1. DATABASE APPLICATION DEVELOPMENT SAK 3408
Database Design I
(week 2)

2. REMEMBER Best: Spend your time on design and SQL. Worst:
Program
Best:
Spend your time
on design and SQL.
Design
SQL
Program
Worst:
Compensate for poor design
and limited SQL with programming.
SAK3408 by PSS (W2)

3. Database System Design
User views
of data.
Conceptual
data model.
Implementation
(relational)
data model.
Physical
data
storage.
Class diagram that shows business entities, relationships, and rules.
List of nicely-behaved tables. Use data normalization to derive the list.
Indexes and storage methods to improve performance.
SAK3408 by PSS (W2)

4. The Need for Design
Goal: To produce an information system that adds value for the user
Reduce costs
Increase sales/revenue
Provide competitive advantage
Objective: To understand the system
To improve it
To communicate with users and IT staff
Methodology: Build models of the system
SAK3408 by PSS (W2)

5. Designing Systems Designs are a model of existing & proposed systems
They provide a picture or representation of reality
They are a simplification
Someone should be able to read your design (model) and describe the features of the actual system.
SAK3408 by PSS (W2)

6. How to builds your model?
You build models by talking with the users
Identify processes
Identify objects
Determine current problems and future needs
Collect user documents (views)
Break complex systems into pieces and levels
SAK3408 by PSS (W2)

7. Initial Steps of Design
1. Identify the exact goals of the system.
2. Talk with the users to identify the basic forms and reports.
3. Identify the data items to be stored.
4. Design the classes (tables) and relationships.
5. Identify any business constraints.
6. Verify the design matches the business rules.
SAK3408 by PSS (W2)

8. Design Stages Physical Design Initiation Table definitions Scope
Application development
Queries
Forms
Reports
Application integration
Data storage
Security
Procedures
Implementation
Training
Purchases
Data conversion
Installation
Evaluation & Review
Initiation
Scope
Feasibility
Cost & Time estimates
Requirements Analysis
User Views & Needs
Forms
Reports
Processes & Events
Objects & Attributes
Conceptual Design
Models
Data flow diagram
Entity Relationships
Objects
User feedback
SAK3408 by PSS (W2)

9. Overview of Database Design Process
REQUIREMENTS COLLECTION & ANALYSIS
Functional Requirements
Data requirement
FUNCTIONAL ANALYSIS
CONCEPTUAL DESIGN
High-Level Transaction Specification
Conceptual Schema
DBMS-independent
DBMS-specific
LOGICAL DESIGN
(DATA MODEL MAPPING)
APPLICATION PROGRAM DESIGN
Logical Schema
In the data model of specific DBMS
TRANSACTION IMPLEMENTATION
PHYSICAL DESIGN
Application Program
Internal Schema
SAK3408 by PSS (W2)

10. Unified Modeling Language (UML)
A relatively new method to design systems.
Contains several types of diagrams:
Contains several types of diagrams:
The class diagram is the most important for database design.
SAK3408 by PSS (W2)

11. Definitions
Entity: Something in the real world that we wish to describe or track.
Class: Description of an entity, that includes its attributes (properties) and behavior (methods).
Object: One instance of a class with specific data.
Property: A characteristic or descriptor of a class or entity.
Method: A function that is performed by the class.
Association: A relationship between two or more classes.
Pet Store Examples
Entity: Customer, Merchandise, Sales
Class: Customer, Merchandise, Sale
Object: Joe Jones, Premium Cat Food, Sale #32
Property: LastName, Description, SaleDate
Method: AddCustomer, UpdateInventory, ComputeTotal
Association: Each Sale can have only one Customer.
SAK3408 by PSS (W2)

12. Business Rule
BR are important in data modelling because they govern how data are – handled and stored.
Basic BR :
Data names
Data definition
Names and definition must provide for :
Entity types
Attribute
Relationship
SAK3408 by PSS (W2)

