Ch 02: Prerequisites

Overview

Any given database consists of relation variables (rekvars for short)

The value of any given relvar at any given time is a relation value (relation for short)

Every relvar represents a certain predicate

Within any given relvar, every tuple represents a certain proposition.

In accordance with the the Closed World Assumption, relvar R at time T contains all and only those tuples that represent instantiations of the predicate corresponding to relvar R that evaluate to TRUE at time T.

…relations have two parts, a heading and a body. Basically the heading is a set of attributes, and the body is a set of tuple that conform to that heading.

Both RELVARs and RELATIONs have headings.

The heading of a RELVAR represents a predicate which in the intended meaning.

…a predicate isn’t really a statement as such, rather, it’s the assetion made by that statement.

Propositions can be true or false.