Chapter 2 Database

a table with columns and rows

Attribute

Set of allowable rules for once or more attributes

name of row

number of attributes

number of tuples

set of attribute and domain name pairs

eg; RelationName (attribute1)

set of relation schemas,

a tuple at a specific moment of time

- relation name is distinct

- each cell rotation contains one value

- attribute name is distinct

- value of attributes are all from same domain

- tuple is distinct

- order of attributes no significance

- order of tuples no significance

one or more attributes in a relation that uniquely identifies each tuple in a relation

attribute or set of attributes that uniquely identifies a tuple within a relation

a superkey with no proper subset within the relation

•(uniqueness).

• (irreducibility).

•If subset of K is a superkey itself, then K is not a candidate key

•one candidate keys in a relation

key consists of more than one attribute

candidate key that is selected to identify tuples uniquely within the relation

candidate keys that are not selected to be primary key

an attribute, or set of attributes within one relation that matches the primary key of one relation.

to ensure correctness/accuracy of data

constraints or restrictions that apply to all instances of the database

entity integrity, referential integrity

• value for tuple unknown.

•Deals with incomplete or exceptional data.

•Represents the absence of a value and is not the same as zero or spaces, which are values

in base relation, no attribute of primary key can be null

If foreign key exists in a relation, the foreign key value:

1.must match a candidate key value of some tuple in its home relation; OR

2.foreign key value must be wholly null.

additional rules specified by user or database admins that define or constrain some aspect of the enterprise

named relation corresponding to an entity in a conceptual schema, whose tuples are physically stored in the database

•The dynamic result of one or more relational operations operating on base relations to produce another relation

•A virtual relation that produced upon request.

•Contents of a view are defined as a query on one or more base relations.

•Dynamic - changes made are immediately reflected

•Provides powerful and flexible security mechanism by hiding parts of database from certain users.

•Permits users to access data in a customized way, so that same data can be seen by different users in different ways, at same time.

•Can simplify complex operations on base relations.

updates to a base relation should be immediately reflected in all views that reference that base relation.

•Updates are allowed if query involves a single base relation and contains a candidate key of base relation.

•Updates are not allowed when query involves multiple base relations.

•Updates are not allowed when query involves aggregation or grouping operations.