a collection of one or more SAS files that are recognized by SAS software. On some hosts, the SAS data library is a single file. On most hosts, however, a SAS data library is a directory. A single SAS data library can contain an unlimited number of SAS files. Each SAS data library has two names: a physical name. The physical name of the library fully identifies the directory, file type or file mode, or host system data structure that contains the data sets. The name must conform to the rules for naming files within your host system. a logical name ( libref). The logical name enables you to provide SAS software with a single identifier for a group of data sets. See also server library.