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Systems Analysis Data and process analysis
ผูส้ อน ดร.สลิล บุญพราหมณ์ ITM-631 Information System Development
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... ความคิดนัน เป็ นแม่บทใหญ่ของการพูดและการกระทํา เพราะกิจทีจ " ะทําคําที" จะพูดทุกอย่างล ้วนสําเร็จมาจากความคิด การคิดก่อนพูดและก่อนทํา จึงชว่ ยให ้บุคคลสามารถยับยัง คําพูดทีไ" ม่สมควร หยุดยัง การกระทําทีไ" ม่ถก ู ต ้อง ... พระบรมราโชวาทของพระบาทสมเด็จพระเจ้าอยูหั ่ ว ในพิธพ ี ระราชทานปริญญาบัตรของจุฬาลงกรณมหาวิ ทยาลัย ์ ๑๐ กรกฎาคม ๒๕๔๐
Chapter Objectives 3
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Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptions
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Describe the symbols used in data flow diagrams and explain the rules for their use
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Draw data flow diagrams in a sequence, from general to specific
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Explain how to level and balance a set of data flow diagrams
Chapter Objectives 4
Describe how a data dictionary is used and what it contains Use process description tools, including structured English, decision tables, and decision trees
Describe the relationship between logical and physical models
Introduction 5
In Chapters 5 & 6, you will develop a logical model of the proposed system and document the system requirements
Logical model shows what the system must do
Physical model describes how the system will be constructed
Overview of Data and Process Modeling Tools 6
Systems analysts use many graphical techniques to describe an information system
A data flow diagram (DFD) uses various symbols to show how the system transforms input data into useful information
Data Flow Diagrams 7
A data flow diagram (DFD)
shows how data moves through an information system but does not show program logic or processing steps A set of DFDs provides a logical model that shows what the system does, not how it does it
Data Flow Diagrams 8
DFD Symbols
Data Flow Diagrams 9
DFD Symbols
Process symbol Receives input data and produces output that has a
different content, form, or both Contain the business Referred to as a
logic, also called business rules
black box
Data Flow Diagrams 10
สงิ" ทีค" วรทราบ ชอื" มีความหมายชดั เจนในการอธิบายกิจกรรม เชน่ เพิม" รายวิชา หรือ produce report
จะต ้องมีหมายเลขกํากับเสมอ ชอื" process และหมายเลขจะซํ ากันไม่ได ้
Data Flow Diagrams 11
DFD Symbols Data
flow symbol
Represents one
or more data items The symbol for a data flow is a line with a single or double arrowhead
Data Flow Diagrams 12
Spontaneous generation
Black hole
Gray hole
Data Flow Diagrams 13
สงิ" ทีค" วรทราบ
ื" ของ Data flow จะต ้องเป็ นคํานามทีอ ชอ " ธิบายข ้อมูลเสมอ ่ รหัสหนังสอ ื นํ าหนักสน ิ ค ้า ข ้อมูลลูกค ้า เชน
ื" ข ้อมูลมากกว่า 1 ชอ ื" บนเสนเช ้ อ ื" มโดยใช ้ อนุโลมให ้เขียนชอ เครือ " งหมาย comma ชว่ ยแยก
ื" มโยง Data flow จะโยงให ้มีความเชอ ื" มต่อสมบูรณ์ การเชอ ่ งว่าง ไม่มช ี อ
Data Flow Diagrams 14
DFD Symbols
Data store symbol Represent data that
the system stores The physical characteristics of a data store are unimportant because you are concerned only with a logical model
Data Flow Diagrams 15
สงิ" ทีค" วรทราบ
Data store อาจเป็ นการเก็บข ้อมูลในรูปแบบต่างๆกันก็ได ้ ่ สมุดลงนาม แฟ้ มเอกสาร หรือ computer file เชน โครงสร ้างข ้อมูลทีเ" ก็บใน Data store หนึง " ๆจะมีรป ู แบบ เดียวกันทัง หมด มีหมายเลขกํากับ และเลขเหล่านีซ ํ าไม่ได ้ ในการเขียน Data store จะต ้องมี diagram ทีแ " สดงว่า ้ นํ าเข ้ามูลเข ้า รวมทัง มีการนํ าข ้อมูลไปใชงาน
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Data Flow Diagrams 17
DFD Symbols
Entity Symbol Name of
the entity appears inside the symbol Terminators Source Sink
Data Flow Diagrams 18
สงิ" ทีค" วรทราบ
ื" มโยง external entity ตรงๆไม่ได ้ เชอ ื" ม external entity กับ data store ไม่ได ้ เชอ
Data Flow Diagrams 19
Data Flow Diagrams 20
Creating a Set of DFDs 21
Create a graphical model of the information system based on your fact-finding results
First, you will review a set of guidelines for drawing DFDs. Then you will learn how to apply these guidelines and create a set of DFDs using a three-step process
Creating a Set of DFDs 22
Guidelines for Drawing DFDs
Draw the context diagram so that it fits on one page
