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07/16/96
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2. Relational Model

3. Topics Database Models Keys Relational Integrity Business Rule
Hierarchical Model
Network Model
Relational Model
Entity Relationship Model
Object Oriented Model
Keys
Primary Keys
Foreign Keys
Relational Integrity
Business Rule

4. Database Models
A way of thinking about data in a database is called a logical database model (or implementation model).
Types of Logical Model
Hierarchical Model
Network Model
Relational Model
Entity Relationship Model
Object Oriented Model

5. Database Models

6. Hierarchical Model Developed in the 1960s
To manage large amounts of data for complex manufacturing projects such as Apollo rocket that landed on moon (1969)
Its basic logical structure is represented by an upside-down tree.
The hierarchical structure contains levels, or segments. A segment is equivalent of a file system’s record type.

7. Hierarchical Model
Within the hierarchy, a higher layer is perceived as the parent of the segment directly beneath it, which is called the child.
The hierarchical model depicts a set of one-to-many (1:M) relationships between a parent and its children segments.
Each parent can have many children, but each child has only one parent.

8. Hierarchical Model

9. Hierarchical Model

10. Hierarchical Model
Hierarchical views can differ between user group

11. Network Model
Network Model was created to represent complex data relationships more effectively than hierarchical model, to improve database performance, and to impose a database standard.
User perceives the network database as a collection of records in 1:M relationships.
Unlike the Hierarchical Model, Network Model allows a record to have more than one parent.

12. Network Model Some important concepts are:
Schema, which is the conceptual organization of entire database as viewed by database administrator.
Subschema, which defines portion of database “seen” by application programs that actually produce desired information from data contained within the database.

13. Network Model
Data Manipulation Language (DML), which defines environment in which data can be managed and to work with data in database.
A schema Data Definition Language (DDL), which enables the database administrator to define the schema components.

14. Network Model

15. Network Model

16. Relational Model
Relational Model was introduced in 1970 by E. F. Codd (of IBM) in his landmark paper “A Relational Model of Data for Large Shared Databanks”
Data model that represents data in form of tables or relation.

17. Relational Model
Relational database model consists of following three components:
Data structure: Data are organized in form of tables or relations.
Data manipulation: Powerful operations such as SQL languages or Query-by-example, are used to manipulate data stored in database.
Data integrity: Business rules are specified to maintain integrity of data when they are manipulated.

18. Relational Model Physical Properties
A relation consists of 1 or more columns and 0 or more rows.
A row is called a tuple.
Each relation is given a unique name.
Each column has a name unique within the relation.
Each row contains an instance of the data associated with the relation.
A relation with no rows is empty (contains no data), but still exists.

19. Relational Model Logical Properties
Columns are unordered, left to right. This property is designed to preserve the independence of each column.
Rows are unordered, top to bottom. This is designed to preserve the independence of each row.
No row may be duplicated in a given relation. Uniqueness in a relation is guaranteed by the designation of a Primary Key for each relation.

20. Relational Model
A Candidate Key is an attribute that uniquely identifies a row in that relation.
A Primary Key is a candidate key that has been selected to be unique identifier for each row.
Primary key values cannot be null, since they would then not identify a row.
Columns can be interchanged without changing the meaning or use of relation.
It makes no difference as whether to insert a new row in front or at end of table.

21. Relational Model

22. Entity Relationship Model
Peter Chen first introduced the ER data model in 1976
Graphical representation of entities and their relationships in database structure.
ER Models are normally represented in an Entity Relationship Diagram (ERD) to model database components.
It complemented Relational Data model.
Relational Data Model and ERM combined to provide foundation for structured database design.

23. Entity Relationship Model

24. Object Oriented Model
Object-Oriented Data Model (OODM), both data and their relationships are contained in a single structure known as an object
OODM reflects a very different way to define and use entities. Object is described by its factual content. Object includes information about relationships between the facts within the object, as well as information about its relationships with other objects.

25. Object Oriented Model Facts within object are given greater meaning.
OODM is said to be a Semantic Data Model because semantic indicates meaning.
OODM is the basis for Object-Oriented Database Management System (OODBMS).

26. Object Oriented Model

27. Database Models Earlier Models Relational Model
Difficult to change structure
Unplanned queries difficult to support
Have to ‘navigate’ through the database
Data stored in linked sets physically
Programmer must be aware of structure
Relational Model
Easy to understand concepts
Logical/Physical aspects clearly separated
No (visible) physical pointers used
Easy to set-up and change
Set-oriented (not record-oriented)

28. Keys Choice of Primary Key is an important design issue
Eg. An attribute list for a PERSON entity
Surname
Firstname
DOB
Gender
Passport number
Driving Licence number
Election number
Citizenship number

29. Primary Keys
PRIMARY KEY for a table T1 is a column PK of T1 such that, at any given time, no two rows of T1 have same value for PK.
An entity’s primary key is one or more of its attributes which together uniquely identify an occurrence of the entity.

30. Primary Keys STUDENT (Student-ID, Student-Name, Address) STUDENT
Tom
12a Clover Street
S1002
Alex
Flat B High Street
S1003
Brown
218 Tulip Road

31. Primary Keys
FEATURES
Can never take on a particular set of values in more than one occurrence of the entity.
No primary key attribute can have a null value.
Every attribute in the primary key is mandatory.

