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25 Cards in this Set
- Front
- Back
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True or false: The degree (or arity) of a relation is the number of fields.
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True
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True or false: an integrity constraint limits the data that can be viewed by a database user.
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False
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A superkey is...
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something that specifies no two distinct tuples in any state r of R can have the same value for SK
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What are the three levels of abstraction?
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Physical, conceptual, external
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What is a transaction?
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Manipulation of data
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What are the two kinds of data independence
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Conceptual. logical?
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What is program-data independence?
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The structure of the data is stored in the DBMS catalog separately from the access programs.
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What is atomicity?
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Either all of the transactions are completed or none are.
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What is the degree of a relation?
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The number of fields.
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What is a superkey?
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A superkey specifies a uniqueness constraint that no two tuples have the same values.
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What is cardinality?
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The number of records.
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What is the entity integrity constraint?
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No primary key value can be NULL.
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What is the referential integrity constraint?
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A tuple in one relation that refers to another must refer to an existing tuple.
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What is data independence?
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Hide data representation, hide data storage.
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What are advantages of a DBMS?
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Access control, centralized data administration, efficient data access, data independence, crash recovery, concurrent access, etc
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Disadvantages of a DBMS?
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High maintenance, high startup cost.
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What is meta-data?
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Describes structure of database.
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What is a tuple?
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A row of related data
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What is a domain?
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A set of atomic values.
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What is an integrity constraint?
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a condition specified on a database schema that restricts the data that can be stored in an instance and is enforced by the DBMS.
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What does it mean to be union-compatible?
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Same number of fields, same domain for every corresponding field.
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What is DDL?
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Data definition language
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What is DML?
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Data manipulation language
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What is SQL?
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Structured query language
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SQL statement to count the number of unique sailor names
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SELECT COUNT(distinct S.Sname) FROM Sailors S
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