HP OpenVMS Systems

Concealed rooted logical names? (rooted directorie

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The Question is:

 
What is a rooted directory, how do you create one, and when should you use
one.
 
    ie... "sys$common"
 

The Answer is :

 
  Concealed rooted logical names are used to mask potential (or actual)
  differences in the initial component part(s) of the full file
  specification.
 
  An example of a traditional physical file name specification and an
  equivilent replacement (where DKA100: is assumed to be the local OpenVMS
  system disk) using a logical name follows:
 
    DKA100:[SYS0.SYSCOMMON.SYSEXE]
    SYS$SYSDEVICE:[SYS0.SYSCOMMON.SYSEXE]
 
  When correctly created, a concealed rooted logical name is largely
  indistinguishable from a physical device name when parsing the file.
  Unlike a more common logical name that solely references a physical
  device, a concealed rooted logical name also references (and conceals)
  a root; a directory path.
 
  An example of a concealed rooted logical name follows:
 
    DKA100:[SYS0.SYSCOMMON.SYSEXE]
    SYS$COMMON:[SYSEXE]
 
  In this case, SYS$COMMON translates to DKA100:[SYS0.SYSCOMMON.] -- the
  trailing period in the directory is significant, and required syntax.
  The SYS$COMMON logical name and any other concealed rooted logical name
  is marked with /TRANSLATION=CONCEALED.  The default logical name
  translation scheme will translate back to the physical device name,
  to the limit of translations (LNM$C_MAXDEPTH), or until it encounters
  a logical name marked as concealed.
 
  As an example of when a concealed rooted logical name might be of
  interest, consider a case where multiple group of OpenVMS users have
  a scratch disk and wish to share scratch space, but they do not wish
  to see the scratch space of other groups.  Through the use of a
  concealed rooted logical name, each of these groups can all share
  the same physical disk, but each will have the appeance of an entirely
  private disk:
 
    $ DEFINE/TRANSLATION=CONCEALED/TABLE=LNM$SYSTEM/EXECUTIVE -
        USER_SCRATCH DISK$SCRATCH:[GROUP_1.]
 
  As another example, consider a site that is upgrading from the usual
  herd of smaller disk drives into a fewer larger disks or into a RAID
  configuration.  Various applications were designed so that they each
  assumed the use of a whole disk, or potentially various versions of
  the application are now in use in parallel, and problems with the
  directory names used are encountered -- top-level directory names are
  no longer unique, and the applications are now colliding.  With the
  use of concealed rooted logical names, each application can be moved to
  a subdirectory lower down in the directory structure, but the application
  can still operate unaware; as if it were still working with top-level
  directories.
 
  There are various other uses.

  

     

     
answer written or last revised on ( 19-APR-1999 )
     
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