Re: OOPs! James is confused again!
Date: Sat, 15 Jun 2002 01:05:53 -0400
Message-ID: <UYzO8.357$8u1.51765392_at_radon.golden.net>
> Yes, I think it is much easier for us to iron-out difference at the
> logical model. By the way what is a logical vs physical model?
Paraphrasing the ISO/IEC standard:
The logical level considers an abstract model of data. The physical level considers the concrete data structures, mappings to storage organizations and access operations in an actual computer system.
The type Integer is an abstract data type including all integer numbers. One might physically represent integer values as sequences of 32 or 64 bits. An index, a hash or a pointer is a mapping to storage that determine access operations.
In a relational dbms, all logical structures are relations, and the dbms maps these relations onto physical structures of any kind.
An rdbms might map a small, simple relation onto a single database page in the heap with no indexes. Or it might map data from two or more relations onto the same database pages (clustering order_item with order, for instance). Or a distributed rdbms might map data from a single relation onto multiple geographically distant computers. Received on Sat Jun 15 2002 - 07:05:53 CEST