Appendix A
Data Modeling
Data and Process Modeling
Data and Process Modeling
During systems development both processes
During systems development both processes
and data must be modeled
and data must be modeled
–
Data modeling describes data used by system
Data modeling describes data used by system
–
Process modeling describes processes carried out
Process modeling describes processes carried out
by system
by system
Level of detail
Level of detail
Entity-Relationship
Entity-Relationship
Diagram (ERD)
Diagram (ERD)
Documents firm’s data by identifying types
Documents firm’s data by identifying types
of data entities and their interrelationships
of data entities and their interrelationships
Prepared at “big picture” point of data
Prepared at “big picture” point of data
specification
specification
Entity Types
Entity Types
Environmental
Environmental
Resource
Resource
Important transaction
Important transaction
Relationship
Relationship
Relationship symbol
Fills out
Employee Time card
Connectivity
Time card
A. One to one
Produces
Payroll
check
B. One to many
Contains
Invoice
C. Many to many
Customer
Purchases
Product
1
1
1
M
M
M
Inventory
item
Attributes
Attributes
Characteristics of an entity
Characteristics of an entity
Actually data elements
Actually data elements
Preparation of an
Preparation of an
Entity-Relationship Diagram
Relationship Diagram
1. Identify the entities
1. Identify the entities
2. Identify the relationships
2. Identify the relationships
3. Prepare a rough ERD
3. Prepare a rough ERD
4. Map data elements to the entities
4. Map data elements to the entities
5. Perform a data analysis (through third normal
5. Perform a data analysis (through third normal
form is common)
form is common)
6. Prepare a modified ERD
6. Prepare a modified ERD
7. Review the ERD with users and refine
Fills
Purchase order
Supplier
Represents
Accounts payable
Contains Raw
Material Supplier number
Purchase
order number
Supplier number
Item number
1 M M 1
M M
Normalization
Normalization
First normal form (1NF)
First normal form (1NF)
–
Eliminate repeating elements in an entity
Eliminate repeating elements in an entity
Second normal form (2NF)
Second normal form (2NF)
–
Ensure that descriptor attributes rely on the entire
Ensure that descriptor attributes rely on the entire
composite key for the assignment of values
composite key for the assignment of values
Third normal form (3NF)
Third normal form (3NF)
–
Ensure that an attribute value cannot be
Ensure that an attribute value cannot be
determined by values of other attributes
Fills Purchase order Supplier Represents Accounts payable
Contains Raw
Material Supplier number
Supplier name Supplier address
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
Supplier number Supplier name Supplier address
Total accounts payable
Item number Item description
Warehouse location Item unit price
PURCHASE ORDER NUMBER
Purchase order date Supplier number Supplier
Supplier address
Purchase order amount
PURCHASE
ORDER PURCHASEORDER LINE
RAW MATERIAL
CONTAINS REPRESENTS
PURCHASE ORDER NUMBER LINE/ITEM NUMBER
ITEM NUMBER
Item number Item description
Item quantity ordered Item unit price
Item extended price
Item description Warehouse location
Item unit price Balance on hand Recorder point Order quantity Quantity on order
1 M 1 1
Data Dictionary
Data Dictionary
Written description of the data contained in
Written description of the data contained in
the database
the database
First ones maintained in hardcopy form
First ones maintained in hardcopy form
Most are now maintained on a computer
Most are now maintained on a computer
Data flow dictionary entry describes data
Data flow dictionary entry describes data
flows on DFD
Data Dictionary [cont.]
Data Dictionary [cont.]
Data store dictionary entry describes unique
Data store dictionary entry describes unique
data stored in a DFD
data stored in a DFD
Data structure dictionary entry is completed
Data structure dictionary entry is completed
for each structure listed on the data store and
for each structure listed on the data store and
data flow forms
data flow forms
Data element dictionary entry is used for
Data element dictionary entry is used for
each data element, or attribute included in all
each data element, or attribute included in all
of the structures
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
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
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
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: 0001-9999
Typical value:
Summary
Summary
During early years of computing, emphasis
During early years of computing, emphasis
was on the processes performed.
was on the processes performed.
Currently, emphasis is on data
Currently, emphasis is on data
ERDs are a primary tool in data analysis
ERDs are a primary tool in data analysis
Data dictionaries provide a means of
Data dictionaries provide a means of
