1. Phase 3. Systems Design
Chapter 6 – Data Design

2. Phase Description
Systems Design is the third of five phases in the systems development life cycle (SDLC)
Now you are ready to begin the physical design of the system that will meet the specifications described in the system requirements document
Systems design tasks include data design, user interface design, and system architecture

3. Data Design Concepts
Before constructing an information system, a systems analyst must understand basic design concepts, including data structures and the characteristics of file-oriented and database systems, including Web-based database design

4. Data Design Concepts Data Structures
A framework for organizing and storing data => consists of one/more files/tables
A file or table contains data about people, places or events that interact with the system
File-oriented system
File processing
Database system
Figure 6-3
Figure 6-2

5. Data Design Concepts
File processing
Database system

6. Data Design Concepts Overview of File Processing
Although less common today, file processing can be more efficient and cost less than a DBMS in certain situations – E.g. large volumes of structured data such as process records in a sequence
Figure 6-4

7. Data Design Concepts Overview of File Processing Potential problems
Data redundancy
Data integrity
Rigid data structure

8. Data Design Concepts Overview of File Processing
Uses various types of files
Master file – relatively permanent data about an entity
Table file – reference data (e.g. tax table, rate tables)
Transaction file – day-to-day business records. Input file that updates master file.
Work file/scratch file – temporary file for a single task
Security file – for backup and recovery purposes
History file – for historical or archiving purposes

9. Data Design Concepts Overview of Database Systems
A properly design database system offers a solution to the problems of file processing
A database might serve 5 separate systems in a database environment
Figure 6-5

10. Data Design Concepts Overview of Database Systems
A database management system (DBMS) is a collection of tools, features, and interfaces that enables users to add, update, manage, access, and analyze the contents of a database
The main advantage of a DBMS is that it offers timely, interactive, and flexible data access

11. Data Design Concepts Overview of Database Systems Advantages
Scalability – expandable/modifiable/downsizable
Better support for client/server systems
Economy of scale – efficiency of high-volume processing on larger computers
Flexible data sharing
Enterprise-wide application – database administrator (DBA)

12. Data Design Concepts Overview of Database Systems Advantages
Stronger standards – for data names, formats, documentation, etc
Controlled redundancy
Better security – define authorization procedures
Increased programmer productivity
Data independence

13. DBMS Components Interface
DML – controls DB operations (storing, retrieving, updating, deleting)
Schema – Defines the DB (fields, tables, relationships)
Physical Data Repository
Figure 6-6

14. Web-Based Database Design
Characteristics of Web-Based Design
In a Web-based design, the Internet serves as the front end, or interface for the database management system. Internet technology provides enormous power and flexibility
Web-based systems are popular because they offer ease of access, cost-effectiveness, and worldwide connectivity
Figure 6-8

15. Web-Based Database Design
Connecting a Database to the Web
Database must be connected to the Internet or intranet
Middleware
Macromedia’s ColdFusion
Figure 6-9

16. Data Design Terminology
Definitions
Entity
Table or file
Field
Attribute
Common field
Record
Tuple
Figure 6-11

17. Data Design Terminology
Key Fields
Primary key – unique field or combination of more than one field (Combination key, Composite key, Concatenated key, Multi-valued key)
Candidate key – any field(s) that could be primary key
Nonkey field – not primary or candidate
Foreign key – a field in one table that matches a primary key.
Secondary key – field that can be used to access/retrieve records. Not unique

18. Data Design Terminology
Referential Integrity
Validity checks can help avoid data input errors
In a relational database, referential integrity means that a foreign key value cannot be entered in one table unless it matches an existing primary key in another table
Figure 6-13

19. Data Relationships
A relationship is a logical link between entities based on how they interact
Entity-Relationship Diagrams
One-to-one relationship (1:1)
One-to-many relationship (1:M)
Many-to-many relationship (M:N)

20. Data Relationships Entity-Relationship Diagrams Cardinality
Cardinality notation
Crow’s foot notation
Unified Modeling Language (UML)
Figure 6-14
Figure 6-15
Figure 6-16
Figure 6-17

21. Normalization Normalization Table design
Involves four stages: unnormalized design, first normal form, second normal form, and third normal form
Most business-related databases must be designed in third normal form

