CIS305_ch.5

data are organized in the form of tables with rows an dcolumns

powerful operations (using the SQL language) are used to manipulate data stored in the relations

facilities are included to specify business rules that maitain the integrity of data when they are manipulated

a named two-dimensional table of data

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

a primary key that consists of more than one attribute

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

• the set of values that may be assigned to an attribute.
• all of the values that appear in a column of a relation must be taken from the same domain.

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

no primary key attribute (or component of a composite primary key) may be null

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

a relation that contains minimal redudndancy an dallows users to insert, modify, and delete the rows in a table withoout errors or inconsistencies

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

entities that have an independent existence and generally represent real-world objects, such as persons and products. Regular entity types are represented by rectangles with a single line

entities that cannot exist except with an identifying relationship with an owner (regular) entity type. Weak entities are identified by a rectangle with a double line

(gerunds) are formed from many-to-many relationships between other entity types. associative entities are represented by a rectangle with rounded corners

• 1. Map regular entities
• 2. Map weak entities
• 3. Map binary relationships
• 4. Map associative entities
• 5. Map unary relationships
• 6. Map ternary (and n-ary) relationships
• 7. Map supertype/subtype relationships

a serial number or other system assigned primary key for a relation

a foreign key in a relation that refernces the primary key values of that same relation