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What is the difference between a key and a superkey?
Key - A key a single attribute or a combination of two or more attributes of an entity set which is used to identify one or more examples (rows) of the set (table). It is a minimal combination of attributes.
Super Key - A super key is a set of one or more attributes in which, taken collectively, permits us to identify uniquely a tuple within the relation.
(a) Explain the three types of potential mistake which could occur if concurrency control is not properly enforced in the database system. Support your answer with appropriate ex
Define canonical cover? A canonical cover Fc for F is a set of dependencies like F logically implies all dependencies in FC and Fc logically shows all dependencies in F.
What are the General Transformation Rules for Relational operations? Ans: The transformation rules transform one relational algebra expression to AN EQUIVALENT ONE 1. E
Consider the relation PERSON. If you want to display details of persons having age less than or equal to 30 than the select operation will be used as follows: σ AGE The resu
What is recovery management component? Ensuring durability is the responsibility of a software component of the base system known as the recovery management component.
Define granularity, hierarchy of granularity of locks & multiple granularity locking. Explain the modified two phase locking along with multiple granularity locking. Ans: The s
In the architecture of a database system which external level used? In the architecture of a database system view external level used.
Define the following constraints for the table client. (i) BAL_DUE must be at least 1000. (ii) NAME is a unique key. (i)ALTER TABLE CLIENT ADD CONSTRAINT CLIENT_BAL_DUE_C1
What is data model? Explain object based and record based data models? Ans: A data model is an abstract model in which describes how data is represented and accessed. (i)
List and also explain the dissimilar stages of DDLC ?
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