Can relation in Entity-Relationship diagram have an attribute which can be called as a primary key? Pardon me if it sounds silly!

no it's not silly, but no, i don't think relations have PKs

relations are FKs, ultimately

i realize that there are some ER diagramming conventions that have rectangles for entitites and diamonds for relationships, but that's too messy for me

the ER diagrams that i create simply have rectangles for entitites and lines connecting them for the relationships

among other things, this means i never draw a many-to-many relationship, but always use two one-to-many relationships with a "relationship" entity defined to carry the FKs

make sense?

Rudy - are you confusing relations and relationships here?

pootle flump ur codings are working excelent.

almost certainly

what's the difference?

The former are foisted up on you, the latter you get to choose.

Are you in an obtuse mood today or were you simply fishing?

pootle flump ur codings are working excelent.

got a vague picture though!

In the Barker ERD notation we Oracle types use, an Entity can have a Unique Identifier defined which may consist of one or more attributes and relationships. Relationships that are part of the Unique Identifier are marked with a bar at the end next to that entity.