DBMS

41. Write short notes on tuple relational calculus. 

The tuple relational calculation is anon procedural query language. It describes the desired information with out giving a specific procedure for obtaining that information. 

A query or expression can be expressed in tuple relational calculus as 

{t | P (t)} 

which means the set of all tuples‘t’ such that predicate P is true for‘t’. 

Notations used: 

•t[A] ® the value of tuple ‘t’ on attribute, A 

•t Î r ® tuple ‘t’ is in relation ‘r’ 

•$® there exists 

Definition for ‘there exists’ ($): 

$ t Î r(Q(t)) 

which means there exists a tuple ‘t’ in relation ‘r’ such that predicate Q(t) is true. 

•"® for all 

Definition for ‘for all’ ("): 

"t .r(Q(t)) which means Q(t) is true for all tuples ‘t’ in relation ‘r’. 

• Implication 

Definition for Implication ( ): 

P Q means if P is true then Q must be true. 

42. Write short notes on domain relational calculus 

The domain relational calculus uses domain variables that take on values from an attribute domain rather than values for entire tuple. 

43. Define query language? 

A query is a statement requesting the retrieval of information. The portion of DML that involves information retrieval is called a query language. 

44. Write short notes on Schema diagram. 

A database schema along with primary key and foreign key dependencies can be depicted pictorially by schema diagram. Each relation appears as a box with attributes listed inside it and the relation name above it. 

45. What is foreign key? 

A relation schema r1 derived from an ER schema may include among its attributes the primary key of another relation schema r2.this attribute is called a foreign key from r1 referencing r2.