Locating Databank Files
The system databank SYSDB is always stored in a file located in the directory defined as the home directory for the database, see The Local Database. The file locations of all the other system databanks and the user databanks are stored in the data dictionary.
The file specification for the databank file is exactly as specified when the databank was created. If a databank file specification is given in full, it is unambiguously specified and no variable factors are involved in resolving the location of the file.
If a databank file specification appears in the data dictionary without an absolute directory name, the database home directory will be used to complete the file specification.
This substitution is applied whenever the location of the databank file must be determined, (i.e. when the databank is created or altered and whenever tables stored in it are accessed).
Subsequent redefinition of the database home directory or any variables used in the file specification will, therefore, alter the expected location of such databank files.
UNIX: Databases on UNIX platforms may be set up with a directory search path instead of a single home directory, see The Local Database.
VMS: Whenever a databank file is specified without a directory name under VMS, it must be located in the database home directory.
If a logical name is included in the file specification, this will be recorded in the data dictionary and will be used whenever the location of the databank file is resolved.
The flexibility achieved by not using full databank file specifications must be weighed against the loss of explicitly specified information from the data dictionary. In addition, the centralized use of mechanisms such as environmental variables or logical names in a complex system requires careful and disciplined management.
In particular, it is necessary for the database server process to have access to all relevant environmental variables and logical names in order to use them when accessing the databanks.
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