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A DBMS is a software package that carries out many different tasks including the provision of facilities to enable the user to access and modify information in the database.
What is functional dependency? What is the need for normalization? Explain 2nd and 3rd normal form with example. Consider the following relation:
EMP_PROJ { SSn, Pnumber, Hours, Ename, Pname, Plocation}
Assume { SSn, Pnumber} as primary key. The dependencies are
{SSn, Pnumber}→ Hours; SSn →Ename; Pnumber → {Pname, Plocation}.
Normalize the above relation into 2NF.
Let Χ and Υ be the arbitrary subsets of a set of attributes of a relation schema R, then an instance r of R satisfies FD X →Y , if and only if for any two tuples t1 and t2 in r that
Let R (ABCDE) be a relation schema and consider the following functional dependencies F = { AB→ E, AD→B, B→ C, C →D}. Find out the candidate key.
Case 1: as B→C and C→D, so B→D (transitivity)
Define a Foreign key. Why is the concept needed? How does it play a role in the join operation?
A relation, say, r1, may include among its attributes the primary key of another relation, say, r2. This attribute in called a foreign key
Explain View with suitable example. What is the usefulness of a view?
View is the simply subset of table which are stored logically in a database means a view is a virtual table in the database whose contents are defined by a query.
Design a Generalization- Specialization hierarchy for a motor vehicle sales company. The company sells motor-cycles, passenger cars, vans, buses. Justify your placement of attributes at each level of the hierarchy. Explain why they should not be placed at a higher or lower level.
The process of generalizing entities, where the generalized entities contain the properties of all the generalized entities, is called generalization.
What are the differences between Primary Index, Secondary Index, and Clustering Index?
Indexing is a data structure technique to efficiently retrieve records from the database files based on some attributes
Let T1, T2, T3 be transactions that operate on the same data items A, B, C. Let r1(A) means that T1 reads A, w1(A) means that T1 writes A and so on for T2 and T3. Consider the following schedule: S1: r2(C), r2(B), w2(B), r3(C), r1(A), w1(A), w3(B), w3(C), r2(A), r1(B), w1(B), w2(A). Is the schedule serializable and why?
A precedence graph, also named conflict graph and serializability graph, is used in the context of concurrency control in databases.
Define BCNF. How does it differ from 3NF? Why is it considered stronger than 3NF?
A relation is in BCNF, if and only if, the relation is in 3NF and every determinant is a candidate key.
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