1. Appendix A Data Modeling MANAGEMENT INFORMATION SYSTEMS 8/E
Raymond McLeod, Jr. and George Schell
Appendix A
Data Modeling
A-1
Copyright 2001 Prentice-Hall, Inc. 1

2. Data and Process Modeling
During systems development both processes and data must be modeled
Data modeling describes data used by system
Process modeling describes processes carried out by system
Level of detail
Varies between highest summary and lowest detail
Structured tools enable level of detail to be varied
A-2

3. Entity-Relationship Diagram (ERD)
Documents firm’s data by identifying types of data entities and their interrelationships
Prepared at “big picture” point of data specification
Very flexible
A-3

4. Entity Types Environmental Resource Important transaction Entity
symbol
A-4

5. An association between two entity types
Relationship
An association between two entity types
Relationship
symbol
Time card
Employee
Fills out
A-5

6. Number of times an entity occurs in relation to another entity
Connectivity
Number of times an entity occurs in relation to another entity 1 1
Payroll
check
Time card
Produces
A. One to one 1 M
Inventory
item
Invoice
Contains
B. One to many M M
Customer
Purchases
Product
C. Many to many
A-6 3

7. Attributes Characteristics of an entity Actually data elements
Identifiers are unique attributes of the entity
Descriptors describe the entity
A-7

8. Preparation of an Entity-Relationship Diagram
1. Identify the entities
2. Identify the relationships
3. Prepare a rough ERD
4. Map data elements to the entities
5. Perform a data analysis (through third normal form is common)
6. Prepare a modified ERD
7. Review the ERD with users and refine
A-8

9. Rough ERD Supplier number 1 Fills M Purchase order number M M Raw
Material
Contains M
Represents
Item number 1
Accounts
payable
Supplier number
A-9 4

10. Normalization First normal form (1NF) Second normal form (2NF)
Eliminate repeating elements in an entity
Second normal form (2NF)
Ensure that descriptor attributes rely on the entire composite key for the assignment of values
Third normal form (3NF)
Ensure that an attribute value cannot be determined by values of other attributes
A-10

11. Data Elements are Mapped Supplier number Supplier name
Supplier address
Supplier
Data Elements
are Mapped 1
Purchase order number
Purchase order date
Supplier number
Supplier name
Supplier address
Item number (n times)
Item description (n times)
Item quantity (n times)
Item unit price (n times)
Item extended price (n time)
Purchase order amount
Fills M M M
Purchase
order
Raw
Material
Contains M
Item number
Item description
Warehouse location
Item unit price
Balance on hand
Reorder point
Order quantity
Quantity on hand
Represents
Supplier number
Supplier name
Supplier address
Total accounts payable 1
Accounts
payable
A-11 4

12. Normalized Portion of ERD
PURCHASE
ORDER 1 M
PURCHASE
ORDER
LINE 1 1
RAW
MATERIAL
CONTAINS
REPRESENTS
PURCHASE ORDER NUMBER LINE/ITEM NUMBER
PURCHASE ORDER
NUMBER
Purchase order date
Supplier number
Supplier
Supplier address
Purchase order amount
ITEM NUMBER
Item description
Warehouse location
Item unit price
Balance on hand
Recorder point
Order quantity
Quantity on order
Item number
Item description
Item quantity ordered
Item unit price
Item extended price
A-12 6

13. Data Dictionary
Written description of the data contained in the database
First ones maintained in hardcopy form
Most are now maintained on a computer
Data flow dictionary entry describes data flows on DFD
A-13

14. Data Dictionary [cont.]
Data store dictionary entry describes unique data stored in a DFD
Data structure dictionary entry is completed for each structure listed on the data store and data flow forms
Data element dictionary entry is used for each data element, or attribute included in all of the structures
A-14

15. Data Flow Dictionary Entry
Data flow name: Sales Order
Description: The documents that are filled out by customers to identify the products, and the quantities of each, that they will wish to purchase.
From: 1. Open mail
To: 2. Enter sales order information
Data structures: Sales order record
Comments:
A-15

16. Data Store Dictionary Entry
Data store name: Sales order form
Description: The history file of sales order forms, after the data has been entered into the sales commission system.
Data structures: Sales order record
Volume: Approximately 140 per day
Activity:
Access: Order department personnel
Comments:
A-16

17. Data Structure Dictionary Entry
Structure name: Sales order record
Description: The sales order form that the customer uses to order merchandise.
Date elements: Customer.Number
Customer.Order.Number
Salesperson.Number
Customer.Order.Date
*Item.Number
*Item.Description
*Item.Quantity
*Item.Unit.Price
*Item.Extended.Price
Comments: Elements marked with asterisks occur for each item record
A-17

18. Data Element Dictionary Entry
Data element name: Salesperson.Number
Description: The number that identifies the salesperson
Type: Numeric
Length: 4
No. decimal pos.
Aliases: Salesman number, Sales rep number
Range of values:
Typical value:
Specific values:
Other editing details:
A-18

19. Summary
During early years of computing, emphasis was on the processes performed.
Currently, emphasis is on data
ERDs are a primary tool in data analysis
Data dictionaries provide a means of documenting data
A-19