Ch05_Data_Process_Modeling.pdf

Systems Analysis and Design, 13 th Edition Chapter 5: Data & Process Modeling Scott Tilley, Sy...

Systems Analysis and Design, 13 th Edition Chapter 5: Data & Process Modeling Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1  Chapter Objectives (1 of 2) By the end of this chapter, you should be able to: 1. Describe the relationship between logical and physical models. 2. Explain data flow diagrams. 3. Draw the four basic data flow diagram symbols. 4. Explain the six guidelines used when drawing data flow diagrams. 5. Draw context diagrams. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 2  Chapter Objectives (2 of 2) By the end of this chapter, you should be able to (continued): 6. Draw diagram 0 data flow diagrams. 7. Draw lower-level data flow diagrams. 8. Create a data dictionary. 9. Apply process description tools in modular design. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 3  Logical versus Physical Models A logical model shows what the system must do, regardless of how it will be implemented physically A physical model describes how the system will be constructed Many analysts follow a four-model approach which develops: − A physical model of the current system − A logical model of the current system − A logical model of the new system − A physical model of the new system Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 4  Data Flow Diagrams A data flow diagram (DFD) uses various symbols to show how the system transforms input data into useful information A 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 Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 5  Data Flow Diagram Symbols (1 of 13) Data flow diagrams use four basic symbols representing processes, data flows, data stores, and entities Several versions of DFD symbols exist DFD examples in this textbook use Gane and Sarson symbols Yourdon symbols are another popular set Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6 Data Flow Diagram Symbols (2 of 13) Figure 5-1 Data flow diagram symbols and symbol names. The examples use Gane and Sarson symbols and Yourdon symbols. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 7  Data Flow Diagram Symbols (3 of 13) Process Symbols − Processes contain business logic which transform data and produce the required results − The process name on the symbol identifies a function consisting of a verb followed by a singular noun  For example: APPLY RENT PAYMENT − A process symbol can be called a black box because the process’s inputs, outputs, and functions are known, but underlying logic is hidden Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 8  Data Flow Diagram Symbols (4 of 13) Data Flow Symbols − A data flow is a path for data to move from one part of the information system to another − A data flow in a DFD represents one or more data items − The symbol for a data flow is a line with a single or double arrowhead − A data flow name includes a singular noun and an adjective (if needed) Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 9 Data Flow Diagram Symbols (5 of 13) Figure 5-3 Examples of correct data flow and process symbol combinations. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 10 Data Flow Diagram Symbols (6 of 13) Figure 5-4 Examples of incorrect data flow and process symbol combinations. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 11  Data Flow Diagram Symbols (7 of 13) A data store is used in a DFD to represent data that the system stores because one or more processes need to use the data later In a DFD, the Gane and Sarson symbol for a data store is a flat rectangle that is open on the right side and closed on the left A data store name is a plural name consisting of a noun and adjectives (if needed) A data store must be connected to a process with a data flow Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 12 Data Flow Diagram Symbols (8 of 13) Figure 5-5 Examples of correct use of data store symbols in a DFD. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 13 Data Flow Diagram Symbols (9 of 13) Figure 5-6 Examples of incorrect use of data store symbols in a DFD. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 14  Data Flow Diagram Symbols (10 of 13) The symbol for an entity is a rectangle, which may be shaded to make it look three-dimensional A DFD shows only external entities that provide data to the system or receive output from the system DFD entities also are called terminators because they are data origins or final destinations An entity that supplies data to the system is called a source An entity that receives data from the system is called a sink Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 15 Data Flow Diagram Symbols (11 of 13) Figure 5-7 Examples of correct uses of external entities in a DFD. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16 Data Flow Diagram Symbols (12 of 13) Figure 5-8 Examples of incorrect uses of external entities in a DFD. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 17 Data Flow Diagram Symbols (13 of 13) Figure 5-9 Examples of correct and incorrect uses of data flows. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 18  Knowledge Check Activity 5-1 What is the relationship between logical and physical models? Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 19  Knowledge Check Activity 5-1: Answer What is the relationship between logical and physical models? Answer: A logical model shows what the system must do, regardless of how it will be implemented physically. Later, in the systems design phase, a physical model is built that describes how the system will be constructed. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 20  Drawing Data Flow Diagrams The following are guidelines to drawing a data flow diagram: − 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 − Do not cross lines − Provide a unique name and reference number for each process − Ensure that the model is accurate, easy to understand, and meets the needs of its users Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 21  Drawing a Context Diagram (1 of 2) A context diagram is a top-level view of an information system that shows the system’s boundaries and scope To draw a context diagram, start by placing a single process symbol in the center of the page − The symbol represents the entire information system and is identified as process 0 Place the system entities around the perimeter of the page and use data flows to connect the entities to the central process Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 22 Drawing a Context Diagram (2 of 2) Figure 5-11 Context diagram DFD for an order system. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 23  Drawing a Diagram 0 DFD (1 of 2) Diagram 0 provides an overview of all the components that interact to form the overall system It zooms in on the system and shows major internal processes, data flows, and data stores − It also repeats the entities and data flows in the context diagram When the context diagram is expanded into DFD diagram 0, all the connections that flow into and out of process 0 must be retained A diverging data flow occurs when the same data travels to two or more locations Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 24 Drawing a Diagram 0 DFD (2 of 2) Figure 5-12 Context diagram and diagram 0 for the grading system. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 25  Drawing Lower-Level DFDs (1 of 4) Leveling draws increasing detailed diagrams until all functional primitives are identified Balancing maintains consistency among DFDs by ensuring that input and output data flows align properly Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 26 Drawing Lower-Level DFDs (2 of 4) Figure 5-16 The order system diagram 0 is shown at the top of the figure, and the exploded diagram 3 DFD (for the APPLY PAYMENT process) is shown at the bottom. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 27 Drawing Lower-Level DFDs (3 of 4) Figure 5-17 Example of a parent DFD, showing process 0 as a black box. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 28 Drawing Lower-Level DFDs (4 of 4) Figure 5-18 In the next level of detail, the process 0 black box reveals three processes, two data stores, and four internal data flows – all shown inside the dashed line. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 29  Knowledge Check Activity 5-2 What is the difference between a context diagram and diagram 0? Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 30  Knowledge Check Activity 5-2: Answer What is the difference between a context diagram and diagram 0? Answer: The context diagram contains only one process symbol, process 0, representing the entire system. Diagram 0 is a more detailed (or exploded, partitioned, or decomposed) version of process 0 on the context diagram. The major processes, data flows, and data stores for the information system are shown in diagram 0. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 31  Data Dictionary (1 of 8) A data dictionary contains information about data, such as its meaning, relationships to other data, origin, usage, and format A data dictionary typically includes the following: − Data element descriptions (also called a data item or field) − Attribute/property definitions − Relationship descriptions − Rules and constraints − Other metadata Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 32  Data Dictionary (2 of 8) Every data element in the data dictionary should be documented − The objective is to provide clear, comprehensive information about the data and processes that make up a system The following data element attributes are usually documented in the data dictionary: − Data element name, alias, type and length, default value, acceptable values, source, security, responsible user(s), and description/comments Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 33  Data Dictionary (3 of 8) All data flows in the data dictionary must be documented Typical attributes include the following: − Data flow name or label − Description − Alternate name(s) − Origin − Destination − Record − Volume and frequency Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 34  Data Dictionary (4 of 8) Every DFD data store in the data dictionary must be documented Typical characteristics of a data store include the following: − Data store name or label − Description − Alternate name(s) − Attributes − Volume and frequency Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 35  Data Dictionary (5 of 8) Every DFD process in the data dictionary must be documented Typical characteristics of a process include the following: − Process name or label − Description − Process number − Process description – This section includes the input and output data flows Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 36  Data Dictionary (6 of 8) External entities in the data dictionary should be documented Typical characteristics of a process include the following: − Entity name − Description − Alternate name(s) − Input data flows − Output data flows Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 37  Data Dictionary (7 of 8) A record is a data structure containing related data elements stored and processed together Records in the data dictionary should be documented Typical characteristics of a process include the following: − Record or data structure name − Definition or description − Alternate name(s) − Attributes Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 38  Data Dictionary (8 of 8) The following are reports that can be obtained from a data dictionary: − An alphabetized list of all data elements − A report describing each data element and indicating the user or department − 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 Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 39  Process Description Tools in Modular Design (1 of 8) A process description documents the details of a functional primitive and represents a specific set of processing steps and business logic − Typical process description tools include structured English, decision tables, and decision trees Process descriptions in object-oriented development − O-O analysis combines data and processes that act on the data into objects, and similar objects can be grouped together into classes − O-O processes are called methods Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 40  Process Description Tools in Modular Design (2 of 8) Modular design is based on combinations of three logical structures (i.e., control structures), which serve as building blocks for the process The three structures are called a sequence, selection, and iteration − A rectangle represents a step or process − A diamond shape represents a condition or decision − The logic follows the lines in the direction indicated by the arrows Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 41 Process Description Tools in Modular Design (3 of 8) Figure 5-20 Sequence structure Figure 5-21 Selection structure Figure 5-22 Iteration structure Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 42  Process Description Tools in Modular Design (4 of 8) Structured English is a subset of standard English that describes logical processes clearly and accurately − Use only the three building blocks of sequence, selection, and iteration − Use indentation for readability − Use a limited vocabulary Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 43  Process Description Tools in Modular Design (5 of 8) A decision table is a logical structure that shows every combination of conditions and outcomes − If a process has a single condition, there are only two possibilities – yes or no (there are only two rules) − The number of rules doubles each time a condition is added Decision tables can be created using Microsoft PowerPoint, Word, or Excel A decision table is the best way to describe a complex set of conditions Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 44 Process Description Tools in Modular Design (6 of 8) Figure 5-24 Example of a simple decision table showing the processing logic of the VERIFY ORDER process. To create the table, follow the four steps shown. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 45  Process Description Tools in Modular Design (7 of 8) A decision tree is a graphical representation of conditions, actions, and rules found in a decision table Decision trees show the logic structure in a horizontal form that resembles a tree with the roots at the left and the branches to the right Decision trees and decision tables provide the same results but in different forms Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 46 Process Description Tools in Modular Design (8 of 8) Figure 5-26 This decision tree example is based on the same sales promotion policy shown in the decision tables in Tables 5-5 and 5-6 (see textbook). Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 47  Knowledge Check Activity 5-3 What is the purpose of a decision table? Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 48  Knowledge Check Activity 5-3: Answer What is the purpose of a decision table? Answer: A decision table is a logical structure that shows every combination of conditions and outcomes. Analysts often use decision tables to describe a process and ensure they have considered all possible situations. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 49  Self Assessment How would you level a data flow diagram? What is a data element? Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 50  Summary (1 of 2) Now that the lesson has ended, you should be able to: 1. Describe the relationship between logical and physical models. 2. Explain data flow diagrams. 3. Draw the four basic data flow diagram symbols. 4. Explain the six guidelines used when drawing data flow diagrams. 5. Draw context diagrams. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 51  Summary (2 of 2) Now that the lesson has ended, you should be able to (continued): 6. Draw diagram 0 data flow diagrams. 7. Draw lower-level data flow diagrams. 8. Create a data dictionary. 9. Apply process description tools in modular design. Scott Tilley, Systems Analysis and Design, 13th Edition. © 2025 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 52