IT 352: Information Systems Analysis and Design 2020 PDF

IT 352: Information Systems Analysis and Design By: Haifa Alhasson 2020 Copyright © 2011 Pearson Education, Inc. Publishing as 10/25/20 Chapte...

IT 352: Information Systems Analysis and Design By: Haifa Alhasson 2020 Copyright © 2011 Pearson Education, Inc. Publishing as 10/25/20 Chapter 3 Prentice Hall 1 Brief List of Topics Overview of Information System development environment The origin of Software Managing the Information Systems Project Identifying and Selecting Systems Development Projects Initiating and Planning Systems Development Projects Determine the system requirements Structuring System Process Requirements Designing information systems System Implementation Maintaining Information Systems Copyright © 2011 Pearson Education, Inc. Publishing as 10/25/20Chapter 2 Prentice Hall 2 Modern Systems Analysis and Design Chapter 7 Structuring System Process Requirements  Learning Objectives ü Understand the logical modeling of processes by studying examples of data flow diagrams (DFDs). ü Draw data flow diagrams following specific rules and guidelines that lead to accurate and well-structured process models. ü Decompose data flow diagrams into lower-level diagrams. ü Balance higher-level and lower-level data flow diagrams. 4  Learning Objectives (Cont.) ü Use data flow diagrams as a tool to support the analysis of information systems. ü Discuss process modeling for electronic commerce applications. ü Use decision tables to represent the logic of choice in conditional statements. 5  Process Modeling FIGURE 7-1 Systems development life cycle with the analysis phase highlighted 6  Process Modeling (Cont.) n Graphically represent the processes that capture, manipulate, store, and distribute data between a system and its environment and among system components. 7  Process Modeling (Cont.) n Utilize information gathered during requirements determination. n Processes and data structures are modeled. 8  Deliverables and Outcomes n Context data flow diagram (DFD) ¨ Scope of system n DFDs of current physical system ¨ Adequate or sufficient detail only n DFDs of current logical system ¨ Enables analysts to understand current system 9  Deliverables and Outcomes (Cont.) n DFDs of new logical system ¨ Technology independent ¨ Show data flows, structure, and functional requirements of new system n Thorough description of each DFD component 10  Data Flow Diagramming Mechanics n Represent both physical and logical information systems n Only four symbols are used 11 Data Flow Diagramming Mechanics (Cont.) n Useful for depicting purely logical information flows n DFDs that detail physical systems differ from system flowcharts which depict details of physical computing equipment 12 Definitions and Symbols FIGURE 7-2 Comparison of DeMarco and Yourdon and Gane and Sarson DFD symbol sets 13  Definitions and Symbols (Cont.) n Process: work or actions performed on data (inside the system) n Data store: data at rest (inside the system) 14  Definitions and Symbols (Cont.) n Source/sink: external entity that is origin or destination of data (outside the system) n Data flow: arrows depicting movement of data 15  Developing DFDs n Context diagram is an overview of an organizational system that shows: ¨ the system boundaries. ¨ external entities that interact with the system. ¨ major information flows between the entities and the system. n Note: only one process symbol, and no data stores shown 16  Context Diagram FIGURE 7-4 Context diagram of Hoosier Burger’s food-ordering system 17  Developing DFDs (Cont.) n Level-0 diagram is a data flow diagram that represents a system’s major processes, data flows, and data stores at a high level of detail. ¨ Processes are labeled 1.0, 2.0, etc. These will be decomposed into more primitive (lower-level) DFDs. 18  Level-0 Diagram FIGURE 7-5 Level-0 DFD of Hoosier Burger’s 19 food-ordering system  Data Flow Diagramming Rules n There are two DFD guidelines that apply: ¨ The inputs to a process are different from the outputs of that process. n Processes purpose is to transform inputs into outputs. ¨ Objects on a DFD have unique names. n Every process has a unique name. 20 Data Flow Diagramming Rules (Cont.) TABLE 7-2 Rules Governing Data Flow Diagramming 21 Data Flow Diagramming Rules (Cont.) TABLE 7-2 Rules Governing Data Flow Diagramming (cont.) 22  Decomposition of DFDs n Functional decomposition is an iterative process of breaking a system description down into finer and finer detail. ¨ Creates a set of charts in which one process on a given chart is explained in greater detail on another chart. ¨ Continues until no sub process can logically be broken down any further. 