“Relation” versus “relationship” in RDBMS/SQL?

Question

Coming from question “Relation” versus “relationship”

What are definitions of \"relation\" vs. \"relationship\" in RDBMS (or database theory)?

Update:
I

Answer 1

Relation is a mathematical term referring to a concept from set theory. Basically, in RDBMS world, the "relational" aspect is that data is organized into tables which reflect the fact that each row (tuple) is related to all the others. They are all the same type of info.

But then, your have ER (Entity Relationship) which is a modeling methodology in which you identify objects and their relationships in the real world. Then each object is modelled as a table, and each relationship is modelled as a table that contains only foreign keys.

For instance, if you have 3 entities: Teacher, Student, Class; then you might also create a couple of tables to record these 2 relationships: TaughtBy and StudyingIn. The TaughtBy table would have a record with a Teacher ID and a Class ID to record that this class is taught by this teacher. And the StudyingIn table would have a Student ID and a Class ID to reflect that the student is taking this class.

That way, each student can be in many Classes, and each Teacher can be in many classes without needing to have a field which contains a list of class ids in any records. SQL cannot deal with field containing a list of things.