Re: Question on Structuring Product Attributes

On Saturday, February 16, 2013 4:20:01 PM UTC-7, paul c wrote:
> On 14/02/2013 8:03 PM, James K. Lowden wrote: > SQL was intended, I'm sure you agree, to be a language for deriving logical inferences.
[omitted text].

Something that never seems to get addressed is the pre-history of DB technology before Codd, before SQL. Within that universe, IMS and IMS-like databases were used much as today to track the state of some model, but were queried by a mechanism called RPG (for Report Program Generator). The RPG spec could be given within COBOL or in a standalone interface, but the idea was to spit out retrieved data in a report formed as the interpretive software made a single pass over the linearized physical (after RDBMS, logical) order of the records, or segments as they were called. Any sorts or aggregates were computed after-the-fact from an intermediate containing the retrieved data in the logical/physical order in which it was accumulated.

So when the System R folks at IBM were defining Sequel (which became SQL), the objective was not logical inference, it was report-writing. After all, the whole point of Codd's thrust was to replace IMS (et. al.) with a system that was immune to changes in the physical storage structure of the data. But that didn't obviate the major purpose of such databases, report-writing If you examine the most primitive SQL form of the SELECT statement, it is a non-procedural specification of a traversal of the logical product (in the FROM clause) to retrieve the attributes (in the SELECT clause) restricted by the predicate of the WHERE clause). And again, sorted (as specified in the ORDER clause), formatted and aggregated (SELECT clause again).

Database technology has come a long way since the 1970s when SQL was initially specified, and relational DBMSs do alot more than report-writing. But to suggest that in the 1970s, the authors were interested in "logical inference" requires great poetic license compared to "replacing the report-writer capabilities of IMS", and feels like history rewritten.

Rob Received on Sun Feb 17 2013 - 03:30:04 CET