23  Decomposition of DFDs (Cont.) n Primitive or old DFD is the lowest level of a DFD. n Level-1 diagram results from decomposition of Level-0 diagram. n Level-n diagram is a DFD diagram that is the result of n nested decompositions from a process on a level-0 diagram. 24  Level-1 DFD FIGURE 7-8 Level-1 diagram showing the decomposition of Process 4.0 from the level-0 diagram for Hoosier Burger’s food-ordering system Level-1 DFD shows the sub-processes of one of the processes in the Level-0 DFD. Processes are labeled 4.1, 4.2, etc. This is a Level-1 DFD These can be further decomposed in for Process 4.0. more primitive (lower-level) DFDs if necessary. 25 Level-n DFD FIGURE 7-9 Level-2 diagram showing the decomposition of Process 4.3 Level-n DFD shows from the level-1 diagram for Process 4.0 for Hoosier Burger’s the sub-processes of food-ordering system one of the processes in the Level n-1 DFD. This is a Level-2 DFD for Process 4.3. Processes are labeled 4.3.1, 4.3.2, etc. If this is the lowest level of the hierarchy, it is called a primitive DFD. 26 Some Common Errors 27  Balancing DFDs n Conservation Principle: conserve inputs and outputs to a process at the next level of decomposition n Balancing: conservation of inputs and outputs to a data flow diagram process when that process is decomposed to a lower level 28  Balancing DFDs (Cont.) n Balanced means: ¨ Number of inputs to lower level DFD equals number of inputs to associated process of higher-level DFD ¨ Number of outputs to lower level DFD equals number of outputs to associated process of higher-level DFD 29  Balancing DFDs (Cont.) (a) Context diagram 1 input This is unbalanced 1 output because the process of the (b) Level-0 diagram context diagram has only one input but the Level-0 diagram has two 2 inputs inputs. 1 output FIGURE 7-10 An unbalanced set of data flow diagrams 30  Balancing DFDs (Cont.) n Data flow splitting is when a composite data flow at a higher level is split and different parts go to different processes in the lower level DFD. n The DFD remains balanced because the same data is involved, but split into two parts. 31 Balancing DFDs (Cont.) FIGURE 7-11 Example of data flow splitting (a) Composite data flow (b) Disaggregated data flows 32 Balancing DFDs: More DFD Rules 33 Balancing the DFD 34  Four Different Types of DFDs n Current Physical ¨ Describes about “How a system works”. ¨ Process labels identify technology (people or systems) used to process the data. ¨ Data flows and data stores identify actual name of the physical media. 35 Four Different Types of DFDs n Current Logical ¨ Describes about “What a system does”. ¨ Physical aspects of system are removed as much as possible. ¨ Current system is reduced to data and processes that transform them. 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 36  Four Different Types of DFDs (Cont.) n New Logical ¨ Includes additional functions. ¨ Obsoleteoutdated functions are removed. ¨ Inefficient data flows are reorganized. n New Physical ¨ Represents the physical implementation of the new system. 37  Guidelines for Drawing DFDs n Completeness ¨ DFD must include all components necessary for system. ¨ Each component must be fully described in the project dictionary or CASE repository. n Consistency ¨ The extent to which information contained on one level of a set of nested DFDs is also included on other levels ¨ Example of inconsistency would be a data flow that appears on a higher-level DFD but not on lower levels(violation of balancing) 38  Guidelines for Drawing DFDs (Cont.) n Timing ¨ Time is not represented well on DFDs.on a given DFD ,there is no indication of whether a data flow occurs constantly in real time,once per week,or once per year. ¨ Best to draw DFDs as if the system has never started and will never stop. n Iterative Development ¨ Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled. 39  Guidelines for Drawing DFDs (Cont.) n Primitive DFDs ¨ Lowest logical level of decomposition ¨ Decision has to be made when to stop decomposition 40  Guidelines for Drawing DFDs (Cont.) n Rules for stopping decomposition ¨ When each process has been reduced to a single decision, calculation or database operation ¨ When each data store represents data about a single entity 41  Guidelines for Drawing DFDs (Cont.) n Rules for stopping decomposition, cont. ¨ When the system user does not care to see any more detail ¨ When every data flow does not need to be split further to show that data are handled in various ways 42  Guidelines for Drawing DFDs (Cont.) n Rules for stopping decomposition, cont. ¨ When you believe that you have shown each business form or transaction, online display and report as a single data flow ¨ When you believe that there is a separate process for each choice on all lowest-level menu options 43  Using DFDs as Analysis Tools n DFDs can also be used in a process called gap analysis. n Gap Analysis is the process of discovering discrepancies inconsistencies between two or more sets of data flow diagrams or discrepancies within a single DFD. n Inefficiencies in a system can often be identified through DFDs. 44  Using DFDs in BPR FIGURE 7-16 IBM Credit Corporation’s primary work process before BPR (Source: Based on Hammer and Champy, 1993.) 