Cross Product is a:
Answer: C
Correct answer: Binary Operator
The Cartesian product takes two relations and returns one, so it is a binary operator - as are union, difference, intersection and join. Selection and projection are unary, taking a single relation.
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In __________ data can be stored in structured manner.
Answer: C
Correct answer: Database
A database stores data in a structured way: organised into tables of typed columns, with keys and defined relationships between them. The CPU and ALU are processing hardware and store nothing of the kind.
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What is a relationship called when it is maintained between two entities?
Answer: B
Correct answer: Binary
A relationship’s degree is the number of entity types it connects: binary for two, unary (recursive) for one entity type related to itself, ternary for three. Binary relationships are much the most common.
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Database applications are seldom intended for use by a single user.
Answer: B
Correct answer: False
Plenty of database applications are meant for a single user - a personal contact list, a small stock record, most Access databases. The multi-user case is the harder and more interesting one, but it is not the only one.
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Consider the join of a relation R with relation S. If R has m tuples and S has n tuples, then the maximum size of join is:
Answer: A
Correct answer: mn
A join is a selection applied to the Cartesian product, so it can never return more tuples than the product itself, which has \(m \times n\). That maximum is reached only when the join condition matches every pair - in effect a cross join. A typical equijoin on a foreign key returns far fewer.
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Which of the following is another name for weak entity?
Answer: A
Correct answer: Child
A weak entity has no key of its own and depends on an owner for its identity, so it is also called the child or subordinate entity; the entity it depends on is the owner, parent or dominant one. A loan payment identified only by its number within a given loan is the classic example.
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The database environment has all of the following components except:
Answer: B
Correct answer: Separate files
The database environment consists of users, applications, the DBMS, the database and the database administrator. Separate files are precisely what it replaces - the pre-database arrangement, in which each application kept its own file and the same data was duplicated and grew inconsistent.
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A DBMS query language is designed to
Answer: D
Correct answer: All of the above.
A query language covers all three: ad hoc questions in near-English for end users; the data manipulation that application code is built on; and, through its data definition part, the structure of the database itself. SQL is the obvious example - SELECT, INSERT and CREATE TABLE all belong to it.
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SQL stands for ________ .
Answer: A
Correct answer: Structured Query Language
SQL is Structured Query Language. It came out of IBM’s System R project as SEQUEL and was standardised by ANSI in 1986; it covers not only queries but also data definition, updates and access control.
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Because it contains a description of its own structure, a database is considered to be ________ .
Answer: C
Correct answer: self-describing
A database stores metadata - the definitions of its own tables, columns, keys and indexes - alongside the user data, in system tables that can be queried like any other. That is what makes it self-describing, and it is why a tool can connect to an unfamiliar database and discover its structure without being told.
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