Every SAS data set has a two-level
name of the form libref.filename.
You can always reference a file with its two-level name. However,
you can also use a one-level name (filename)
to reference a file. By default, a one-level name references a file
that uses the libref WORK for the temporary SAS library.
Note: This section separates the issues of permanent versus temporary files and one-level versus two-level names. Other topics in this documentation and in most SAS documentation assume typical use of the WORK libref, and refer to files that are referenced with a one-level name as temporary files. Files that are referenced with a two-level name are considered permanent files. ...