Once the MFS is complete, it can be added to any file. There are several options for installing the MFS. Each offers slightly different capabilities.

Developers can install any number of MFSs onto a file, and can mix their own MFSs with system MFSs such as SI.MFS and QUICKDEX.MFS. Some MFSs, however, are sensitive to the sequence in which they are called. For example, SI.MFS absorbs several BFS calls in their entirety, and does not pass them on to the next MFS or to the BFS.

Because of this, developers need to be aware of the effect of other MFSs that precede or follow their own MFS, and place their MFS accordingly.

Manual MFS Installation

If intended to be a permanent addition to the file, the MFS is installed by adding its name to the media map (REVMEDIA) entry for the file. A manual installation consists of updating the media map entry for a file with the MFS name, and (re)attaching the file. After the file has been attached, the MFS will be called for all access to the file. To install an MFS manually, follow the instructions listed below.

Because it requires that the REVMEDIA file be attached, the manual installation procedure can only be performed from the SYSPROG account.  However, this procedure can be performed to install an MFS onto a file that belongs to any account.

  1. Attach target media map.  Determine the volume name for the file onto which the MFS is to be installed. For example, if the file is on the default directory, the volume name is DATAVOL. Attach the media map for the volume by entering the ATTACH_TABLE command using the System Monitor.  For DATAVOL, the output is shown below:



  2. Edit media map entry for file.  Once the REVMEDIA file is attached, its records can be edited in the System Editor, just like records in other OpenInsight files. Records in the REVMEDIA file have a two-part key (filename*applicationname). The REVMEDIA record for the CUSTOMERS table in the EXAMPLES application, before installing SIMPLE_MFS, is shown below:



  3. Add MFS Name.  Field 2 of the media map entry is reserved for MFS names. If the field is empty, simply enter the name of the MFS to be associated with the file.

    If more than one MFS is associated with the file, the field uses value marks to separate the MFSs. Add the MFS name and any required value marks to field 2. Each MFS will be called in the order it appears in field 2, left to right.  Below is how the REVMEDIA record displays after adding SIMPLE_MFS to the front of the MFS chain.


     

  4. Save the record.

    Exercise care whenever editing records in the media map. Errors made in editing the map can result in map corruption, resulting in loss of access to files stored on that volume.

    When multiple MFSs are installed onto a file, the order in which they are called can be critical.   For information on position sensitivity of OpenInsight system MFSs, read the topics on MFS programming later in this chapter

  5. (Re)Attach the File.  This can be accomplished by logging out and logging back into the application containing the file, or by using the ATTACH_TABLE command from the System Monitor.
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