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May 2005

ZTSoup: UI-Friendly Tuplebase Access

The tuplebase API is well-suited to data processing needs. But it's clumsy as the mechanism by which data in a tuplebase is to be presented and maintained in a live UI, rather than web pages or generated reports.

ZTSoup gets its name and inspiration from the Apple Newton concept. A ZTSoup is backed by the same data as a tuplebase, but that data is accessed by instantiating a ZTCrouton for each tuple that code is interested in, and a ZTSieve for the result set of any query of interest. Why the funny names? A soup has croutons floating in it, interesting ones are sieved out of it.

There are two problems with connecting a UI to a transaction-based store like the tuplebase. First, how do you efficiently identify the minimal set of interesting changes that have been made in the tuplebase. Second, in reading or writing data, what do you do when a transaction fails to commit?

ZTSoup addresses these problems by maintaining objects locally that record a snapshot of the subset of the tuplebase in which the software is interested. Local changes are recorded in those objects, and they are sent to the tuplebase as a single atomic update operation. It's simply a matter of hooking a call to the soup's Update method into the normal event loop -- all additions and removals of interest in croutons and sieves are sent to the tuplebase, and remote changes to the croutons and sieves are returned.

Because the soup may be talking to a tuplebase on the end of a comms link the update work is split into a synchronous piece, which executes in a small amount of time with no blocking, and an async piece that accumulates work done by the synchronous piece and communicates with the server as fast as latency and server CPU will allow.

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