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IS 421 Information Systems Analysis

IS 421 Information Systems Analysis. James Nowotarski 28 October 2002. Today’s Objectives. Practice data flow diagramming Understand requirements for assignment 4 and quiz 3. Course Map. Contents 1. Introduction Planning Phase 2. Project Initiation 3. Project Management

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IS 421 Information Systems Analysis

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  1. IS 421Information Systems Analysis James Nowotarski 28 October 2002

  2. Today’s Objectives • Practice data flow diagramming • Understand requirements for assignment 4 and quiz 3

  3. Course Map Contents 1. Introduction Planning Phase 2. Project Initiation 3. Project Management Analysis Phase 4. Systems Analysis 5. Gathering Information 6. Process Modeling 7. Data Modeling 1 2 3 4 5 6 7 8 9 10 11 Week Core Exam Review Assignments Quizzes Final

  4. Develop ProcessModel Prepare Proposal Develop Data Model Dev Analysis Plan Examine- As-is Identify Improve- ments Develop Basic System Concepts Process Modeling in the Analysis Phase From Planning Phase: Develop Concept for To-Be System System request Feasibility analysis Workplan . . . To Design Phase: Deliverables: Analysis Plan Functional Requirements Quality Requirements Data Model Process Model System Proposal System Concept

  5. Today’s agenda Topic Duration • Grading System Exercise 60 minutes *** Break 15 minutes • DFD 60 minutes • ATB Homework 45 minutes • Assignment 4 and Quiz 3 Intro 10 minutes

  6. Today’s agenda Topic Duration • Grading System Exercise 60 minutes *** Break 15 minutes • DFD 60 minutes • ATB Homework 45 minutes • Assignment 4 and Quiz 3 Intro 10 minutes

  7. Grading System Exercise

  8. Grading System ERD

  9. Grading System DFD Context

  10. Grading System DFD Level 0

  11. Problem statement Al Burns is the professor for the class. He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect. He also creates a list of assignments, a description for each assignment, and a grading key for each one. Students complete the assignment and give them to Al Burns. Al Burns collects the assignments and gives them to Ms. Grader for grading. Ms. Grader grades the assignments based on a key provided by Al Burns, and assigns a score (grade) from 0 to 5. She then records the scores for the students on the spreadsheet. Grades are reported back to students via a course web page created from the spreadsheet. Assignment: Draw a context diagram and level 0 diagram for the Grading System.

  12. DFD Step-by-Step (1) Al Burns is the professor for the class.

  13. DFD Step-by-Step (2) He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect. Can’t show it this way, can’t have a data flow going from external entity to external entity

  14. DFD Step-by-Step (2) He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect.

  15. DFD Step-by-Step (3) He also creates a list of assignments, a description for each assignment, and a grading key for each one.

  16. DFD Step-by-Step (4) Students complete the assignment and give them to Al Burns.

  17. DFD Step-by-Step What about distributing the assignment? (4) Students complete the assignment and give them to Al Burns.

  18. DFD Step-by-Step (5) Al Burns collects the assignments and gives them to Ms. Grader for grading.

  19. DFD Step-by-Step (6) Ms. Grader grades the assignments based on a key provided by Al Burns, and assigns a score (grade) from 0 to 5.

  20. DFD Step-by-Step (7) She then records the scores for the students on the spreadsheet.

  21. DFD Step-by-Step (8) Grades are reported back to students via a course web page created from the spreadsheet.

  22. Today’s agenda Topic Duration • Grading System Exercise 60 minutes *** Break 15 minutes • DFD 60 minutes • ATB Homework 45 minutes • Assignment 4 and Quiz 3 Intro 10 minutes

  23. Data Flow Diagrams

  24. DFD Elements

  25. Key Definitions • A process model is a formal way of representing business processes • Illustrates processes/activities and how data moves among them • Data flow diagramming is a technique for creating a process model. • The primary output of data flow diagramming is a data flow diagram (DFD)

  26. Key Definitions • Logical process models describe processes without suggesting how they are conducted • Physical models include information about how the processes are implemented

  27. Which is the best starting point for developing a system: Data model? Process model? Data vs. Process

  28. Some Rules for External Entities • External people, organizations, systems and data stores • Reside outside the system, but interact with system • Either receive info from system (“sink”) or provide data to the system (“source”) • Examples: Customers, managers • Not clerks or other staff • No relation to entities that are part of ERD -- Unfortunate duplication of terminology External Entities

  29. Some Rules for Data Stores • Internal to the system • Data at rest • Include in system if the system processes transform the data • Create, Update, Delete • Every data store on DFD should correspond to an entity on an ERD • Must have at least one input data flow (or else they never contain any data) • Usually have at least one output data flow • Data can only enter a data store from a process and can only leave a data store to a process D1 Data Stores

