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Re: Quote from comp.object

From: Anne & Lynn Wheeler <lynn_at_garlic.com>
Date: Thu, 01 Mar 2007 17:37:44 -0700
Message-ID: <m3fy8o8opz.fsf@garlic.com>

Sampo Syreeni <decoy_at_iki.fi> writes:
> In the end such an organization would probably be faster than an IMS
> database because every overhead that could be cut would have been,
> yet higher level operations like multitable joins which allow for
> cost amortization would have been properly declared in relational
> syntax, and fully exploited. Such savings are not possible under the
> interface offered by IMS, evenwhile they're the lifeblood of the RM.

as i've mentioned before ... the exchange between the IMS group and the System/R group in the late 70s ... basically was that System/R had drastically increased system overhead while significantly reducing manual/human maintenance effort.

The trade-off was that IMS carried direct pointers as part of the database "data" ... were exposed to the database applications and had to be managed and dealt with. The relational System/R implementation had abstraction that did away with the exposed record pointers and therefor eliminated significant amount of human/manual/administrative effort dealing with the exposed record pointers. The System/R "costs" were an index implemented under the covers (below the abstraction interface) that significantly drove up the number of disk I/O operations needed to reach the desired information and also typically doubled the amount of physical disk space (for typical target applications of the period) ... but eliminated the manual costs of dealing with exposed record pointers.

The change over in the 80s was general increase in people costs (driving up the human/manual/admistrative costs) and general decrease in computing hardware and resource costs ... changing human/hardware cost tradeoff decisions.

There was also significant increase in amount real storage for typical configurations ... allowing much of the relational implementation index structure to be cached, mitigating the number of actual physical disk I/Os involved in dealing with the index structure, and significant reduction in disk space cost/bit muted the issue about doubling physical disk space.

The next human constraint/bottleneck appears to be the intellectual effort related to "normalization". Some past studies have indicated that this is significant enuf that some large organizations were found with six thousand different RDBMS deployments ... where over 90precent of the information was common. The evoluation appears to have been that a RDBMS (potentially because of the normalization contraints) is relatively specific mission oriented (potentially a number of different applications, but still focused on a specific business mission). A some point, adding a somewhat different mission, it became simpler to take a subset of the original data and add just the additional items for the different mission. This repeatedly happening a number of times over a decade or more ... and the organization finds itself with 6000 very similar but still different deployments.

There are still some number of significantly large business operations which continue to find they aren't able to justify the move from IMS type infrastructures to RDBMS operation. For the most part the value of the operation easily justifies both the hardware and people costs ... and the aggregate data may be so large ... and access patterns are sparse enough that there is not high probability that significant amounts of (RDBMS) index would already be cached, to eliminate needing several disk operations to arrive at the desired record. In some cases the issue may be that they have elapsed time constraints (like overnight batch windows) where elapsed processing time and number of (serially ordered) disk I/Os represents a significant consideration.

Periodically there are statements that there may still be more aggregate data in these types of respositories than aggregate data existing in RDBMS repositories.

misc. past posts mentioning system/r
http://www.garlic.com/~lynn/subtopic.html#systemr Received on Thu Mar 01 2007 - 18:37:44 CST

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