Database Systems Ch 4-5

Relation

A named two-dimensional table of data.

Primary key

An attribute or a combination of attributes that uniquely identifies each row in a relation.

Composite key

A primary key that consists of more than one attribute.

Foreign key

An attribute in a relation that serves as the primary key of another relation in the same database.

Null

A value that may be assigned to an attribute when no other value applies or when the applicable value is unknown.

Entity integrity rule

A rule that states that no primary key attribute (or component of a primary key attribute) may be null.

Referential integrity constraint

A rule that states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null.

Well-structured relation

A relation that contains minimal redundancy and allows users to insert, modify, and delete the rows in a table without errors or inconsistencies.

Anomaly

An error or inconsistency that may result when a user attempts to update a table that contains redundant data. The three types of anomalies are insertion, deletion, and modification anomalies.

Surrogate primary key

A serial number or other system-assigned primary key for a relation.

Recursive foreign key

A foreign key in a relation that references the primary key values of the same relation.

Normalization

The process of decomposing relations with anomalies to produce smaller, well-structured relations.

Normal form

A state of a relation that requires that certain rules regarding relationships between attributes (or functional dependencies) are satisfied.

Functional dependency

A constraint between two attributes in which the value of one attribute is determined by the value of another attribute.

Determinant

The attribute on the left side of the arrow in a functional dependency.

Candidate key

An attribute, or combination of attributes, that uniquely identifies a row in a relation.

First normal form (1nF)

A relation that has a primary key and in which there are no repeating groups.

Second normal form (2nF)

A relation in first normal form in which every nonkey attribute is fully functionally dependent on the primary key.

Third normal form (3nF)

A relation that is in second normal form and has no transitive dependencies.

Partial functional dependency

A functional dependency in which one or more nonkey attributes are functionally dependent on part (but not all) of the primary key.

Transitive dependency

A functional dependency between the primary key and one or more nonkey attributes that are dependent on the primary key via another nonkey attribute.

Synonyms

Two (or more) attributes that have different names but the same meaning.

Non-Loss Decompositions

Decomposing a relation in a way that a join operation should restore the original information.

Field

The smallest unit of application data recognized by system software.

Data type

A detailed coding scheme recognized by system software, such as a DBMS, for representing organizational data.

Denormalization

The process of transforming normalized relations into nonnormalized physical record specifications.

Horizontal partitioning

Distribution of the rows of a logical relation into several separate tables.

Vertical partitioning

Distribution of the columns of a logical relation into several separate physical tables.

Physical file

A named portion of secondary memory (such as a hard disk) allocated for the purpose of storing physical records.

Tablespace

A named logical storage unit in which data from one or more database tables, views, or other database objects may be stored.

Extent

A contiguous section of disk storage space.

File organization

A technique for physically arranging the records of a file on secondary storage devices.

Sequential file organization

The storage of records in a file in sequence according to a primary key value.

Indexed file organization

The storage of records either sequentially or nonsequentially with an index that allows software to locate individual records.

Index

A table or other data structure used to determine in a file the location of records that satisfy some condition.

Secondary key

One field or a combination of fields for which more than one record may have the same combination of values. Also called a nonunique key.

Pointer

A field of data indicating a target address that can be used to locate a related field or record of data.