Information Management System: Master links — a hierarchical data system

MASTER LINKS is a software system used to build, administer, and access hierarchical data bases. It is designed to operate in a time-sharing environment, and, in particular, it allows multiple concurrent updates and retrievals on the same data base. A BUILD module is used to specify the hierarchical configuration of a data base and an initial “storage mapping” of the elements of the hierarchy into a particular file layout. A set of administrative routines is provided for altering the mapping and other such maintenance purposes. The access routines have three levels of interface, from primitive and flexible to sophisticated and functional. The interfaces are all defined in terms of the hierarchical structure and independent of the storage mapping. Thus, an alteration of the storage mapping for a data base does not require changing any programs that access data using these interfaces. The lowest-level interface enables the calling program to add to the data base, update a value, or retrieve a value, in terms of a hierarchy position. The second-level interface facilitates traversal of a hierarchy by enabling the calling program to specify portions of the hierarchy over which a process is to operate. Such a specification, called an “access tree,” consists of data which can be generated at execution time by the calling routine. As in the first level, data are transferred one at a time. The third-level interface is a function evaluation mechanism which computes values from data base values and other computed values according to function definitions passed to it at execution time. Like an access tree, a function definition is itself data which can be constructed at execution time by the client process.