Many components of PMDF employ table lookup oriented information. One particular type of table is used more often in PMDF than any other. Generally speaking, this sort of table is used to transform (i.e., map) an input string into an output string. Such tables, referred to as mapping tables, are usually presented as two columns, the first or left-hand column giving the possible input strings and the second or right-hand column giving the resulting output string for the input it is associated with. Most of the PMDF databases are instances of just this sort of mapping table. PMDF database files, however, do not provide wildcard lookup facilities, owing to inherent inefficiencies in having to scan the entire database for wildcard matches.

The mapping file provides PMDF with facilities for supporting multiple mapping tables. Full wildcard facilities are provided, and multi-step and iterative mapping methods can be accommodated as well. This approach is more compute-intensive than using a database, especially when the number of entries is large. However, the attendant gain in flexibility can actually serve to eliminate the need for most of the entries in an equivalent database, and this can actually result in lower overhead overall.

A complete list of the mapping table names recognized by PMDF is provided under the index entry "Mappings". You can test mapping tables with the PMDF TEST/MAPPING (OpenVMS) or pmdf test -mapping (UNIX and NT) utility. See Chapter 31 and Chapter 32 for details.