Modern Systems Analysis and Design Chp 9

Second normal form (2NF)

A relation is in second normal form if every non primary key attribute is functionally dependent on the whole primary key. Satisfied if one of the following conditions apply: 1. The primary key consists of only one attribute 2.No non primary key attributes exist in the relation 3. Every non primary key attribute is functionally dependent on the full set of primary key attributes.

Referential integrity

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 (have no value). one of the most important principles of the relational model.

Null value

A special field value, distinct from 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 ( or combination of attributes) whose value is unique across all occurrences of a relation. Indicated by an underline

Range partitioning

Partitions are defined by nonoverlapping ranges of values for a specified attribute. (so seperate tables are formed of the rows whose specified attribute values fall in indicated ranges)

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, designate by a dashed line.

Composite partitioning

combines range and hash partitioning by first segregating data by ranges on the designated attribute, and then withing each of these partions, it further partitions by hashing on the designated attribute.

Secondary key

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

Partitioning

the capability to split a table into seprate sections

synonym

two different names that are used for the same attribute

Indexed file organization

A file organization in which rows are stored either sequentially or non sequentially, and an index is created that allows software to locate individual rows.

Sequential file organization

A file organization in which rows in a file are stored in sequence according to a primary key value.

Physical table

A named set of rows and columns that specifies the fields in each row of the table. two goals: efficient use of secondary storage and data processing speed.

Relation

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

Third normal form (3NF)

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

Range control

Both numeric and alphabetic data may have a limited set of permissible values

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

Denormalization

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

Field

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

Data type

a coding scheme recognized by system software for representing organizational data. Selecting a data type balances four objectives: 1. minimize storage space 2. Represent all possible values of the field 3. improve data integrity for the field. 4. support all data manipulations desired on the field.

Functional dependency

a constraint between two attributes in which the value of one attribute is determined by the value of another attribute. (employee ID to Name of employee, only one employee can have that ID)

Pointer

a field of data that can be used to locate a related field or row of data. (most cases address of associated data)

Calculated field

a field that can be derived from other database fields. Also known as a computed field or a derived field. (Birthdate and age)

Hashed file organization

a file organization in which the address of each row is determined using an algorithm.

Recursive foreign key

a foreign key in a relation that references the primary key values of that same relation. (two primary keys)

Physical file

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

Well structured relation

a relation that contains a minimum amount of redundancy and that allows users to insert, modify, and delete the rows without error or inconsistencies; also known as a table.

Homonym

a single attribute name that is used for two or more different attributes. (account can be checking, saving, or loan account)

Hash partitioning

a table row is assigned to a partition by an algorithm and then maps the specified attribute value to a partition.

Index

a table used to determine the location of rows in a file that stisfy some condition

File organizaation

a technique for physically arranging the records of a file.