data integrity an empty database is a correct database

Data Integrity

An empty database is a correct database

Overview

• Review

• Domains

• What are integrity constraints?

• Gulf between the theory and the implementation

• Testing insertions into database?

• NULLS

Review

• Tuple

• Cardinality

• Attribute

• Degree

• Domain

Domains• Conceptual pool of values from which one

or more columns draw their values• Named set of scalar values all the same type

– scalar is smallest semantic unit of data, individual data value

• CREATE DOMAIN …? ?• Domain contains ALL permitted values,

static• Which relations in the database contain any

information pertaining to suppliers?

Comparisons with Domains• Domains constrain comparisons, = ,<>• domain-check override Codd• Logically equivalent statements must have

same semantic interpretation • Logic cannot be nullified

a = c Tb = c Ta = b F

• Arithmetic operators

Data Types

• Hide complexity within domain

• DATE domain

– three integers (d,m,y)

– interpreted by operators

• Address domain

– USA - street, city, state, zip

ADT in Oracle

• Simulate a domain• CREATE TYPE ADDR_TY AS OBJECT

– (STREET VARCHAR2(50),– CITY VARCHAR2(25),– STATE CHAR(2),– ZIP VARCHAR(9));

• CREATE TABLE NEW_CUSTOMER– ( CUSTID VARCHAR2(9) PRIMARY KEY,– CUST_NAME VARCHAR2(25),– ADDRESS ADDR_TY);

Relations• Abstract object• A relation, r, on a collection of domains, D1, D2

…Dn consists of two parts a heading and a body– heading - fixed set of attributes, <attribute-

name:domain-name> pairs

– body - set of tuples, <attribute-name:attribute-vale> pairs

• Named relation is really a variable• Relations dynamic• Table is concrete picture

Candidate Keys

• Subset of all attributes that are– Unique– Irreducibile

• Does not relate to current data set but to set of ALL POSSIBLE values– simple– composite

• Provide tuple-level addrressing mechanism• Primary key is selected from candidate key.

Others called Alternate keys

Is our information Correct ?

Consistent ?Logical ?

Start with a consistent database

Update the database

Result a consistent database

Is the data consistent?

Is the data consistent between tables? Are the same values equivalent? Do foreign keys reference existent primary

keys?Has logical consistency been

maintained?Have the business rules been enforced?All constraints valid?

How do we maintain correct, consistent data ?

Data Integrity Rules– Candidate keys– Domains

Referential Integrity Rules– Foreign keys

Business Rules– Constraints– Stored Procedures, Triggers

Where do we maintain correct, consistent data ?

• Database creation– base tables– views

• Implementation– back end– front end applications– middleware

Integrity rules are database specific

Foreign Keys

• If the foreign key contains either matching values or nulls, the table(s) that make use of such a foreign key are said to exhibit referential integrity.

• An attribute in one table refers to a primary key in another table– can it be a candidate key?– can it be the same table?

• A FK is composite if the primary key is composite.Referential Integrity assures that no invalid foreign keys permitted

• Relationships formed through foreign keys but not exclusively

Maintaining Integrity with Foreign Keys

Correct DBCorrect DBTransform thru update

•Delete Parent•restrict•cascades

•Update Parent•restrict•cascade

•How many levels of cascade?•Define procedures

Note: Correct database satisfies logical AND of all known rules

Entity Integrity• No component of the primary key of a base

relation is allowed to accept NULLS.

• In a relational database, we never record information about something we cannot identify.

• No attribute included in composite primary key can be NULL.

• Can alternate keys have NULLS?

Null Foreign Keys

• Can a foreign key be null?– definition - matches primary key or is null

• Can a composite foreign key have some attributes null?

• ON DELETE SET NULL– allows child record to remain but deleted key

attribute becomes null

Rules or Constraints• Theory

– CREATE INTERGIRTY RULE PR4• FORALL PX(PX.WEIGHT>0)• ON ATTMPTED VIOLATION REJECT;

• Oracle– CREATE TABLE PX ...

• WEIGHT NUMBER• CONSTRAINT PR4• CHECK (WEIGHT >0);

• Components name, truth-statement, violation response

Relation Rules or Constraints

• Theory– CREATE INTERGIRTY RULE SR8

• FORALL S(IF S.CITY = ‘LONDON’ THEN S.STATUS = 20)

• ON ATTMPTED VIOLATION REJECT;

• OracleMust be closed WFF

Database Rules

• CREATE INTEGRITY RULE C95– FORALL SX (FORALL SPX– (IF SX.STATUS < 20 AND – SX.S# = SPX.S#– THEN SPX>QTY <=500));

• Oracle

Note required join condition

Database Rules

• How do we execute the following:– For every orderline there must exist an order.– Every customer must place an order.– No salesrep can have more than 200 customers.– Every orderline must contain a valid part.

• When do we execute

Transition Rules

• Applied as go from one state to another

• Employee marries

• CREATE INTEGRITY RULE S12– IF S’.S# = S.S# THEN– S’.STATUS < S.STATUS;