Three-way Junction Table OK? or is it an entity?

Question

Is a Junction Table with three Primary/Foreign Keys allowable? Or does does my original Junction Table linking just two Tables become an entity when I add the third primary/Foreign key.

I need to know whether it's an entity or a three way Junction Table because junction tables are not displayed on E.R. diagrams.

Answer 1

The type of relationship you are describing is called a Ternary relationship. In an ER diagram you would draw it as the rhombus sign connecting 3 entities.

I could explain it here but a better explanation with examples and also possible ways to consider converting a ternary relation to a set of binary relations is described here: http://www.databasedesign.co.uk/bookdatabasesafirstcourse/chap3/chap3.htm