Chapter 3 Database Management

Composite Key

A key that is comprised of more than one attribute

Candidate Key

A minimal superkey that uniquely identifies a row

Determinant

An attribute that determines the value of another A --> B

Key attribute

Any attribute that is apart of a key

Superkey

Any key that uniquely identifies a row

Formal definition of a Candidate Key

Attribute K of Table R is a candidate key for R if it satisfies the following two time independent properties: Uniqueness - No two record occurrences of R have the same value of K Minimality - If K is composite, then it is a candidate key.

Primary Key

Candidate key that we choose to uniquely identify a row

External Model

End-user's view of the database environment Views showing using ERD's unlimited number of SubSchemas based on end-user requirements Independent of Hardware/Software Portion of the total database

ANSI SPARC

External Model, Conceptual Model, Internal Model Mapping between each level must be defined

Conceptual Model

Global view of the entire database ERD represents the conceptual schema Entire information content Macro level view Independent of Hard/Software

Formal definition of Foreign Key

Let R2 be a base table. Then a foreign key in R2 is a subset of the set of fields of R2, say FK, such that: There exists a base relation R1 with a candidate key CK, and For all time, each value of FK in the current value of R2 is either null or is identical to the value of CK in some record occurrence in the current value of R1

Referential Integrity

Must not contain any unmatched foreign key values Foreign keys must match primary keys or be null

Entity Integrity

No key attribute in the primary can contain a null value because a primary key must always be unique and a null value can never be unique

Internal Model

View seen by the DBMS Logical Independence Specific to software Hardware Independence