URSAtm: a distributed system for information handling and retrieval

Abstract

The Utah Retrieval System Architecture project is an ongoing research program at the University of Utah to demonstrate a new overall system architecture for information retrieval and handling. While systems for searching large full-text or bibliographic databases have been available for well over a decade (for example, LEXIS and Westlaw for legal material), almost without exception these systems reflect the computer technology of the late 60's. They are organized around a large mainframe computer, with a number of terminals available for users. Video displays emulates hardcopy terminals, with commands being entered at the bottom of the screen and information scrolling off the top, to be lost forever. The system commands tend to be rather cryptic, especially those for altering a past query so that it can be reissued. In contrast, the URSA user interface consists of a single powerful search command, allowing the specification of a very complex search expression, coupled with a multiple-window display with an editor function present in each window. Because text can be moved freely between the windows, no special commands are necessary for modifying and reissuing a past query, saving results or queries, or including retrieved information into a new report or document. Unlike the past monolithic, mainframe-based systems, which were generally based on some key algorithm (such as a novel search or index technique), URSA is based on a small number of well-defined functions which may be implemented using a number of strategies. This architecture is well suited for a distributed envinmmont, as well as a centrnliTed processor. Information being passed to and from a module consist of of as a series of messages, using a means appropriate to the particular implementation (subroutine calls or an interprocess communications facility for a single-processor implementation, shared menm~ for a tightly-coupled nudtlprccessor version, or network communications for a loosely-conpled system). The same modules could be used in a variety of configurations, with only the underlying communications routines being changed. In the cuw~t distributed configuration, all system communications are handled by a portable, network-transparent communications system (NTCS). It is built on top of existing virtual circuit systems, such as the Apollo MBX system or TCP. The NTCS consists of a module which is bound to each application module, and has three layers: a network-dependent layer, which drives the particular virtual circuit system; a multinet layer, supporting multiple physical circulm through peer gateways; and a logical connection mMqtellarlce layer, …