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Programmers must therefore rely on other means of communicating with an MFS.  One method is to use global or labelled common areas. The other is to use the contents of arguments (such as the contents of data records) to pass information to the MFS.

Global and Labeled Common Variables

Global areas available to an MFS include system @-variables (@USERNAME, @ENVIRON_SET, etc.), user-defined global variables (@USER0-4), and labelled common areas.

A security MFS, for instance, might use the user name and privilege level variables to control access to files. A more sophisticated security system can establish a labelled common area at logon time. The labelled common area might contain lists of files and fields that the user has access to, to be examined by the MFS at every file operation.

Modifying MFS Arguments

The arguments for filing system calls come from the various elements of BASIC+ statements. A programmer can thus pass information or keys to the MFS by simply passing them along with data.

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