What is relvar - relational variable?

Question

I am reading an introductory book on database systems and the authour introdiced the term: relational variable - relvar.

It says that the relvar is a container for the actual relation.

What is it meant by container? Is this a pysical concept, like a place on disk? Is this more of an logical concept, so that container is just an umbrella term for metadata and relation?

Answer 1

A relation variable can be contrasted with a relation value. These concepts are analogous to simple algebraic variables like x, and values like 5.

A relation variable is a symbol that can reference different values at different times - hence the term variable, since its value can vary. For example, I might have a relation Employee which holds information about the people working for me at any given time.

A relation value is a particular state. Values don't vary. When we say the value of a variable changes, we actually mean that the variable is assigned a new value, which may be derived from the old value.

These are logical concepts. Container is an informal term which is accessible to a lay audience. However, it shouldn't be taken too literally. Variables and values can be implemented or represented in a variety of ways in physical systems.