PCLec08 / 1 8. Integrity This session will be directed at the many and various aspects of...

PCLec08 / 1

8. Integrity8. Integrity

This session will be directed at the many and various

aspects of ‘Integrity’

Integrity processes are included to ensure that the

data in the database, and the information derived from

data is clear, complete and accurate.

And we will have another quick look at ‘Business Rules’ also

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But,before we do …..But,before we do …..

Here is an answer to the puzzle which has been keeping you awake for the past 3 nights.

Source Target Time Progressive

C and D move across(A,B) C,D 2 2

D returns (A,B,D) C 1 3

A and B move across (D) A,B,C 10 13

C returns (C,D) A,B 2 15

C and D move across A,B,C,D 2 17

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IntegrityIntegrity

Components of a Data Model

Structure

Operators

Integrity

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Dangers to DataDangers to Data

A DBMS must protect data from several dangers.

- Accidents( programming errors and miskeying) : these are

integrity issues.

- Malicious Use : A security issue.

- Hardware and Software Failures : these are concurrency and restart issues.

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Definitions of IntegrityDefinitions of Integrity

Data integrity requires the database to be an accurate reflection of the real world

Data should be valid and complete

Integrity issues may have been handled external to the database in the application code and possibly in multiple programs.

Codd (1985) states that integrity constraintsspecific to a particular RDBMS must be definable in SQL and stored in the database dictionary (catalog).

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A DBMS Enforced IntegrityA DBMS Enforced Integrity

Employee Table

Empno, emp_name,Age, SalaryEMPNO NUMBER(6,0) NOT NULL Attempt to add an employee without an EMPNO value

INSERT INTO EMPLOYEE(EMP_NAME,AGE,SALARY)VALUES (‘Smith’,22,35000)

This process is rejected by the DBMS but what would happen if the user entered (35000,’Smith’,22 ) ?

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An Applications Forced IntegrityAn Applications Forced Integrity

A further constraintIF AGE > 16 OR AGE < 99

THEN O-KELSE

REJECT ‘Age Invalid’

This represents a segment of program code.

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Integrity EnforcementIntegrity Enforcement

Integrity enforcement is usually split between the DBMS and the application programs.

Using application programs for integrity assertions has disadvantages.

Programming is more complex

Integrity constraints may be repeated

Change management is difficult

Constraints may contradict

Ad hoc operations may avoid the constraints

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Integrity as a Role of the DBMSIntegrity as a Role of the DBMS

Integrity rules must be considered at design time

Transactions must be monitored for violations

and appropriate actions taken

Rules should be few, without overlap and

should not impact performance too much

(this is not an invitation to exclude rules)

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Classifications of IntegritiesClassifications of Integrities

There are various possible classifications.Date(Vol 2)

- Domain Integrity (attribute based)

- Relational Integrity (table based)

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Codd’s CURED or CRUDECodd’s CURED or CRUDE

Type E - Entity Integrity

Type R - Referential Integrity

Type D - Domain Integrity :A user defined datatype

Type C - Column Integrity:Linked to Domain integrity

Type U - User Defined Integrity

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Data IntegrityData Integrity

Some terms you will encounter:

Entity Integrity

Referential Integrity

Functional Dependency (constraints between determinants

and attributes. For each value of the determinant there is only one value for each of the attributes it determines)

Multivalued Dependency

Join Dependency

Domain Constraints

Cardinality Constraint

User Defined Constraints

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Data IntegrityData Integrity

General Principle: Data compliance with a set of rules

Rules Location: Best embodied in the DBMS

If they are contained in an application, there is the danger of saturating a network and causing degraded performance.

This is particularly so in client / server computing - but are ALL the rules applicable to ALL users ?

CONSTRAINTS: Declarative approach where integrity constraints are ‘declared’ as part of a table specification. ANSI SQL-89 and SQL-92 and SQL-93 standards include specifications for integrity constraints syntax and behaviour

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Domain IntegrityDomain Integrity

A domain is a conceptual pool of values from whichone or more attributes draw their actual values.

Domain age range 0-127

Attribute employee_age 16-65

Two values can only be compared if they come fromthe same domain.

