Our most direct experience is with an object description language (Keyword/Value Notation) developed by the Consulatative Committee for Space Data Systems (CCSDS), as used for distributed file management and long-term archive products. We also have recently developed a distributed search model and distributed search system known as the Distributed Object Manager (DOM), now in use by several laboratory projects.
Here are a few excerpts about our search system...
DOM is a general-purpose distributed cataloging system. It is general- purpose by means of a schema language that provides specification of types, common attributes, object attributes and collections. A client-server architecture with an SQL-like server protocol language supports flexible distribution. It is a catalog system in the sense that it maintains meta-data descriptions of well-identified objects and supports appropriate search and description features, but it does not try to support full traditional DBMS functionality.
DOM employs a kind of hierarchical organization of collections, except that multiple parent collections are possible. This structure, known as the collection lattice, is a principal organizing mechanism which supports attribute sharing, access permissions, search paths as well as the logical integration of multiple servers.
DOM also employs a type system for classifying objects, which can be considered another organizing feature that cuts across the collection lattice. The type system serves the traditional role of providing an attribute template for sets of objects. It also serves a very important role for supporting distributed queries based on object type.
The DOM system provides a systematic scheme for organizing large numbers of servers to work effectively together. The goal is to approach the kind of uniformity and simplicity in the distribution model of the World-Wide-Web, and yet support the kind of sophisticated queries associated with database systems. The collection lattice, the type system and common attributes are the essential mechanisms for accomplishing this multi-server integration.
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