  30. Some Rules for Data Flows • Data in motion • From external entity (“source”) to system • From system to external entity (“sink”) • From internal symbol to internal symbol, but always either start or end at a process • Not designed to show materials flow, just data Data Flow

  31. Some Rules for Processes 0. • Always internal to system • Transforms inputs to outputs • Law of conservation of data: #1: Data stays at rest unless moved by a process. #2: Processes cannot consume or manufacture data • Must have at least 1 input data flow (to avoid miracles) • Must have at least 1 output data flow (to avoid black holes) • Should have sufficient inputs to create outputs (to avoid gray holes) Processes

  32. Creating Data Flow Diagrams Creating DFDs is a highly iterative process of gradual refinement. General steps: 1. Create Use Cases/textual requirements descriptions 2. Create a Context diagram 3. Create DFD fragments for each use case/requirement 4. Create a Level 0 diagram from fragments 5. Decompose to Level 1,2,… 6. Go to step 1 and revise as necessary 7. Validate DFDs with users.

  33. Creating Use Cases

  34. Step 1. Use Cases • Use case=Set of activities that the system performs to produce some output result • “Means to an end” - Use case is a more user-friendly way to start working with users to define process model • Use case info is transformed to DFD later • Use case is a tool for end users, not programmers • Creating use cases is an iterative process

  35. Create DFDs Process modeling business process info use case reports data flow diagrams Users To Design Prepare use cases • Easier for users to work with than DFDs • Info gathered through interviews, JAD, etc.

  36. Step 1. Use Cases • Anatomy of a use case (see pp.155, 162): • Name • Short description • Triggers (system is at rest until trigger event occurs) • External (e.g., customer calls) • Temporal (e.g., payment is overdue) • Inputs • Outputs • Steps

  37. Step 1. Use Cases Transforming use case to DFD • Use case name becomes a process name on the level 0 DFD • Major inputs become data flows • Major outputs become data flows • Major steps performed become process names on the level 1 DFD • Destination corresponds to data store or external entity

  38. Creating Data Flow Diagrams

  39. Steps in Building DFDs 2. Create the context diagram 3. Create DFD fragments for each use case 4. Organize DFD fragments into level 0 diagram 5. Decompose level 0 DFDs as needed 6. Go to step 1 and revise as necessary 7. Validate DFDs with users.

  40. Shows the context into which the business process fits Shows the overall business process as just one process Shows all the external entities and the data flows into and out of the system from them Step 2. Context Diagram

  41. Draw the overall system as a process. Number the process 0. Label the process as the name of the system. Draw and label all external entities. No data stores, unless external. Draw data flows for all possible data coming from or going to external entities Bundle data flows as you deem necessary Step 2. Context Diagram

  42. Context Diagram Example

  43. Step 3. Create DFD Fragments • For each use case, create a DFD fragment. • One process (verb phrase) per fragment • Maintain organization’s viewpoint in naming processes • Layouts often place: • Process in the center • Inputs from the left • Outputs to the right • Add data stores beneath the processes

  44. DFD Fragment Example

  45. Integrate DFD fragments to a Level 0 DFD There will be one Level 0 diagram, Shows all the processes that comprise the overall system A decomposition of the process on the context diagram Shows how information moves from and to each process Step 4. Level 0 Diagram

  46. Level 0 Tips • Generally move from top to bottom, left to right • Minimize crossed lines • Iterate as needed • The DFD is often drawn many times before it is finished, even with very experienced systems analysts • Data stores are not usually included

  47. 2 1 3 4 Delete patient Find patient Update patient Add new patient DFD Example Patient Patient information to delete Patient name Patient info to be updated Deleted patient Patient information D1 Patient Information Updated patient information Changes to patient information Patient information New patient information

  48. Some Data Flow Rules A process moves data from place to place in the system. On a data flow diagram, processes may move data between certain symbols (data stores, external entities, and other processes). However, data may not be moved without a process. To help you understand and appreciate this, fill in the empty cells in the following table. The cell entries should either be 1) An example of how data could be moved; 2) N/A to indicate this cannot be done. In this example, “customer information” may be moved from an external entity to a process (e.g., a customer gives their address and credit card information to a sales agent). The “N/A” suggests data cannot be moved from a data store directly to an external entity, which is true (you need a process in between them).

  49. Relationship Among DFD levels

  50. A major step on the use case is usually a process on the Level 1 DFD Level 1 DFD shows all the processes that comprise a single process on the level 0 diagram Inputs to step are input data flows to process Outputs to step are output data flows from process In general, # level 1 DFDs =# of processes on level 0 DFD Step 5. Level 1 Diagrams

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