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Primary Key IntegrityPrimary Key Integrity

(based on Oracle)

A primary key has these properties– unique value (no duplicates permitted in table)– not null– multiple keys if required– referenced qualification - foreign key(s)– may be limited to a small range of values (the check

option)– may be limited to a large range of values (the ‘exists’

option)

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Foreign Key PropertiesForeign Key Properties

May be unique ( 1 : 1 relationship)

May be multiple keys

May be limited to a range of values (Domain -as for primary Keys)

May be null (as required)

May be not null (as required)

Will reference a Primary Key (or keys)

May be subject to cascade update, delete, insert

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A Domain DefinitionA Domain Definition

DOMAIN GENDER

– Data Type: Character– Length: 6 bytes– Allowable Values: Male, Female, Null– Storage Format: Uppercase– Operations Allowed:– Inherited Operators: String, Unstring, =– Input Editing: Nil– Extra Functions: Is_ Male, Is_Female,What_Gender

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Timing ConstraintsTiming Constraints

When should an integrity be checked ?TC - Test constraint no later than the end of the

current relational request.

TT - Test at the end of the transaction.(terminal test)

START TRANSACTION UPDATE EMPLOYEE SET SALARY= SALARY*1.1 TC

DELETE FROM EMPLOYEE WHERE SALARY > 1000 END TRANSACTION TT

In Oracle, the integrity check is determined by the commands ‘Update Immediate’ or ‘Update Deferred’There is also a ‘set constraints.. Immediate or deferred’ option

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A Few ExamplesA Few Examples

A transaction is a unit of work

1. Single Table - The transaction affects 1 row only does not alter any domain setting.

2. Single Table - The transaction affects multiple rows and will affect domain settings.

When should the domain integrity breach be reported ?

At the first, second - or at the end of the processes ?

When should the transaction be aborted ?

Should there be a log held of these occurrences/rows ?

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A Few ExamplesA Few Examples

3. Single Table - bulk loading.

Should the load process be stopped at the

detection of the first breach ?

Or should the load row be ‘diverted’ to a log file ?

Should there be a number count of failures ?

Should there be a limit over which the process

should be stopped ?

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Slightly More ComplexSlightly More Complex

1:M 1:M

It is possible that multiple rows in table A, table B and table C will be affected by the transaction

Transaction

A B C

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An Algorithm for Integrity ChecksAn Algorithm for Integrity Checks

Determine constraints that apply to request.

Inspect timing types.

Before the end of the relational request run types TC.

Append types TT to the end of the transaction.

Before the end of transaction run types TT.

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Foreign Key RulesForeign Key Rules

For each foreign key three rules need to be answered:

• Can the foreign key accept nulls ?

• What should happen on an attempt to delete the target of a foreign key reference?

• What should happen on an attempt to update the target of a foreign key reference ? (primary key)

Employee Dept

Empnoe1e2e3

enameredbluebrown

Worksfordeptd1

d2

Deptd1d2d3

DnamePayTaxArt

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Foreign Key RulesForeign Key Rules

When should foreign key rules be checked ?

Dept (Deptno, Dname, Budget)

Emp (Empno, Ename, Salary, WorksforDeptno)

WorksforDeptno References Dept delete cascades, update cascades

Depend (Empno, Dependname, Date-of-birth)

Empno references Emp delete cascades, update cascades

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Foreign Keys and Referencing ActionForeign Keys and Referencing Action

CREATE TABLE SUPPLIER etc. Primary Key (Sno ) CREATE TABLE PART etc. Primary Key( Pno ) CREATE TABLE SUPPLIER_PART(etc. Primary Key (Sno,Pno) Foreign Key (Sno) REFERENCES SUPPLIER (Sno) ON DELETE RESTRICT ON UPDATE CASCADES Foreign Key (Pno)REFERENCES PART (Pno) ON DELETE RESTRICT ON UPDATE CASCADES)

e.g. SUPPLIER (Sno,Sname) PART (Pno,Pname) SUPPLIER-PART (Sno,Pno,Qty)

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The relation each Foreign Key identifies is defined. The foreign key clause also contains other information.

DELETE when the target record of a foreign key reference is detected

Performs the operation -

CASCADE - all matching SUPPLIER-PART records are also deleted.

RESTRICT - the delete is restricted such that there are no matching SUPPLIER-PART records.

