21.  What is an attribute?

22.  What is a Relation Schema and a Relation?

23.  What is degree of a Relation?

24.  What is Relationship?

25.  What is Relationship set?

26.  What is Relationship type?

27.  What is degree of Relationship type?

28.  What is DDL (Data Definition Language)?

29.  What is VDL (View Definition Language)?

30.  What is SDL (Storage Definition Language)?