[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Opinions requested
David Megginson wrote: > A DBMS is something that manages data *and* passes the ACID test > (Atomicity, Consistency, Isolation and Durability). This isn't a > question of "I want feature X" -- the ACID test is what distinguishes > a DBMS from, say, the Unix file system (which can also manage data). I am going to be the old fogey here, with experience of databases going back to IMS and R: ACID is (one possible) test of a transaction processor, not of a database. It was precisely the misguided emphasis upon ACID qualities which bloated the relational model into the transaction-oriented behemoths sold today. For at least ten years we have tried to undo that direction by re-imagining the original relational concept as the data warehouse and, when that too became too bloated, the data mart. There is an opportunity with a true XML database to describe, and implement, transactions without surrendering to the siren song of two-phase commit. The key is understanding that there is no obvious or natural boundary to a transaction. Because of the inherent differences in the perspective of every participant to a transaction, each or them will describe a different set of elements to the transaction and different specific relationships among them. In the data world there is no omniscience which sees the transaction whole: to imagine it as a single, identifiably boundable unit is to deprecate the central task of each participant--to construct a transaction which is understandable to and processable by his own system. That is an ongoing implementational task, not just a conceptual one. In the real world it resolves to this: how do I get what I have to become what you need? What I have and what you need are both structures, and the two of them will incorporate some set of similar or analogous elements, which gives them the common terms on which they can define and communicate the transaction which they are attempting to execute. The definition and the maintenance of each of these structures is the role of the database. Yet each of those structures is peculiarly unique, and both are ephemeral in the specific terms of the transaction which they facilitate. Yes, the transaction, once executed, endures. But the terms in which that durability is communicated--indeed the very substance as which it is preserved--may be utterly different in the systems (and, I would hope, in the databases) of each of the participants. Precisely what each of those systems, or databases, does not exhibit are the ACID qualities through which some would hope to define the identity, uniqueness and permanence of that transaction. Respectfully, Walter Perry xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|