32. Foreign Key
FOREIGN KEY is a column FK of some table T2 such that, at any given time, every (non NULL) value of FK in T2 is required to be equal to the value of the PRIMARY KEY PK in some row of some base table T1.
Foreign keys are the ‘glue’ that holds the database together and rrepresents certain relationships between tuples.
CUSTOMER
ORDER-LINE
ORDER
places
comprised of

33. Foreign Key LECTURER-LOCATION(Department*, Location
LECTURER(Lecture-Id, Lecture-Name, Department, Salary)
Lecturer-id
Lecturer-name
Department
Salary
W01
Emma Greg
Computing
35,000
S01
Wendy Holder
42,000
D01
Amy King
Accounting
27,000
J02
Bob Jones
29,000
N01
Bob Whales
36,500
J01
Jack Nelson
History
41,500
Department
Location
Computing
Moorgate
Accounting
Staples
History
Lewiston
LECTURER-LOCATION(Department*, Location

34. Foreign Key CUSTOMER ORDER ORDER-LINE Cust-id Cust-name Credit-Status
Business-type
1001
Smith
Excellent
Retail
1910
Jones
Good
Wholesale
2450
Brown
Fair
Multiple
ORDER
Order-no
Date
Cust-id*
100
01/02/06
1910
101
04/06/06
1001
102
15/06/06
ORDER-LINE
Order-no*
Item-no
Item-name
Quality
100 11
Spade 15 92
Shovel 10
101 12
102 50

35. Foreign Key Feature: Feature:
There is no requirement that a Foreign Key be a component of the Primary Key.
DEPARTMENT
Dept-code ……
EMPLOYEE
Empl-no ……
Dept-code*
Feature:
A foreign key will be composite if the primary key it matches is composite.
VEHICLE
Manufacturer-name
Model-name ……
VEHICLE-IN-STOCK
Vehicle-no
Manufacturer-name*
Model-name* …

36. Foreign Key
Feature:
Many-To-Many relationships are always decomposed with Foreign keys making up a composite Primary Key.
SUPPLIER
Supp-no ……
PART
Part-no ……
SUPPLY
Supp-no*
Part-no* ……

37. Foreign Key Feature: Note that T1 and T2 do not have to be distinct
EMPLOYEE
Empl-no ……
Mgr-no*

38. Foreign Key
Feature:
There is no requirement that a given Primary Key value must appear in a corresponding Foreign Key.
CUSTOMER
Cust-id
Cust-name
Credit-Status
Business-type
1001
Smith
Excellent
Retail
1910
Jones
Good
Wholesale
2450
Brown
Fair
Multiple
ORDER
Order-no
Date
Cust-id*
100
01/02/06
1910
101
04/06/06
1001
102
15/06/06

39. Domains
The range of values that the entries in a particular column can take is known as the domain.
Example:
The domain of gender has only two values (e.g. Male/Female).
The domain of start date could be any valid date greater than 01/01/2006.
The domain of salary may be restricted to the range 20, ,000.

40. Relational Integrity
Integrity in a database is concerned with the database having correct and consistent data.
Domain Integrity Rule
Every attribute is required to satisfy the constraint that its values are drawn from the relevant domain.
Entity Integrity Rule
No component of the primary key of a base relation is allowed to accept nulls.

41. Relational Integrity Referential Integrity Rule
The database must not contain any unmatched foreign key values.
User-Defined or Application-Specific Integrity

42. Referential Integrity
If a foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null.
CUSTOMER
ORDER
places

43. Referential Integrity
CUSTOMER(Cust-id, Cust-name, Credit-status, Business-type
Cust-id
Cust-name
Credit-Status
Business-type
1001
Smith
Excellent
Retail
1910
Jones
Good
Wholesale
2450
Brown
Fair
Multiple
ORDER(Order-no, Date, Cust-id*)
Order-no
Date
Cust-id*
100
01/02/06
1910
101
04/06/06
1001
102
15/06/06

44. Referential Integrity
For Deletion and Update
RESTRICTED
Operation is ‘restricted’ to the case where no such matching occurs. i.e. attempt to delete (update) customer id 1001 fails.
CASCADES
Operation cascades to delete matches as well. i.e. delete (update) customer id 1001 and orders 101.

45. Referential Integrity
For Deletion and Update
NULLIFIES
Foreign key is set to null in all matches and record is deleted (updated). i.e. delete (update) record, set cust-id in orders 101 to null.

46. Business Rules
Brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization’s environment
Apply to any organization that stores and uses data to generate information
Description of operations that help to create and enforce actions within that organization’s environment

47. Business Rules Must be rendered in writing Must be kept up to date
Sometimes are external to organization
Must be easy to understand and widely disseminated
Describe characteristics of the data as viewed by company

48. Sources of Business Rules
Company Managers
Policy Makers
Department Managers
Written Documentation
Procedures
Standards
Operations manuals
Direct interviews with end users

49. Importance of Business Rules
Promote creation of accurate data model
Standardize company’s view of data
Constitute a communications tool between users and designers
Allow designer to understand nature, role, and scope of data
Allow designer to understand business processes
Allow designer to develop appropriate relationship participation rules and constraints

50. Any Questions?