Files are objects of type *FILE that are contained in libraries. Database files contain the organized collection of data that is the lifeblood of any organi-zation. Device files allow the computer to interact with people. Because of their importance, files deserve detailed coverage.
Many types of files exist. Before you continue reading about them, it is impor-tant that you recognize the following file types:
Physical files. Physical files contain data and are subdivided into database and source physical files.
Logical files. Logical files provide alternate views to the data stored in physical files. For example, you can create a logical file that presents data in a different sequence or omits certain records. Logical files can also combine data from two or more physical files so that all the presented data appears to be stored in one physical file.
Device files. Device files are used for communications between a program and a physical device, such as a display station. The device file contains a layout of the data that is coming into or going out of the program. Device files are subdivided by device type, so there are display, printer, tape, and diskette device files. The word "device" is frequently removed in these cases. For example, display device files are referred to as display files.
Message files are not actual files; they have a different object type (*MSGF instead of *FILE). Message files are not discussed in this chapter.
Stream files are nonstructured, variable-length collections of characters and are stored in the Integrated File System. Stream files are not discussed in this chapter.