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2 Chapter Objectives  Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptions  Describe the symbols used in data flow diagrams and explain the rules for their use  Draw data flow diagrams in a sequence, from general to specific  Explain how to level and balance a set of data flow diagrams

3 Chapter Objectives  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

4 Introduction  In chapter 4 & 5, you will develop a logical model of the proposed system and document the system requirements – Logical model shows what the system must do Logical model – Physical model describes how the system will be constructed Physical model

5 Overview of Data and Process Modeling Tools  Systems analysts use many graphical techniques to describe an information system  A data flow diagrams (DFD) uses various symbols to show how the system transforms input data into useful informationdata flow diagrams (DFD)

6 Data Flow Diagrams  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 Figure 4-2

7 Data Flow Diagrams  DFD Symbols – DFDs use four basic symbols that represent processes, data flows, data stores, and entities Gane and Sarson symbol setGane and Sarson Yourdon symbol setYourdon – Symbols are referenced by using all capital letters for the symbol name Figure 4-3 For more information about Yourdon Symbols visit scsite.com/sad7e/morescsite.com/sad7e/more, locate Chapter 4 and then the Yourdon Symbols link.

8 Data Flow Diagrams  DFD Symbols – Process symbol Process Receives input data and produces output that has a different content, form, or both Contain the business logic, also called business rulesbusiness logicbusiness rules Referred to as a black boxblack box Figure 4-4

9 Data Flow Diagrams  DFD Symbols – Data flow symbol Data flow Represents one or more data items The symbol for a data flow is a line with a single or double arrowhead Spontaneous generation Black hole Gray hole Figure 4-5 Figure 4-6

10 Data Flow Diagrams  DFD Symbols – Data store symbol Data store Represent data that the system stores The physical characteristics of a data store are unimportant because you are concerned only with a logical model Is a flat rectangle that is open on the right side and closed on the left side Figure 4-7 Figure 4-8

11 Data Flow Diagrams  DFD Symbols – Entity Symbol Entity Symbol is a rectangle, which may be shaded to make it look three-dimensional Name of the entity appears inside the symbol Terminators Source Sink Figure 4-9 Figure 4-10 Figure 4-11

12 Creating a Set of DFDs  Create a graphical model of the information system based on your fact-finding results  Three-step process – Step 1: Draw a context diagram – Step 2: Draw a diagram 0 DFD – Step 3: Draw the lower-level diagrams

13 Creating a Set of DFDs  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

14 Creating a Set of DFDs  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

15 Creating a Set of DFDs  Step 1: Draw a Context Diagram – Context diagram Context diagram – Start by placing a single process symbol in the center of the page – Process 0 Process 0 – Identify the entities and the name and content of the data flows, and the direction of the data flows Figure 4-12 Figure 4-13

16 Creating a Set of DFDs  Step 2: Draw a Diagram 0 DFD – Diagram 0 Diagram 0 – Zooms in on the context diagram and shows major processes, data flows, and data stores – Must retain all the connections that flow into and out of process 0 – Each process has a reference number – Diverging data flow Diverging data flow Figure 4-15 Figure 4-14

17 Creating a Set of DFDs  Step 2: Draw a Diagram 0 DFD – If same data flows in both directions, you can use a double-headed arrow – Diagram 0 is an exploded view of process 0 – Parent diagram Parent diagram – Child diagram Child diagram – Functional primitive Functional primitive Figure 4-16

18 Creating a Set of DFDs  Step 3: Draw the Lower-Level Diagrams – Must use leveling and balancing techniqueslevelingbalancing – Leveling examples Uses a series of increasingly detailed DFDs to describe an information system Exploding, partitioning, or decomposingExplodingpartitioningdecomposing Figure 4-17 Figure 4-18

19 Creating a Set of DFDs  Step 3: Draw the Lower-Level Diagrams – Balancing Ensures that the input and output data flows of the parent DFD are maintained on the child DFD Figure 4-20 Figure 4-21 Figure 4-22 Figure 4-19

20 Data Dictionary  A data dictionary, or data repository, is a central storehouse of information about the system’s datadata dictionarydata repository  An analyst uses the data dictionary to collect, document, and organize specific facts about the system  Also defines and describes all data elements and meaningful combinations of data elementsdata elements For more information about Data Dictionaries visit scsite.com/sad7e/morescsite.com/sad7e/more, locate Chapter 4 and then the Data Dictionaries link.

21 Data Dictionary  A data element, also called a data item or field, is the smallest piece of data that has meaningdata item field  Data elements are combined into records, also called data structuresrecordsdata structures  A record is a meaningful combination of related data elements that is included in a data flow or retained in a data store

22 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 Figure 4-23 Figure 4-24

23 Data Dictionary  Documenting the Data Elements – The following attributes usually are recorded and described Data element name and label Alias Type and lengthTypelength Default value Acceptable values - Domain and validity rulesDomainvalidity rules

24 Data Dictionary  Documenting the Data Elements – The following attributes usually are recorded and described Source Security Responsible user(s) Description and comments

25 Data Dictionary  Documenting the Data Flows – The typical attributes are as follows Data flow name or label Description Alternate name(s) Origin Destination Record Volume and frequency Figure 4-25

26 Data Dictionary  Documenting the Data Stores – Typical characteristics of a data store are Data store name or label Description Alternate name(s) Attributes Volume and frequency Figure 4-26

27 Data Dictionary  Documenting the Processes – Typical characteristics of a process Process name or label Description Process number Process description Figure 4-27

28 Data Dictionary  Documenting the Entities – Typical characteristics of an entity include Entity name Description Alternate name(s) Input data flows Output data flows Figure 4-28