45 Using DFDs in BPR (Cont.) FIGURE 7-17 IBM Credit Corporation’s primary work process after BPR (Source: Based on Hammer and Champy, 1993.) 46  Modeling Logic with Decision Tables n Decision table: a matrix representation of the logic of a decision which specifies the possible conditions for the decision and the resulting actions. n Best used for complicated decision logic. 47 Modeling Logic with Decision Tables (Cont.) FIGURE 7-18 Complete decision table for payroll system example 48  Modeling Logic with Decision Tables (Cont.) n Condition stubs: that part of a decision table that lists the conditions relevant to the decision n Action stubs: that part of a decision table that lists the actions that result for a given set of conditions 49  Modeling Logic with Decision Tables (Cont.) n Rules: that part of a decision table that specifies which actions are to be followed for a given set of conditions n Indifferent condition: in a decision table, a condition whose value does not affect which actions are taken for two or more rules 50  Modeling Logic with Decision Tables (Cont.) n Procedure for Creating Decision Tables ¨ Name the condition and the values that each condition can assume. ¨ Name all possible actions that can occur. ¨ List all possible rules. ¨ Define the actions for each rule. ¨ Simplify the table. 51 Modeling Logic with Decision Tables (Cont.) 52  Electronic Commerce Application: Process Modeling using Data Flow Diagrams n Process modeling for Pine Valley Furniture’s Webstore ¨ Completed JAD session. ¨ Began translating the Webstore system structure into data flow diagrams. n Identified six high-level processes. 53 Electronic Commerce Application: Process Modeling using Data Flow Diagrams (Cont.) 54 Electronic Commerce Application: Process Modeling using Data Flow Diagrams FIGURE 7-22 55 Level-0 data flow diagram for the Web Store Exercise 1 Perfect Pizza wants to install a system to record orders for pizza and chicken wings. When regular customers call Perfect Pizza on the phone, their phone number goes automatically into the Pizza system. The phone number invokes the name, address, and last order date comes automatically up on the screen. Once the order is taken, the total, including tax and delivery, is calculated. Then the order is given to the cook. A receipt is printed. Occasionally, special offer (coupons) is printed so the customer can get a discount. Drivers who make deliveries give customers a copy of the receipt and coupon (if any). Weekly totals are kept for comparison with last year’s performance. § Draw a context diagram for Perfect Pizza § Explode the context-level diagram showing all the major processes © 2011 Pearson Education, Inc. Publishing as Prentice Hall 56  Context Diagram 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 57  Current Logical Level-1 Diagram 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 58  Current Logical Child Diagram 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 59  Current Logical Child Diagram 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 60 Exercise 2 n Model the level-1 flow diagram for Student Registration System based on its context- level diagram. Registration Form Student Registry Student System Confirmed Letter © 2011 Pearson Education, Inc. Publishing as Prentice Hall 61  Open 1.0 course Registration Form Student Verify availability Course o inf t en e urs llm Accepted/reject result ro Co en Co se nf 2.0 ur irm Co ed Enroll Student Le Student info tte r Student Registration updated in fo 3.0 Confirm Registration 10/25/20Chapter 7 © 2011 Pearson Education, Inc. Publishing as Prentice Hall 62 Participance Assignment Model the level-1 flow diagram for Online MSQs Exam Software System based on its context-level diagram. Online MSQs Exam Software System Deadline: Tonight 12 am. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 63  Summary n In this chapter you learned how to: ü Understand logical process modeling via data flow diagrams (DFDs). ü Draw data flow diagrams of well structured process models. ü Decompose data flow diagrams into lower-level diagrams. 64  Summary (Cont.) ü Balance high-level and low-level data flow diagrams. ü Use data flow diagrams for analyzing information systems. ü Use decision tables to represent the logic of choice in conditional statements. 65