13. Guideline Data Names Relate to business – customer \ File10
Be meaningful – avoid is, it, has
Be unique – homeadd, campusadd
Repeatable–studbirthdate, stafbirthdate
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14. Data Definition
“ A course is a module of instruction in a particular area.”
“A customer may request a model car from a rental branch in a particular date.”
Guideline :
A definition will state such characteristics of the data objects.
Whether the data is singular or plural
Who determine the value for the data
Whether data is static or changes over time
Whether the data is optional or an empty
Where, when and how data is created.
SAK3408 by PSS (W2)

15. The E-R Model
E-R model – a logical representation of the data for an organization or for a business area
E-R diagram – a graphical representation of an entity-relationship model
SAK3408 by PSS (W2)

16. E-R Model Constructs
Entity
Attribute
Relationship
SAK3408 by PSS (W2)

17. Basic E-R Notation A special entity that is also a relationship
Entity symbols
Attribute symbols
Relationship symbols
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18. Figure 2.3 Sample E-R Diagram
SAK3408 by PSS (W2)

19. Entity
An entity is a person, place, object, event or concept in the user environment about which the organization wishes to maintain data.
Ex:
Person – EMPLOYEE, STUDENT, PATIENT
Place – STORE, WAREHOUSE, STATE
Object – MACHINE, BUILDING, AUTOMOBILE
Event – SALE, REGISTRATION, RENEWAL
Concept – ACCOUNT, COURSE
Entity type, entity instances, strong entity, weak entity
SAK3408 by PSS (W2)

20. Entity Type vs. Entity Instance
Share common characteristic
Given a name (CAPITAL LETTER)
Rectangle
Collection of entities (often corresponds to a table). Ex: EMPLOYEE
Entity Instances
a single occurrence of an entity type (often corresponds to a row in a table)
Ex: may be 100 of instances of entity EMPLOYEE stored in database.
SAK3408 by PSS (W2)

21. Entity Type vs. Entity Instance (cont.)
Entity Type : EMPLOYEE
Attribut : EMP_NUM CHAR(10)
NAME CHAR(25)
STATE CHAR(35)
2 instances of EMPLOYEE :
Ali Amir
Perak Kedah
SAK3408 by PSS (W2)

22. Strong vs. Weak Entity Types
Strong Entity Type
entity that exists independently of other entity types
Unique characteristic
Called an identifier
Ex: STUDENT, EMPLOYEE
Weak Entity Type
entity type whose existence depends on some other entity type
No meaning in ERD without strong entity.
SAK3408 by PSS (W2)

23. Figure 2.10 Strong and weak entities
Identifying relationship
Strong entity
Weak entity
SAK3408 by PSS (W2)

24. Attribute
property or characteristic of an entity type (often corresponds to a field in a table)
Ex:
entity type – STUDENT
Attributes – name, add, id, program
Simple att vs composite att.
Single-valued att vs multivalued att
Stored att vs derived att
Identifier att.
SAK3408 by PSS (W2)

25. Example
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26. Simple vs. Composite Attribute
Simple attribute – cannot broken into smaller components
Composite attribute – can broken into component parts
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27. Simple key attribute
The key is underlined
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28. a) Composite attribute
An attribute broken into component parts
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29. b) Composite key attribute
The key is composed
of two subparts
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30. Single-Valued vs. Multivalued Attribute
Single-Valued – each of the attributes has one value
Multivalued – attribute more than one value
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31. Entity with a multivalued attribute (Skill)
an employee can have
more than one skill
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32. Stored vs. Derived Attributes
Stored attribute – data input or set
Derived Attribute – attribute whose values can be calculated from related attribute values.
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33. Entity with a derived attribute (Years_Employed)
from date employed and current date
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34. Identifiers (Keys)
Identifier (Primary Key) - An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Composite Identifier – an identifier that consists of a composite attribute.
Candidate Key – an attribute that could be a key…satisfies the requirements for being a key
SAK3408 by PSS (W2)