SET NULL - the foreign key values are all set to NULL (only if nulls are allowed)

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UPDATE when the Primary Key of the target record of a foreign key is updated.

CASCADE

RESTRICT

SET NULLThese options are similar to delete.

Note that the design decisions embodied in pseudo SQL represent constraint information which reflects the nature or business rules of the organisation being modelled.

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Possible Referential Integrity ProcessesPossible Referential Integrity Processes

1. Limited Insert : If an incoming Foreign Key DOES NOT EXIST as a referenced table Primary Key:

ABORT TRANSACTION - REPORT

2. Limited Update : If an incoming Foreign Key DOES NOT EXIST as a referenced table Primary Key

TERMINATE PROCESS

3. Restricted Delete : If there are referencing FOREIGN KEYS in a referencing table

TERMINATE DELETE PROCESS ON REFERENCED TABLE

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4. Restricted Update : If there are referencing Foreign Keys in a referencing table

INHIBIT UPDATE OPERATION ON THE REFERENCED KEY

5. Cascade Delete : If there are Referenced Keys

INITIATE DELETION OPERATION ON REFERENCED

TABLE BY DELETING ALL REFERENCING ROWS

6. Cascade Update : Commence an UPDATE on the REFERENCED TABLE by UPDATING the Foreign Keys on all Referencing Rows in the Referencing Table(s)

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7. Nullify Delete : Commence a DELETE operation on the REFERENCED table by setting ALL the FOREIGN KEYS on the Referencing Table(s) to NULL (watch Data Types)

8. Nullify Update : Set all of the Foreign Keys of the Referencing Table to NULL. This will invalidate any referencing of the Referenced Key (which must not be

NULL)

9. Default Update : Invalidate references to Updated Referenced Keys by setting all Referencing Table

Foreign Keys to a DEFAULT value

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10. Default Delete : Invalidate references to the deleted Referencing Key Value(s) by setting all Referencing Foreign Key values to a DEFAULT value

11. Warning Delete : Permit the deletion BUT Warn the User of the Unattached Foreign Keys which are now present in the Referencing Table(s)

12. Warning Update : Permit the Update BUT Warn the User of Unattached Foreign Keys which are now present in the Referencing Table(s)

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Some Integrity Schema ExamplesSome Integrity Schema Examples

Create table monash1(

city varchar2(13) not null,

studydate date not null,

noonreading number(4,1),

midnightreading number(4,1),

rainfall number,

unique (city,studydate) );

Creates a table with the candidate key of city,studydate

There may be a number of Unique constraints

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rainfall number,

primary key (city,studydate) );

Creates a table with the Primary Key of city,studydate

and there is only 1 such set of values in the table.

There may be a number of Unique constraints.

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rainfall number,

constraint pk_citystudy primary key (city,studydate) );

Creates a table with the Primary Key key of city,studydate

and names the constraint citystudy in the Constraints table.

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Enable, DisableEnable, Disable

There is a feature in Oracle which permits the

Disabling and Enabling of constraints.

e.g. alter table shipping add primary key (ship_no, container_no)

This identifies the composite primary key as ship_no + container_no, and ensures that no two rows have the same values.

The Disable option defines the constraint but does not enforce it.

The Enable function resets the enforcement of the constraint.

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Enable, DisableEnable, Disable

The formats of the ‘disable’ and ‘enable’ commands are :

disable {{unique(column[,column]…) |

primary key |

Constrains constraint} [cascade] } |

all triggers

enable {{ unique(column[,column]…|

primary key |

[using index [initrans integer]

[maxtrans integer]

[Tablespace tablespace]

[Storage storage]

all triggers

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TriggersTriggers

• Oracle triggers are used to include more processing power to the DBMS function for events which affect a database.

• In the following example a Trigger will be set which ensures that changes to employee records will only take place during business hours on working days ( security ?)

• See if you agree ...

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TriggersTriggers

Create trigger emp_permit_change

before

delete or insert or update

on emp

declare dummy integer;

begin

/* if today is a Saturday or Sunday, then return an error*/

if (to_char(sysdate, ‘dy’) = ‘sat’ or

to_char (sysdate, ‘dy’) = ‘sun’)

then raise_application_error (-20501,

‘May not change employee table during the weekend’);

end if;

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TriggersTriggers• Perhaps we need this as well :-

If (to_char(sysdate, ‘hh24’) < 8

or to_char(sysdate, ‘hh24’) >= 18)

then raise application_error (-20502,

‘May only change employee table during working hours’);

end if;

end;

which raises and interesting point - what happens with flexible time and enterprise bargaining ?