Use the name of the information system as the process name in the context diagram
Use unique names within each set of symbols ชือ ่ เดียวกันหมายถึงสิ่ งเดียวกัน
Creating a Set of DFDs 23
Guidelines for Drawing DFDs
Do not cross lines
Provide a unique name and reference number for each process
Obtain as much user input and feedback as possible
Creating a Set of DFDs 24
Step 1: Draw a Context Diagram
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ในการเขียน Context diagram
ไม่ให ้มี Data store ใน context diagram
ั ลักษณ์ process ให ้มีสญ ได ้เพียงรูปเดียว
ไม่ควรเขียน External entity ซํ า
ไม่มล ี ก ู ศร 2 ทาง
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กรณีทม ี" ากกว่า 1 data flow สามารถเขียน ้ รวบเสนได ้
Creating a Set of DFDs 27
Step 2: Draw a Diagram 0 DFD
Creating a Set of DFDs 28
Step 2: Draw a Diagram 0 DFD (cont)
If same data flows in both directions, you can use a doubleheaded arrow
Diagram 0 is an exploded view of process 0
Parent diagram
Child diagram
Functional primitive
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DFD Level 0
Context diagram
Creating a Set of DFDs 30
Step 3: Draw the LowerLevel Diagrams Must use leveling and balancing techniques Leveling examples Uses a series of increasingly detailed DFDs to describe an information system Exploding, partitioning, or decomposing
DFD Level 1
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Parent diagram
Child diagram
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การเขียนโดย ไม่แสดง External entity
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Creating a Set of DFDs 34
Step 3: Draw the Lower-Level Diagrams
Balancing Examples Ensures that the input and output data flows of the parent DFD are maintained on the child DFD
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Exercise: find the mistakes 36
Data Dictionary 37
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A data dictionary, or data repository, is a central storehouse of information about the system’s data
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An analyst uses the data dictionary to collect, document, and organize specific facts about the system
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Also defines and describes all data elements and meaningful combinations of data elements
Data Dictionary 38
A data element, also called a data item or field, is the smallest piece of data that has meaning
Data elements are combined into records, also called data structures
A record is a meaningful combination of related data elements that is included in a data flow or retained in a data store
Data Dictionary 39
Using CASE Tools for Documentation
The more complex the system, the more difficult it is to maintain full and accurate documentation
Modern CASE tools simplify the task
A CASE repository ensures data consistency
Data Dictionary Documenting the Data Elements You must document every data element in the data dictionary The objective is the same: to provide clear, comprehensive information about the data and processes that make up the system
Data Dictionary 41
Documenting the Data Elements (cont)
The following attributes usually are recorded and described Data element name and label Alias Type and length Default value Acceptable values - Domain and validity rules
Data Dictionary 42
Documenting the Data Elements (cont)
The following attributes usually are recorded and described Source Security Responsible user(s) Description and comments
example 43
Info for a data element names SOCIAL SECURITY NUMBER System: payroll Label: system security number Alias: SSN Type and length: 9N Default value: none Source: employee application form Acceptable values: any positive number (domain) Security: payroll department User responsibility: payroll department
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Data Dictionary 45
Documenting the Data Flows
The typical attributes are as follows Data flow
name or label
Description Alternate name(s) Origin (source
for data flow can be a process, a data
store, or an entity) Destination (DFD ending point)
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Record
Each data flow represents a group of related data elements called a record or data structure
In most DD, records are defined separately from the data flow and data store.
