You can specify disc v olume restrictions in the follo wing ways:

Use the volume name option or the volume class option of HPFOPEN or the device parameter of FOPEN to specify either a v olume name or a v olume class name. This restricts the placement of your ￿le s extents to either the speci￿ed v olume or the speci￿ed v olume class within the volume set, thus facilitating ￿le portability .

Using FOPEN , you can restrict the placemen t of a ￿le extent to a speci￿ed v olume or a speci￿ed volume class within the v olume set assigned to the group in whic h the ￿le will be created.

Using FOPEN , you can specify a v olume name or a v olume class in a w ay that main tains FOPEN compatibility with MPE V/E-based systems. F or example, MPE/iX translates a logical device number (LDEV) passed to FOPEN into the volume name currently mounted on the disc drive and places the volume name in the ￿le label.

For more information on specifying disc v olume restrictions, refer to Accessing Files Programmer's Guide (32650-90017).

File Directory Structure

File directory structure is based on sev eral ￿le characteristics that determine ho w the ￿le is classi￿ed and how it is handled during ￿le manipulation operations. These c haracteristics are discussed in the follo wing subsections.

Domains

Files can be classi￿ed on the basis of domain. The domain of a ￿le determines if it is permanent, is temporary (lasts only for the duration of the job or session), or exists only for one particular process.

The File System main tains separate directories to record the location of PERMANENT and TEMP ￿les. PERMANENT ￿les are recorded in the System File Directory; and TEMP ￿les, in the Job Temporary File Directory . A permanent or temporary ￿le can be opened or closed with a ￿le domain of OLD (although you cannot create a ￿le with an OLD domain by using the MPE/iX command :BUILD ).

This designation di￿ers from PERMANENT only in the fact that ￿rst the Job T emporary File Directory and then the System P ermanent File Directory are searc hed for the ￿lename. OLD ￿les are described in the \Closing a File" subsection. There is no File System directory for ￿les that exist only to their creating process ( NEW ￿les).

The subsections belo w de￿ne domains and describe ho w to change, list, and searc h for the domain of a ￿le and ho w to open and close ￿les with v arious domains. Table 6-1 summarizes the features of NEW, TEMP, and PERMANENT ￿les.

File System 6-5