Which of the following concurrency control schemes is not based on the serializability property?
Answer: D
Correct answer: None of these .
All three schemes exist to guarantee serializability: two-phase locking and the tree protocol enforce it by the order in which locks are taken, and timestamp ordering by comparing transaction timestamps. So none of them is the odd one out.
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The common column is eliminated in
Answer: C
Correct answer: natural join
A natural join matches on the columns the two relations share and then keeps only one copy of each such column. A theta join keeps both copies, since its condition need not be equality at all.
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The middleware databases in which the business rules act are applicable to _______ tier architectures
Answer: B
Correct answer: Three
A three-tier architecture separates presentation, application logic and data. The business rules live in the middle tier, which is what distinguishes it from two-tier, where the client holds them and talks to the database directly.
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The data models defined by ANSI/SPARC architecture are
Answer: D
Correct answer: Logical, physical and view
The ANSI/SPARC three-schema architecture has an internal or physical schema, a conceptual or logical schema, and external or view schemas - one per user group. Separating them is what makes data independence possible.
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Which among the following field type can store maximum data?
Answer: D
Correct answer: Memo fields
A Memo field holds long text - up to 65,535 characters - against a Text field's 255. Date/Time and Yes/No fields hold a fixed few bytes each.
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In SQL, testing whether a subquery is empty is done using
Answer: D
Correct answer: EXISTS
EXISTS takes a subquery and yields true if it returns at least one row, so NOT EXISTS tests emptiness. DISTINCT and UNIQUE concern duplicates and NULL tests a single value.
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Which of the following is not a recovery technique?
Answer: C
Correct answer: Two-phase commit
Deferred update, immediate update and shadow paging are all recovery techniques. Two-phase commit is a protocol for making a distributed transaction commit consistently across several sites - a concurrency and coordination problem rather than recovery from failure.
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The ______ approach reduces the time and effort required for design and carries less risk in database management.
Answer: B
Correct answer: Multiple databases
Splitting the design into several smaller databases means each can be designed, tested and changed on its own, so less has to be got right at once and a mistake affects less. A single global database has to be designed as one piece, which is both slower and riskier.
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____ table store information about database or about the system.
Answer: B
Correct answer: System
System tables, also called the catalogue or data dictionary, hold the database's description of itself - the tables, columns, indexes, users and permissions that exist. They are how the DBMS knows what it is managing.
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Relationships among relationships can be represented in an-E-R model using
Answer: A
Correct answer: Aggregation
Aggregation treats a relationship as though it were an entity, so that a further relationship can be attached to it. Without it there is no way to relate one relationship to another.
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