29 Data Dictionary  Documenting the Records – Typical characteristics of a record include Record or data structure name Definition or description Alternate name(s) Attributes Figure 4-29

30 Data Dictionary  Data Dictionary Reports – Many valuable reports An alphabetized list of all data elements by name A report describing each data element and indicating the user or department that is responsible for data entry, updating, or deletion A report of all data flows and data stores that use a particular data element Detailed reports showing all characteristics of data elements, records, data flows, processes, or any other selected item stored in the data dictionary

31 Process Description Tools  A process description documents the details of a functional primitive, which represents a specific set of processing steps and business logicprocess description

32 Process Description Tools  Modular Design Modular Design – Based on combinations of three logical structures, sometimes called control structures which serve as building blocks for the processlogical structurescontrol structures 1.SequenceSequence 2.SelectionSelection 3.Iteration - loopingIterationlooping Figure 4-30 Figure 4-31Figure 4-32

33 Process Description Tools  Structured English Structured English – Must conform to the following rules Use only the three building blocks of sequence, selection, and iteration Use indentation for readability Use a limited vocabulary, including standard terms used in the data dictionary and specific words that describe the processing rules For more information about Structured English visit scsite.com/sad7e/morescsite.com/sad7e/more, locate Chapter 4 and then the Structured English link.

34 Process Description Tools  Structured English – Might look familiar to programming students because it resembles pseudocodepseudocode – The primary purpose of structured English is to describe the underlying business logic Figure 4-33 Figure 4-34

35 Process Description Tools  Decision Tables 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 Figure 4-35 Figure 4-36 For more information about Decision Tables visit scsite.com/sad7e/morescsite.com/sad7e/more, locate Chapter 4 and then the Decision Tables link.

36 Process Description Tools  Decision Tables – Decision table – Easy to construct and understand – Can have more than two possible outcomes – Often are the best way to describe a complex set of conditions Figure 4-37

37 Process Description Tools  Decision Trees Decision Trees – Graphical representation of the conditions, actions, and rules found in a decision table – Whether to use a decision table or tree often is a matter of personal preference – Is an effective way to describe a relatively simple process Figure 4-38 Figure 4-39

38 Logical Versus Physical Models  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

39 Logical Versus Physical Models  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

40 Logical Versus Physical Models  Four-Model Approach 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

41 Chapter Summary  During data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful information  The end product of data and process modeling is a logical model that will support business operations and meet user needs  Data and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions

42 Chapter Summary  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

43 Chapter Summary  The data dictionary is the central documentation tool for structured analysis  Each functional primitive process is documented using structured English, decision tables, and decision trees  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

44 Test Yourself 1.True/False: Data flow diagrams show what a system does, not how it does it.

45 Test Yourself 1.True/False: Data flow diagrams show what a system does, not how it does it. True

46 Test Yourself 2.The following symbols are from the _____________ set. Name them:

47 Test Yourself 2.The following symbols are from the Gane and Sarson set. Name them: Data Store Process

48 Test Yourself 3.Select the correct example below. Customer A) B) Apply Payment Accounts Receivable Payment

49 Test Yourself 3.Select the correct example below. A) is correct. An external entity can’t be directly connected to a data store. A)B) Customer Apply Payment Accounts Receivable Payment

50 Test Yourself 4.Match the terms in the left column to the proper definitions in the right column. 1. Black Hole 2. Spontaneous Generation Process 3. Gray Hole a.A process with at least 1 input and output, but the input is insufficient to generate the shown output. b. A process that has no output c. Used to describe an unexplained generation of data or information.

51 Test Yourself 4.Match the terms in the left column to the proper definitions in the right column. 1. Black Hole 2. Spontaneous Generation Process 3. Gray Hole a.A process with at least 1 input and output, but the input is insufficient to generate the shown output. b. A process that has no output c. Used to describe an unexplained generation of data or information.

52 Test Yourself 5.True/False: Diagram 0 is a top-level view that shows the system’s boundaries and scope.

53 Test Yourself 5.True/False: Diagram 0 is a top-level view that shows the system’s boundaries and scope. False

54 Test Yourself 6.List the drawing guidelines for DFDs.

55 Test Yourself 6.List the drawing guidelines for DFDs. 1.Draw the context diagram so that it fits on one page 2.Use the name of the information system as the process name in the context diagram 3.Use unique names within each set of symbols 4.Do not cross lines 5.Provide a unique name and reference number for each process 6.Obtain user input and feedback

56 Test Yourself 7.__________ are way(s) to describe diagram 0 a)Exploded b)Partitioned c)Decomposed d)None of the above e)All of the above

57 Test Yourself 7.__________ are way(s) to describe diagram 0 a)Exploded b)Partitioned c)Decomposed d)None of the above e)All of the above

58 Test Yourself 8.Good design principles dictate that lower- level diagrams go through a ________ and _________ process.

59 Test Yourself 8.Good design principles dictate that lower- level diagrams go through a leveling and balancing process

60 Test Yourself 9.True/False: Decision trees are a graphical representation that show a decision table’s conditions, actions, and rules.

61 Test Yourself 9.True/False: Decision trees are a graphical representation that show a decision table’s conditions, actions, and rules. True

62 Test Yourself 10. List all four models included in the four- model approach.

63 Test Yourself 10. List all four models included in the four- model approach. 1.Physical model of the current system 2.Logical model of the current system 3.Logical model of the new system 4.Physical model of the new system

Systems Analysis & Design 7 th Edition End Chapter 4