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What is a Database?
To know what database is, we have to start from data, which is the basic building block of any DBMS.
Data: Facts, figures, statistics etc. having no particular meaning (e.g. 1, ABC, 19 etc).
Record: Collection of related data items, e.g. in the above instance the three data items had no meaning. But if we organize them in the following way, then they collectively show meaningful information.
Record based Logical Models: Use records as the key data representation components Examples: Relational Model: It shows data as well as relationship between data in the form
List the Armstrong's axioms for functional dependencies. What do you understand by soundness and completeness of these axioms? Ans: The Armstrong's axioms are: F1:
Explain the Cascadeless Schedule A cascadeless schedule is one in which for every pair of transactions Ti and Tj like that Tj reads a data item before written by Ti, the commit
Briefly describe concurrency execution? Lock - based protocols Locks There are several modes in which a data item may be locked in this section we restrict our attention
The natural join is equal to which product? The natural join is equal to Combination of projection and Cartesian product
read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.
Define Assertions in SQL a. An assertion is a predicate that is expressing a condition we wish the database to always satisfy. b. Domain constraints, functional dependency
Examine about the Behavioural Diagrams The main objective of behavioural diagrams is to visualize, specify, construct and document dynamic aspects of a system. The interactio
Define physical image of a global relation at a site
Define weak and strong entity sets? Weak entity set: entity set that do not have key attribute of their own are known as weak entity sets. Strong entity set: Entity set that
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