Transcript Appendix B - IST Akprind Yogyakarta

PEMODELAN SISTEM
 Process Modeling
 Data Modeling
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
Process
Modelling
Copyright 2001 Prentice-Hall, Inc.
Data Flow Diagrams (DFDs)
 Graphic representation of a system
that uses a small number of symbol
shapes to illustrate how data flows
through interconnected processes
 Most natural way to document processes
 Emphasis on processes rather than data
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DFD Symbols
 DFDs consist of four symbols
1) Environmental elements called
terminators
 Person
 Organization
 Another system
2) Processes which transform inputs to
outputs
 Labeled with verb and object
 Also labeled with system or computer
program name
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DFD Symbols [cont.]
 DFD symbols [cont.]
 Data flows which consist of logically
related data elements that travel from
one point or process to another. In other
words, data in motion.
 Structures
 Diverge
 Converge
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DFD Symbols [cont.]
 DFD symbols [cont.]
 Data stores which are data repositories.
In other words, data at rest.
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Mail
Customer
1.
Open
mail
Entered
sales order
data
3.
Sort
sales
order s
A Data Flow Diagram (Figure 0
Diagram) of a Sales Commission
System
Sales
orders
2.
Enter sales
order data
Entered
sales orders
Sales order
form file
Sorted
sales
records
4.
Compute
sales
commissions
Sales commission
report
Sales
manager
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When Drawing a Context Diagram
1. Use only a single process symbol
2. Label the process symbol to
represent the entire system
3. Do not number the single process
symbol
4. Include all terminators for the system
5. Show all the data flows between the
terminators and the system
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Mail
Customer
A Context Diagram of a
Sales Commission System
Sales
Commission
System
Sales
commission
report
Sales
Manager
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Figure n Diagrams
 Documents a single process of a DFD
in a greater amount of detail
 n represents the number of the
process on the next higher level that
is being documented
 The term “leveled DFDs” describe the
hierarchy of diagrams ranging from
context to the lowest-level figure n
diagram
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Figure 4 Diagram of a Sales Commission System
3
Sorted
sales
records
4.1
Compute
commission
amounts
Sales
commission
report
4.2
Accumulate
totals
Sales
manager
Commission
amounts
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How Many Levels to Use?
 Restrict a single DFD to no more than
six to eight processes
 Use another tool to document the
lowest level of detail but use no more
than a single page.
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Data Flow Diagramming Guidelines
1. Label each data flow with a unique name.
2. Keep data flow names constant between levels.
3. Show proper disposition of records deleted from a data
store.
4. When documenting a computer program, do not
include reads/writes.
5. Avoid read-only processes.
6. Write-only processes are permissible when time serves
as the trigger.
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Structured English
 Narrative form of computer code
documentation
 Based on Pseudocode
 Abbreviated, formalized pseudocode
in a particular format that looks like
computer code
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Structured English Guidelines
 1) Use a verb when describing each
processing strip.
 2) Supplement verb with one or
more objects when necessary.
 3) Use only three constructs of
programming.
 Sequence
 Selection
 Repetition
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Structured English
Guidelines [cont.]
 4) Use only data names defined in
the data dictionary.
 5) Use uppercase for all data names
and computer syntax.
 6) Indent to show a hierarchical
structure.
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Structured English
Guidelines [cont.]
 7) When documentation is
subdivided into modules, use the
first line of each module for an
identifying label and leave at least
one blank line in-between.
 8) Restrict each module to a single
entry and exit point.
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Structure English Example
START
Initialize storage
TOTAL.SALES, TOT.COM = 0
Process sales data
DO WHILE (more records)
PERFORM READ DATA
PERFORM PROCESS DATA
PERFORM PRINT DATA
END DO
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Summary
 Process modeling is an important
part of system design
 Various techniques exist for process
modeling
 DFDs
 Structured English
 Manager can use Structured English
and DFDs to communicate system
requirements
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Data Modelling
Copyright 2001 Prentice-Hall, Inc.
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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
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Entity Types
 Environmental
 Resource
 Important transaction
Entity
symbol
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Relationship
An association between two entity types
Relationship
symbol
Employee
Fills out
Time card
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Connectivity
Time card
1
Number of times an entity occurs
in relation to another entity
Produces
1
Payroll
check
A. One to one
Dosen
1
Sebagai dosen M Mahasiswa
wali
M
M
B. One to many
Mahasiswa
Mengambil
Matakuliah
C. Many to many
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Attributes
 Characteristics of an entity
 Actually data elements
 Identifiers are unique attributes of
the entity
 Descriptors describe the entity
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Preparation of an Entity-Relationship
Diagram
1.
2.
3.
4.
5.
Identify the entities
Identify the relationships
Prepare a rough ERD
Map data elements to the entities
Perform a data analysis (through third
normal form is common)
6. Prepare a modified ERD
7. Review the ERD with users and refine
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Rough ERD
Supplier
Supplier number
1
Fills
M
Purchase
order number
Purchase
order
M
Contains
M
Raw
Material
M
Represents
Item number
1
Supplier number
Accounts
payable
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Normalization
 First normal form (1NF)
 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
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Supplier number
Supplier name
Supplier address
1
Purchase order number
Purchase order date
Fills
Supplier number
Supplier name
M
Supplier address
Item number (n times)
Purchase
Item description (n times)
order
Item quantity (n times)
Item unit price (n times)
M
Item extended price (n time)
Purchase order amount
Represents
Supplier number
Supplier name
Supplier address
Total accounts payable
Data Elements
are Mapped
Supplier
1
Accounts
payable
M
Contains
M
Raw
Material
Item number
Item description
Warehouse location
Item unit price
Balance on hand
Reorder point
Order quantity
Quantity on hand
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Normalized Portion of ERD
PURCHASE
ORDER
1
M
CONTAINS
PURCHASE ORDER
NUMBER
Purchase order date
Supplier number
Supplier
Supplier address
Purchase order amount
PURCHASE
ORDER
LINE
1
1
REPRESENTS
PURCHASE ORDER NUMBER
ITEM NUMBER
Item number
Item description
Item quantity ordered
Item unit price
Item extended price
RAW
MATERIAL
LINE/ITEM NUMBER
Item description
Warehouse
location
Item unit price
Balance on hand
Recorder point
Order quantity
Quantity on order
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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
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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
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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:
information
2. Enter sales order
Data structures:
Sales order record
Comments:
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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:
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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
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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:
Specific values:
Other editing details:
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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
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