mis 160 ch 9

Data type

- A coding scheme recognized by system software for representing organizational data.

Calculated field

- A field that can be derived from other database fields.

Recursive foreign key

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

Physical table

- A named set of rows and columns that specifies the fields in each row of the table.

2NF

- A relation for which every nonprimary key attribute is functionally dependent on the whole primary key.

Normalization

- The process of converting complex data structures into simple stable data structures.

Synonym

- Two different names that are used for the same attribute.

Referential integrity

An integrity constraint specifying that the value (or existence) of an attribute in one relation depends on the value (or existence) of the same attribute in another relation.

Hashed file organization

The address for each row is determined using an algorithm.

Field

The smallest unit of named application data recognized by system software.

Physical file

- A named set of table rows stored in contiguous section of secondary memory.

Functional dependency

- A particular relationship between two attributes.

3NF

- A relation that is in second normal form and that has no functional (transitive) dependencies between two (or more) nonprimary key attributes.

Homonym

- A single attribute name that is used for two or more different attributes.

Null value

- A special field value distinct from a zero blank or any other value that indicates that the value for the field is missing or otherwise unknown.

Default value

- A value a field will assume unless an explicit value is entered for that field.

Primary Key

- An attribute whose value is unique across all occurrences of a relation

Foreign key

- An attributes that appears as nonprimary key attribute in one relation and as a primary key attribute ( or part of a primary key ) in another relation.

Pointer

A field of data that can be used to locate a related field or row of data.

Relation

A named two-dimensional table of data. Each relation consist of a set of named columns and an arbitrary number of unnamed rows.

Well- structured relation

A relation that contains a minimum amount of redundancy and allows users to insert, modify, and delete the rows without errors or inconsistencies.

Denormalization

The process of splitting or combining normalized relations into physical tables based on affinity of use of rows and fields.

Indexed file organization

The rows are stored either sequentially or nonsequentially and an index is created that allows software to locate individual rows.

Sequential file organization

The rows in the file are stored in sequence according to a primary key value.

Index

A table used to determine the location of rows in a file that satisfy some condition.

File organization

A technique for physically arranging the records of a file.

Relational database model

Data represented as a set of related table or relations.

Secondary Key

One or a combination of fields for which more than one row may have the same combination of values.