Set difference, Database Management System

Set Difference

If R1 and R2 are two union compatible relations or relations then result of R3 =R1- R2 is the relation that have only those tuples that are in R1 but not in R2.

Incase, R3 will have tuples such that R3 = {t | R1 ∋ t ∧ t∉R2}.

 

Example:

 

R1

 

X

Y

A1

B1

A7

B7

A2

B2

A4

B4

 

 

 

  R2  

A

B

A1

B1

A2

B2

A3

B3

A4

B4

 

 

R1-R2 =

 

 

 

R1-R2 =

A

B

A3

B3

 

R2-R1=

 

 

 

R2-R1=

A

B

A7

B7

 

 

 

Note: -1) Difference operation is not commutative, i.e.,

 R1 - R2 ≠ R2 - R1

2) Difference operation is not associative, i. e.,

R1 - (R2 - R3) ≠ (R1 - R2) - R3

Posted Date: 3/6/2013 5:46:06 AM | Location : United States







Related Discussions:- Set difference, Assignment Help, Ask Question on Set difference, Get Answer, Expert's Help, Set difference Discussions

Write discussion on Set difference
Your posts are moderated
Related Questions
Give the reasons for allowing concurrency? The reasons for allowing concurrency is if the transactions run serially, a short transaction might have to wait for a preceding long

a publishing company produce scientific books on various subjects. the books are written by authors who specialize in one particular subject. the company employs editors who, not n

Question: (a) List four disadvantages of the File Processing System as compared to the Database Systems. (b) The integrity of a database is enforced by integrity rules. One

How to define a job scheduling strategy that will meet business requirement of reporting availability by 6am CST for the following cubes? Show the job scheduling dependencies in a

Data Redundancy -A lot of information is being repeated in the relation. For instance, the information that MCS-014 is named SSAD is repetitive, address of Rahul is "D- 27, Main ro

Compare wait-die deadlock prevention scheme with wait-wound scheme   Ans:  Wait-Die Scheme  a) Based upon a nonpreemptive technique.  b) If Pi requests a resource present

A Distributed Transaction Let us demonstrate the concept of a distributed transaction by considering a banking system having of three branches located in 3 different cities. Ev

(a) Why did SAP introduce the extended star schema?

Describe Physical Data independence ? Physical Data Independence - It is capacity to modify the internal schema without having to change conceptual schema. Therefore, the exter

what is the need of a log in dbms