How are unqualified identifiers looked up in an index?
First of all, it is important to know that when indexing, all identifiers are assigned to a specific name space, with unqualified or uncontrolled identifiers in the UCID class being assigned to an ad hoc user name space. The xdformat and xdget programs maintain an internal priority list of the possible name spaces. When provided with an unqualified identifier, xdget works its way down the priority list, successively looking for the requested identifier in each name space. The program stops at the name space in which the first matching identifier is found; any further work the program must do (e.g., to identify the earliest appearance of the identifier in the database) will be performed in this one name space. Name spaces are examined in the decreasing priority order shown in Table 3. The qualifiers 1 and 2 on any given tag correspond respectively to the 1st and 2nd fields in the tags full identifier syntax. Note that non-standard accession tag may be used with the T option as a synonym
