Re: Serializability of Transactions and Automatic (Number) Generators

Paul wrote:

> Wouldn't any abstract identifier stored on a computer end up with a
> default ordering in the minds of users though? Because underneath, it
> will be always be stored as numbers (e.g. the ASCII codes).

i probably shouldn't try to answer this (not qualified!) but i can't resist: I suspect that 'in the minds' depends on one's culture. Not that i know enough about other cultures to say otherwise, but i wouldn't assume this.

of course on that score, pretty much any of today's products as well as TTM could be criticized for their use of English-language-based verbs rather than inventing completely new symbols. i'd bet there are few people even among the readers of this high-brow group who haven't been fooled once or twice by the connotations of words like 'AND' and 'COMMIT' and 'ROLLBACK'.

> How would you have get a totally abstract identifier that has no
> ordering baggage coming along with it?

i presume that you are talking about ensuring that the RM has no dependency on ordering. i have never seen any real rationale for this restriction (even though i agree with it). i have always assumed that Codd was trying to avoid baggage of another kind - namely IMS's where a child segment that followed (in storage or in a navigation path) a certain parent segment was inferred to be that parent's child!

maybe he had in mind avoiding effects of collation too, but if he did, i'd say that the behaviour of domains (ie. types) very much overrides such effects, since it is a psychological choice (from the DB's perspective) how we choose to define the operators on a domain (eg. we might choose to not define a 'less than' operator).

avoiding verbs like 'GET FIRST' and 'GET LAST' may also have been his intent, since these would require the RM to assume that all domains would support an ordering sufficient to satisfy those verbs. i wish Date or somebody would write an article about this, in case i've got it wrong.

personally, i still don't see the connection between the use of integers to make a definition of RM and the RM itself depending on any internal ordering. for that matter, as somebody else on this thread pointed out, i don't even see that the definition (as opposed to the RM itself) is dependent on ordering - you could reverse the ordering of the integers and the definition would define the same thing. The sequence of integers in the definition seems to be merely a short-cut to avoid enumeration.

(this took more words than i thought it would - sorry!)

magoo Received on Sun Dec 05 2004 - 02:17:11 CET