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Explain data abstraction?
Data abstraction Data abstraction is a methodology in which enables us to isolate how a compound data object is utilized from the details of how it is constructed from more primitive data objects.
What are the various symbols used to draw an E-R diagram? Explain with the help of an example how weak entity sets are represented in an E-R diagram. Various symbols used to d
Define Serializable schedule Serializable schedule: An interleaved schedule of much more than one transaction is known as a serializable schedule, if it is equal to some serial
What is a SELECT operation? The select operation selects tuples that please a given predicate. We use the lowercase letter σ to denote selection.
What is the difference between WHERE and HAVING clauses?. Predicates in the WHERE clause applies to every tuple while the predicate in the HAVING clause applies to groups.
Column Constraints: NOT NULL, UNIQUE, CHECK, PRIMARY KEY, DEFAULT, REFERENCES, On delete Cascade : Using this key whenever a parent row is removed in a referenced
Attribute Preservation This is a easy and obvious necessity that includes preserving all the attributes that were there in the relation that is being decomposed.
CREATE TABLE prodtrans ( pno number (4) ptype char (1) CHECK (ptype in ('I','R','S')), qty number (5) FOREIGN KEY pno REFERENCES product (pno) ON DELETE CASCADE);
Object-oriented decompositions Object-oriented decompositions of systems better are able to cope with change. Each subsystem has a well-defined interface which communicates with
Do NOT use the timestamp type. Use separate date and time data types only. Figure out how to define an SQL insert statement that uses built-in SQL (or MySQL) functions to define
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.
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