Database Management ch 3

Primary key

a candidate key selected to uniquely identify all other attribute values in a given row

attribute

a characteristic of an entity

referential integrity

a foreign key that contains a value that matches an existing valid row in another table to which its related, or has a null entry

entity relationship model

a graphical representation of entities and their relationships for Relational Model

composite key

a key many be composed of more than one attribute

Candidate key

a minimal superkey. a superkey without unnecessary attributes

constraint

a restriction placed on data

Entity integrity

all primary keys are unique, no part of a primary key may be null

foreign key

an attribute (or combination of attributes) in one table whose values must either match the primary key in another table or be null

superkey

an attribute(or combination of attributes) that uniquely identifies each row in a table

Entity Requirements

an entity should have many instances(occurrences/rows); an entity should have many interesting attributes. Each table must have an attribute or a combination of attributes that uniquely identifies each row

key attribute

any attribute that is part of a key

entity

anything about which data is to be collected and stored

functional dependence

attribute B is functionally dependent on A if all rows in the table that agree in value for A also agree in value for B

composite entity

composite entity's primary key=the combination of the foreign keys of tables to be linked

business rulesq

descriptions of policies, procedures, and principles within a specific organization. Sources include: company managers, policy makers, department managers, written documentation

Entity Relationship Diagram

entity is mapped to a relational table; entity instance/occurrence is row in the table; entity set is a collection of linked entities

M:N relationship

implemented by breaking it up to produce a set of 1:M relationships ; avoid the problems of M:N relationship by creating a composite entity

Data model components

include entities, relationships, attributes

unique index

index in which the index key can only have one pointer value(row) associated with it

index key

index's reference point; points to data location identified by the key

table

matrix consisting of row/column intersections; each row in a relation is called a tuple

1:1 relationship

one entity related to only one other entity, and vice versa; sometimes means that entity components were not properly defined; could indicate that two entities belong in the same table

key

one or more attributes that determine other attributes; role is based on determination

1:M relationship

relational model ideal that should be the norm in any relational database design