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Database Design

 

Since the original version of Microcosm was a single user application, the linkbase architecture was just a single-user flat table. With the introduction of CSCW mechanisms, the need for a multi-user link database with some kind of locking mechanism was fundamental. After some research into the various possibilities of implementation [12], and available database packages, we decide to use Exodus [13] to create an object oriented multi-user linkbase. The Exodus Storage Manager is a multi-user object storage system supporting versions, indexes, single site transactions, concurrency control and recovery. It has a client server architecture where application programs (clients) may reside on a machine different from the machine or machines on which the storage manager server or servers run. For a hypermedia system such as Microcosm, we can identify the following entities:

In Microcosm, as said previously, the information about links is not embedded in the documents and resides in the linkbase. To map these Microcosm concepts onto an object oriented database, we created the following classes:

We can therefore summarize the object oriented model of the database by saying that a node is a class of objects that has a collection of source anchors and a collection of destination anchors. An anchor is a hierarchy of classes that has in common a collection of links. Each subclass of the anchor class has its particularities and new subclasses can easily be created to accommodate new types of anchors and new media. Finally, a link is a class that connects two documents. For more details see [15].



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Next: The client server architecture Up: Cooperative Microcosm Previous: Cooperative Microcosm



Fri Dec 8 14:41:14 GMT 1995