Chapter 9 System Analysis and Design

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.

Functional dependency

A particular relationship between two attributes.

Input mask

A pattern of codes that restricts the width and possible values for each position of a field.

Second normal form (2NF)

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

Well-structured relation (or table)

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

Third normal form (3NF)

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

Field

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

Synonyms

Two different names that are used for the same attribute.

Pointer

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

Calculated (or computed or derived) field

A field that can be derived from other database fields.

Physical file

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

Relation

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

Primary key

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

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.

Secondary key

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

Hashed file organization

The address for each row is determined using an algorithm.

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 non-sequentially, 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.

Data type

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

Homonym

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

Null value

A special field value, distinct from 0, blank, or any other value, that indicates that the value for the field is missing or otherwise unknown.

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.

Foreign key

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

Relational database model

Data represented as a set of related tables or relations.

Normalization

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

Default value

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