35. Characteristics of Identifiers
Will not change in value
Will not be null
No intelligent identifiers (e.g. containing locations or people that might change)
Substitute new, simple keys for long, composite keys
SAK3408 by PSS (W2)

36. Ex: identifier
The key is composed
of two subparts
SAK3408 by PSS (W2)

37. Relationship Relationship
link between entities (corresponds to primary key-foreign key equivalencies in related tables)
Relationship Types vs. Relationship Instances
The relationship type is modeled as the diamond and lines between entity types…the instance is between specific entity instances
SAK3408 by PSS (W2)

38. Relationships (cont.) Relationship Types vs. Relationship Instances
The relationship type is modeled as the diamond and lines between entity types…the instance is between specific entity instances
SAK3408 by PSS (W2)

39. Figure 2.6 (a) Relationship type
Figure 2.6 (b) Entity and Relationship instances
SAK3408 by PSS (W2)

40. Relationships (cont.) Relationships can have attributes
These describe features pertaining to the association between the entities in the relationship
Two entities can have more than one type of relationship between them (multiple relationships)
Associative Entity = combination of relationship and entity
SAK3408 by PSS (W2)

41. Degree of Relationships
Degree of a Relationship is the number of entity types that participate in it
Unary Relationship
Binary Relationship
Ternary Relationship
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42. Figure 2.7 Degree of relationships
Entities of two different types related to each other
One entity related to another of the same entity type
Entities of three different types related to each other
SAK3408 by PSS (W2)

43. Cardinality of Relationships
One – to – One
Each entity in the relationship will have exactly one related entity
One – to – Many
An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity
Many – to – Many
Entities on both sides of the relationship can have many related entities on the other side
SAK3408 by PSS (W2)

44. Figure 2.8 Degree of relationships and Cardinality
(a) Unary relationships
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45. (b) Binary relationships
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46. (c) Ternary relationships
Note: a relationship can have attributes of its own
SAK3408 by PSS (W2)

47. Cardinality Constraints
Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.
Minimum Cardinality
If zero, then optional
If one or more, then mandatory
Maximum Cardinality
The maximum number
SAK3408 by PSS (W2) 29

48. Figure 2.8 Cardinality Mandatory and Optional
SAK3408 by PSS (W2) 8

49. Figure 2.9 Cardinality Constraints
(a) Basic relationship with only maximum cardinalities showing
(b) Mandatory minimum cardinalities
SAK3408 by PSS (W2)

50. Figure 2.10 Examples of multiple relationships
Employees and departments – entities can be related to one another in more than one way
SAK3408 by PSS (W2)

51. SAK3408 by PSS (W2)

52. Strong vs. Weak Entities, and Identifying Relationships
Strong entities
exist independently of other types of entities
has its own unique identifier
represented with single-line rectangle
Weak entity
dependent on a strong entity…cannot exist on its own
Does not have a unique identifier
represented with double-line rectangle
Identifying relationship
links strong entities to weak entities
represented with double line diamond
SAK3408 by PSS (W2)

53. Associative Entities It’s an entity – it has attributes
AND it’s a relationship – it links entities together
When should a relationship with attributes instead be an associative entity?
All relationships for the associative entity should be many
The associative entity could have meaning independent of the other entities
The associative entity preferably has a unique identifier, and should also have other attributes
The associative may be participating in other relationships other than the entities of the associated relationship
Ternary relationships should be converted to associative entities
SAK3408 by PSS (W2)

54. Figure 2.11 An associative entity
(a) An associative entity (CERTIFICATE)
Associative entity involves a rectangle with a diamond inside.
Note that the many-to-many cardinality symbols face toward the associative entity and not toward the other entities
SAK3408 by PSS (W2) 21

55. (b)Ternary relationship as an associative entity
SAK3408 by PSS (W2) 36

56. Components of E-R Model
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57. Recalled : Teaching Plan W2
Database design stages
Conceptual data model
Unified Modeling Language
Entity Relationship Diagram (ERD)
SAK3408 by PSS (W2)