It commonly happens that a user wants to select a sub-set of the database for further searching to save on searching time. The recommended method is to make a file of the reference codes for those entries of interest, which is usually given the name with suffix .gcd, and can be presented to the QUEST program as if it were the sub-set of the database, hence the term 'virtual database' is often used. There are two great advantages of virtual databases:
Note that virtual databases are not available with the Machine Independent Package.
A reference code file may be prepared by:
The commands for starting your search on the virtual database of reference codes in file subset.gcd are as follows:
quest probname -v subset.gcd
$ ASSIGN SUBSET.GCD CSDVIRTDB $ QUEST PROBNAME TT:
Note that when QUEST starts up there will be a message that you are searching a subset, and the file name will be given.
To revert to searching the main database you need to deactivate the pointer to the sub-set, by typing:
$ DEASSIGN CSDVIRTDB