22. Normalization Standard Notation Format
Designing tables is easier if you use a standard notation format to show a table’s structure, fields, and primary key
Example: NAME (FIELD 1, FIELD 2, FIELD 3)

23. Normalization Repeating Groups and Unnormalized Design Repeating group
Often occur in manual documents prepared by users
Unnormalized design

24. Normalization
Repeating Groups and Unnormalized Design

25. Normalization First Normal Form
A table is in first normal form (1NF) if it does not contain a repeating group
To convert, you must expand the table’s primary key to include the primary key of the repeating group

26. Normalization Second Normal Form
To understand second normal form (2NF), you must understand the concept of functional dependence
Field X is functionally dependent on field Y if the value of field X depends on the value of field Y
Note: 1NF with a single field primary key is automatically in 2NF

27. Normalization Second Normal Form
A standard process exists for converting a table from 1NF to 2NF
Create and name a separate table for each field in the existing primary key
Create a new table for each possible combination of the original primary key fields
Study the three tables and place each field with its appropriate primary key
Figure 6-21

28. Normalization
Second Normal Form
Figure 6-21

29. Normalization Third Normal Form
3NF design avoids redundancy and data integrity problems that still can exist in 2NF designs
A table design is in third normal form (3NF) if it is in 2NF and if no nonkey field is dependent on another nonkey field
Figure 6-22

30. Normalization Third Normal Form
To convert the table to 3NF, you must remove all fields from the 2NF table that depend on another nonkey field and place them in a new table that uses the nonkey field as a primary key
Figure 6-23
Figure 6-24
Figure 6-25

31. Steps in Database Design
Create the initial ERD
Assign all data elements to entities
Create 3NF designs for all tables, taking care to identify all primary, secondary, and foreign keys
Verify all data dictionary entries
After creating your final ERD and normalized table designs, you can transform them into a database

32. Database Models Hierarchical and Network Databases
In a hierarchical database, data is organized like a family tree or organization chart, with branches representing parent records and child records
A network database resembles a hierarchical design, but provides somewhat more flexibility

33. Database Models Relational Databases
The relational model was introduced during the 1970s and became popular because it was flexible and powerful
Because all the tables are linked, a user can request data that meets specific conditions
New entities and attributes can be added at any time without restructuring the entire database
Figure 6-34
Figure 6-35

34. Database Models Object-Oriented Databases
Many systems developers are using object-oriented database (OODB) design as a natural extension of the object-oriented analysis process
Object data standard
Object Database Management Group (ODMG)
Each object has a unique object identifier
Figure 6-36
Figure 6-37

35. Data Storage Data Warehousing Data warehouse - dimensions
Without a data warehouse it would be difficult for a user to extract data that spans several information systems and time frames
Allows users to retrieve and analyze the data easily
Figure 6-38

36. Data Storage Data Mining
Works best when you have clear, measurable goals
Increase average pages viewed per session.
Increase number of referred customers
Reduce clicks to close
Increase checkouts per visit
Increase average profit per checkout
Figure 6-39

37. Data Storage Logical and Physical Storage Logical storage
As seen through a user’s eyes
Characters
Date element or data item
Logical record
Physical storage
Hardware-related
Physical record or block
Blocking factor
Figure 6-40

38. Data Storage Data Storage Formats Binary digits Bit Byte
EBCDIC and ASCII
Unicode
Figure 6-41

39. Data Storage Data Storage Formats Binary Binary storage format
Integer format
Long integer format
Other binary formats exist for efficient storage of exceedingly long numbers

40. Data Storage Selecting a Data Storage Format
In many cases, a user can select a specific data storage format
For example, when using Microsoft Office, you can store documents, spreadsheets, and databases in Unicode-compatible form by using the font called Arial Unicode MS
Best answer is it depends on the situation

41. Data Storage Date Fields
Most date formats now are based on the model established by the International Organization for Standardization (ISO)
Can be sorted easily and used in comparisons
Absolute date
Best method depends on how the specific date will be printed, displayed or used in a calculation
Figure 6-42

42. Data Control
File and database control must include all measures necessary to ensure that data storage is correct, complete, and secure
A well-designed DBMS must provide built-in control and security features, including subschemas, passwords, encryption, audit trail files, and backup and recovery procedures to maintain data
Figure 6-43

43. Data Control User ID Password Backup Recovery procedures
Audit log files
Audit fields