more than one data flow or data store can use the same record
Volume and frequency
Expected number of occurrences for a data flow per unit of time e.g. 300 time cards per week
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Data Dictionary 48
Documenting the Data Stores
Typical characteristics of a data store are Data store name
or label as
it appears on DFD Description Alternate name(s) Attributes Volume and frequency
Data Dictionary 49
Documenting the Processes
Typical characteristics of a process Process name
or label
Description Process number Process description
Data Dictionary 50
Documenting the Entities
Typical characteristics of an entity include Entity name Description Alternate name(s) Input data flows Output data flows
Data Dictionary 51
Documenting the Records
Typical characteristics of a record include Record or
data structure
name Definition or
description
Alternate name(s) Attributes
Data Dictionary 52
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Data Dictionary Reports –
Many valuable reports •
An alphabetized list of all data elements by name
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A report describing each data element and indicating the user or department that is responsible for data entry, updating, or deletion
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A report of all data flows and data stores that use a particular data element
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Detailed reports showing all characteristics of data elements, records, data flows, processes, or any other selected item stored in the data dictionary
Process Description Tools 53
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A process description documents the details of a functional primitive, which represents a specific set of processing steps and business logic
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It should be noted that this chapter deals with structured analysis, but the process description tools also can be used in object-oriented development, which is described in Chapter 6
Process Description Tools 54
Modular Design
Based on combinations of three logical structures, sometimes called control structures, which serve as building blocks for the process Sequence Selection Iteration - looping
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Process Description Tools 56
Structured English
Must conform to the following rules Use only
the three building blocks of sequence,
selection, and iteration Use indentation for Use a
readability
limited vocabulary, including standard terms used
in the data dictionary and specific words that describe the processing rules
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Input data flows: order, credit status, product detail Output data flows: rejected order, accepted order
For each ORDER if CUSTOMER STATUS CODE = ‘Y’ and PRODUCT DETAIL = ‘OK’ then output ACCEPTED ORDER else output REJECTED ORDER
Process Description Tools 59
Structured English
Might look familiar to programming students because it resembles pseudocode
The primary purpose of structured English is to describe the underlying business logic
Process Description Tools 60
Decision Tables
Shows a logical structure, with all possible combinations of conditions and resulting actions
It is important to consider every possible outcome to ensure that you have overlooked nothing
Process Description Tools 61
Decision Tables
The number of rules doubles each time you add a condition
Can have more than two possible outcomes
Often are the best way to describe a complex set of conditions
Table with two conditions 62
An order will be accepted only if the product is in stock and the customer’s credit status is OK
Table with three conditions 63
• An order will be accepted only if the product is in stock and the customer’s credit status is OK • The credit manager can waive the credit status requirement
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การ Simplify ตาราง
Multiple outcomes 65
• Preferred customers who order $1,000 or more are entitled to a 5% discount, and an additional 5% discount if they use our charge card • Preferred customers who do not order $1,000 or more will receive a $25 coupon • All other customers will receive a $5 bonus coupon
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Process Description Tools 67
Decision Trees
Logical Versus Physical Models 68
While structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information system
A physical model shows how the system’s requirements are implemented
Logical Versus Physical Models 69
Sequence of Models
Many systems analysts create a physical model of the current system and then develop a logical model of the current system before tackling a logical model of the new system
Performing that extra step allows them to understand the current system better
Logical Versus Physical Models 70
Four-Model Approach
Develop a physical model of the current system, a logical model of the current system, a logical model of the new system, and a physical model of the new system
The only disadvantage of the four-model approach is the added time and cost
Chapter Summary 71
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During data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful information
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The end product of data and process modeling is a logical model that will support business operations and meet user needs
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Data and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions
Chapter Summary 72
Data flow diagrams (DFDs) graphically show the movement and transformation of data in the information system
DFDs use four symbols A set of DFDs is like a pyramid with the context diagram at the top
Chapter Summary 73
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The data dictionary is the central documentation tool for structured analysis
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Each functional primitive process is documented using structured English, decision tables, and decision trees
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Structured analysis tools can be used to develop a logical model during one systems analysis phase, and a physical model during the systems design phase
Apply your knowledge 74
Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s website, the system checks to see if the items are in stock, issues a status message to the customer, and generates a shipping order to warehouse, which fills the order. When the order is shipped, the customer is billed. The system also produces various reports.
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1. 2.
Draw a context diagram for the order system Draw a diagram 0 DFD for the order system