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Business Rules and Data ModellingBusiness Rules and Data Modelling

Business Rules are necessary to ensure that data in a database reflects accurately those conditions which apply to data in the real world environment

The following overheads introduce some additional material on this subject

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Business Rules are at the core of commercial applications

If systems ‘obey’ the Business Rules, then– data will be correct– applications will function– users and management will be happy

Which leads us to– what is a business rule ?– where are they declared ?– where are they enforced ?

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4 Proposed Levels of Business Rules

1. Single attribute (column) format definitions enforced by the database

The ‘payment’ column is an amount interpreted as dollars and cents

The Surname column is a text field expressed in the ASCII character set

The Amount_on_Hand column must never be less than 0

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2. Multiple key column relationships

The ‘Brand Name’ column in the Brand table has a many to one relationship with the Manufacturer Name in the Manufacturer table

The Product foreign key in the Sales table has a many to one relationship to the Product primary key in the Product table

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3. Relationships between Entities

This is declared on the entity-relationship diagram, but is not directly enforced by the database because the relationship is many-to-many

The employee is a sub-type of Person

Supplier supplies the Customer

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4. Complex Business Logic

This relates to Business processes

It may be enforced at data entry time by a complex application such as this :-

“When an insurance policy has been committed but has not yet been approved by the underwriter, the administration date can be NULL, but when the policy has been underwritten, the administration date must be present (NOT NULL) and must be more recent than the agreement date”

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From this it can be stated that :

The core database software manages the first 2 levels only - the single column format definitions and multiple column key relationships

Level 3 (relationships between entities) and Level 4 (complex business logic) should also be enforced as there is much valuable business content at this level (or should that be essential ?)

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Entity relationship modelling (E/R modelling) seems to be a comprehensive language for mapping and describing relationships between entities.

E/R modelling is a diagrammatic technique which specifies

one-to-one

many-to-one and

many-to-many relationships among data elements

It is a logical model

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Computer Associates’ Erwin converts an E/R diagram into data definition language declarations

These declarations define key definitions and join constraints

You can follow this up, and use an Erwin example at

www.cai.com

Gershwin, which you have probably met, is a simpler E/R modelling tool

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E/R modelling is a useful technique for beginning the process of understanding and enforcing business rules

It does not provide a guarantee of completeness

E/R Modelling is incomplete in that the diagrams represent only what the designer decided to stress, or was aware of.

There is no test of an E/R diagram to determine if the designer has specified all possible one-to-one, one-to-many or many-to-many relationships.

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E/R modelling is not unique

A given set of data relationships can be represented by a number of E/R diagrams

Many real data relationships are many-to-many.

The E/R diagram model does not enforce the M:N situations which may involve various conditions and degrees of correlation which would be useful (and perhaps essential) to include a business rules. E/R modelling provides no extensions to the basic many-to-many declaration

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Many E/R models are ideal, not real

Many corporate models are based on ‘how things should be’

This is very useful in understanding the business

BUT if the model must be populated with real data

E/R models are rarely models of real data

There aren’t any tools for trawling over real data data sets and developing E/R models

The E/R model is invariably constructed and the data is ‘fitted’ into the model - and that means we need to clean data before it becomes resident in the model.

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Business Rules and Data modellingBusiness Rules and Data modelling

E/R models lead to complex schemas which mitigate against the objectives of Information Delivery

As an example, the E/R diagram which underpins Oracle Financials (a current Applications Package) requires approximately 2000 tables

SAP’s model can require 10,000 tables.

All of which tends to work against the objectives of easy to understand models, and high performance.

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Chris Date (An Introduction to Database Systems, 7th edition) has this to say :

‘the E/R model is incapable of dealing with integrity constraints or ‘business rules’ except for a few special cases.

Declarative rules are too complex to be captured as part of the business model and must be defined separately by the analyst/developer’.

PCLec08 / 1 8. Integrity This session will be directed at the many and various aspects of...

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