of information per line. The line termination serves as the record delimiter.

In this section we’ll be examining the two main types of flat-file database: files that separate fields with a delimiter character, and files that allocate a fixed length to each field. We’ll discuss the pros and cons of each type of data file and give you some example code for manipulating them.

The most common format used for flat-file databases is probably the delimited file in which each field is separated by a delimiting character. And possibly the most common of these delimited formats is the comma-separated values (CSV) file, in which fields are separated from one another by commas. This format is understood by many common programs, such as Microsoft Access and spreadsheet programs. As such, it is an excellent base-level and portable format useful for sharing data between applications.^[8]

Other popular delimiting characters are the colon ( : ), the tab, and the pipe symbol ( |