What is the Xanadu Hypertext System?

The Xanadu Hypertext System is a tool for storing, retrieving, and organizing information, although it is not a "database management system" in the traditional sense of the term. It differs both in its form and its function.

In the Xanadu System, information is stored in the form of documents: letters, memos, articles, engineering specifications, scribbled notes, textbooks, manuals, computer programs, contracts, reports, and so on. These can vary greatly in their size and in the nature and complexity of their internal structure. This contrasts sharply with database management systems, where the information stored consists of aggregates of records holding chunks of data in fairly fixed formats and in fairly homogeneous arrays. In short, DBMS's store lists of items, where every item in the list has the same structure. Clearly, these two forms of information storage have different purposes and are appropriate for different kinds of information.

DBMS's arose out of traditional record keeping systems in which information was stored on paper in the form of ledgers, lists, card files, etc., and the storage, retrieval and update functions were performed by hand, often by armies of clerks. As these functions were computerized, it was discovered that the computer made possible a variety of capabilities that had not previously been considered. In addition to allowing vastly larger bodies of data to be accessed and manipulated far faster and more accurately than ever before, entirely new functions could be performed. It was found that if the data was stored according to certain kinds of generalized schemes, one could impose different patterns of organization on the same body of data, allowing appropriately different organization schemes to be used for different applications. Also, it was realized that one could store information about the relationships between different chunks of data, in addition to storing the data itself, and then manipulate this relational information as well, using the very same techniques. One could even store relational information about other relational information, ena-bling the most general organizational structures to be built.

Today, DBMS's are a standard tool for handling information. Research goes on to make them ever more powerful, efficient, and general-purpose. Tomorrow's DBMS's will be even more sophisticated.

Techniques for handling information in the form of documents, however, have not kept pace with database technology. While there are numerous systems available which allow one to store, retrieve, and to some extent manipulate document type data using a computer, systems that allow one to organize and interrelate this information, in the sense that DBMS's allow one to organize and interrelate bulk data, have been crude to non-existent. The Xanadu Hypertext Systems ends this state of affairs.

The Xanadu Hypertext System is the first and so far the only effective system for document management which allows one to organize and interrelate document type information in a totally general and application independent fashion.

This is what the Xanadu Hypertext System can do:

--It can store, retrieve, and update documents on command.

--On command, it can create explicit linkages between arbitrary sets of arbitrary portions of arbitrary documents and other linkages. It can retrieve these linkages at will, including information about what is being linked to what and about the nature and type of the link itself. It can correctly maintain these linkages in the midst of changes to the very data being interlinked.

--It can maintain multiple versions of any given document, efficiently storing the common portions in common, with separate portions of storage required only for those parts of the documents which are actually different. It can provide historical traceback information in dated chronological order about any and all changes to a given document, for purposes of error recovery or auditing.

--It can do all of this efficiently, with logarithmic overhead in terms of both storage space and response time. This means that storage requirements will grow as a constant multiple of the volume of data stored (as opposed to many systems of various sorts in which storage overhead increases much faster than the volume of data does). Response time will remain effectively constant no matter how vast the body of stored documents may become. It can make effective use of ultra-high density write-once storage technology, such as video disks. It can effectively and efficiently operate in a totally distributed storage environment in which the data is spread over a network of intercommunicating computers which may be located all over the country or all over the world.

That is what the Xanadu Hypertext System can do. No other system is available that can do these things. Quite probably none will be for some time to come.