The natural join is equal to :
Answer: C
Correct answer: Combination of selection and Cartesian product
A natural join is built from the basic operators: form the Cartesian product of the two relations, then select the tuples whose common attributes are equal - and finally project away the duplicated columns. That is why the join is a derived operation rather than a primitive of relational algebra.
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The way a particular application views the data from the database that the application uses is a
Answer: D
Correct answer: Sub schema.
A subschema (external schema) is one application’s view of the database: the subset of tables and columns it needs, possibly renamed or restructured. Several subschemas can sit over one logical schema, which is how different applications share the same data while each seeing only its own part.
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Which of the operations constitute a basic set of operations for manipulating relational data?
Answer: C
Correct answer: Relational algebra
Relational algebra is the procedural set of basic operations - selection, projection, union, set difference, Cartesian product, and the joins and intersection derived from them. Relational calculus is the non-procedural counterpart: it describes what is wanted rather than how to compute it, and the two have equivalent expressive power.
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Hierarchical model is also called
Answer: A
Correct answer: Tree structure
The hierarchical model organises records into a tree: every record type except the root has exactly one parent, and access is by navigating down from the root. That single-parent rule is its limitation - a many-to-many relationship cannot be represented without duplicating data - and it is what the network model, a “plex” or graph structure, was devised to relax.
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Relational Algebra is
Answer: C
Correct answer: Procedural query Language
Relational algebra is procedural: an expression specifies a sequence of operations - select, then project, then join - and so says how the result is to be obtained. Relational calculus and SQL are declarative by contrast.
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Key to represent relationship between tables is called
Answer: C
Correct answer: foreign key
A foreign key is a column whose values must appear as a primary key in another table, and that requirement is what represents the relationship between the two. A primary key identifies rows within one table only.
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DBMS should provide following feature(s) ______.
Answer: B
Correct answer: All of these
A DBMS must do all three: protect data against a system crash, through logging and recovery; keep the stored information safe, through backup and integrity constraints; and restrict access to authorised users. These are among the central reasons for using a DBMS instead of ordinary files.
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The property / properties of a database is / are :
Answer: D
Correct answer: All of the above
All three are defining properties. A database is an integrated collection of logically related records; it consolidates what used to be separate files into a common pool; and the data in it is independent of the programs that use it, so the storage can change without rewriting the applications.
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What does DDL stand for in SQL ?
Answer: A
Correct answer: Data Definition Language
DDL comprises the statements that define and alter database structure, such as CREATE, ALTER and DROP. DML, the Data Manipulation Language, covers the statements that work on the rows themselves.
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DBMS stands for __________.
Answer: D
Correct answer: Database Management System
DBMS is Database Management System: the software that stores, retrieves, updates and administers the data, and enforces the rules that keep it consistent.
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