Re: Sensible and NonsenSQL Aspects of the NoSQL Hoopla

From: <compdb_at_hotmail.com>
Date: Wed, 28 Aug 2013 15:54:31 -0700 (PDT)
Message-ID: <44c03f41-91c7-45ae-9beb-93f205a28dba_at_googlegroups.com>


On Monday, August 26, 2013 3:20:44 AM UTC-7, karl.s..._at_o2online.de wrote:
> What is the benefit of "logical model" that cannot be mapped lossless to
> a physical storage? Sorry, but relations are abstractions of "record
> oriented" storages.

You have a misconception of the relational model. A relational schema is intended to express what you call a "conceptual model". A relation variable or query has an associated predicate and its tuples are those that make true propositions/statements.

The notion of distinct "conceptual" and "logical" models is a perversion that arose from non-relational thinking. Even ORM2/FCO-IM, which has always made an effort to map directly to a relational schema, is an unnecessary layer in the sense that only the relational schema, its "logical" model, ends up being the form of the model one actually uses. (With its conceptual a relational view of its logical.) You seem to be misinformed in a typical ER culture way, where a relational schema is wrongly taken to be a sort of implementation data structure. (And the role of constraints is not understood.)

The point of the relational model is that when one's model is a relational schema, which as I say includes predicates about the world (from which constraints follow), one can query directly about that world generically in terms of those predicates (either via predicate logic formulas or equivalent relation expressions) with an automatic optimized execution.

philip Received on Thu Aug 29 2013 - 00:54:31 CEST

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