In its simplest form, a data file uses fields of the same length for each item of data, for example, a plain EBCDIC or ASCII file would look like:
MN573 T-shirt Green 18.95
AY621 Blouse Blue 22.95
A common format stemming from the BASIC programming language is an ASCII comma separated values (CSV) file. The data above would look like this:
MN573,T-shirt,Green,18.95
AY621,Blouse,Blue,22.95
"MN573","T-shirt","Green","18.95"
"AY621","Blouse","Blue","22.95"
Both formats above are simple, contain only data (except for quotes and commas) and can be easily manipulated by a word processor. However, other types of data files may also contain special codes that identify the way the data are structured within the file. For example, variable length records require a code in each field indicating the size of the field.
Whether fixed or variable length fields, the data in non-DBMS systems is linked directly to the processing. The program must know the layout of the fields in each record, and it cannot accept records in a different format. In order to process a different file format, the program must be changed.
Incompatible file formats often exist within the same organization because they were developed separately. For example, one record may reserve 40 characters for name, while another holds only 30. As long as a file management system is used rather than a database management system (DBMS), the program that processes the first file structure would have to be changed to process the second. See
standards.