Systems Analysis Process Modeling (DFD) 1 of 10. Analysis 003

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1 Systems Analysis Process Modeling (DFD) 1 of 10 Goals: Process modeling (Data flow diagrams) Recognize and describe abstractions Identify the four elements of a DFD Construct a DFD Decompose a DFD Analysis 003 Modeling the System Process models: diagrams how data flows through the system Data model: diagrams the relationships between data files Object model: diagrams the relationships between enterprise objects Systems models: diagram system functions, hardware, and software DFD and the Six CIS components Recall that classifying CIS into six components helps us know which parts to focus on when performing a given function. The Process Model (DFD) includes (a) people, (b) procedures, and (c) data from the Six CIS components [leaving hardware, networks, and software aside for now.] Abstractions and CIS Abstraction is a simplified description, view, or model of an object or system of objects. In a CIS: the process, data, object, and system models are abstractions of the computer information system. DFD Data Flow Diagram DFD is a picture of what people and procedures do to transform data into info DFD has four elements: 1. External entity: the original of data (source) or the receiver of information (sink) 2. Process: a series of steps that manipulate data 3. Data store: place to keep the data for later use 4. Data flow: describes the data and information elements passing between external entities, processes, and data stores. [know these] Graphing the DFD Symbol Sets Many symbol sets available! Gane-Sarson DFD Symbol Set: [3-3, chart7] How to Construct the DFD some rules

2 Systems Analysis Process Modeling (DFD) 2 of 10 Data flows must originate or terminate at a process Data stores must have at least one entry and one exit data flow Processes must have at least one entry and one exit data flow Bottom-Up DFD Creation Develop a narrative of the system Underline the action words Develop a sequential list of the action terms Eliminate tasks that do not transform the data Identify cohesive tasks Fit all the remaining tasks to a cohesive task Develop an IPO chart for each cohesive task Example: Part 1 Sometimes the office manager cannot determine whether the request is reasonable. When this happens, the request is forwarded to the owner, who makes this determination, contacts the customer if necessary, and either adjusts the request or rejects it outright. All requests are returned to the office manager for scheduling and filing. Example: Part 2 Action Word Task Number Task Description Submits none not identified Is forwarded none not identified Contacts #1 evaluate special requests Adjusts #1 evaluate special requests Rejects #1 evaluate special requests Are returned none not identified Consults #2 schedule charter Is reserved #2 schedule charter Checks #2 schedule charter Find #2 schedule charter Are entered #2 schedule charter Contacts #3 complete charter papers Finalize #3 complete charter papers Prepares #3 complete charter papers Signs #3 complete charter papers Example: Part 3 Input Processing Output Request contacts notation Adjusts Rejects

3 Systems Analysis Process Modeling (DFD) 3 of 10 Example: Part 4 Process Data Flow Process Data Flow Data Store Intake request evaluate special note charter requests Requests Top-Down DFD creation Get oral answers to the question What is the first task of this system? Continue with What happens next? Keep asking what happens next until the response is either We do it all over again or We re finished. Context Diagrams Show a single process Connected to the external entities Establishes the system boundaries. Example: A Time Card System Example: Revised Time Card System

4 Systems Analysis Process Modeling (DFD) 4 of 10 Level Decomposition Single process in the context diagram is composed of a collection of well-defined activities called cohesive tasks. Task definition begins by locating the events within a process. Events identify the end of one task and the beginning of another. Once a task is identified, the analyst can identify the inputs and outputs. Example: Level Decomposition Issue Access Cards INPUTS: class rosters (Source: Data Processing) access cards for registered students (Source: Data Processing) student registration (Source: Data Processing) signed non-piracy agreement (Source: Student) name on class rosters (Data Store: Roster) Issue Access Cards OUTPUTS: access cards (Sink: Student)

5 Systems Analysis Process Modeling (DFD) 5 of 10 lab handbook (Sink: Student) card numbers already issued (Sink: Data Processing) checkoff on class rosters (Data Store: Roster) new lab account (Data Store: Time) nonpiracy agreement (Data Store: Agreements) Logical and Physical DFDs Logical DFDs remove all reference to the implementation specifics of the system Physical DFDs specify the real world objects that are used to make the system work During the analysis phase: Develop the physical DFD Abstract the logical DFD During the design phase: Develop the logical DFD Develop the physical DFD TKSystem First-Level DFD

6 Systems Analysis Process Modeling (DFD) 6 of 10 Data Flow Walk-Thru

7 Systems Analysis Process Modeling (DFD) 7 of 10 TK System DFD Levels

8 Systems Analysis Process Modeling (DFD) 8 of 10 Class Project Discussion The analysis phase has started. Now you must understand more fully the existing system before a replacement system can be designed. The process model is the first abstraction to develop. Example: Existing System Context Diagram

9 Systems Analysis Process Modeling (DFD) 9 of 10 Example: Existing System First-Level DFD Class Project: Process Modeling Prepare the existing system context diagram and first level DFD Review the project management sections of Appendices A and B Develop the first draft of your week-by-week project budget Develop the first draft of your week-by-week project status Prepare a cover letter to transmit the budget and status reports to your client. Recap DFD models the processes of an information system DFDs consist of processes, external entities, data stores, and data flows DFD modeling begins with the context diagram, which depicts the entire system in a single process symbol surrounded by external entities. The first-level DFD (aka level-1) show the major functional components of the system as processes, connected by data flows to external entities, data stores, and other processes. As needed, you ll create successively more detailed levels to promote complete understand-

10 Systems Analysis Process Modeling (DFD) 10 of 10 ing of the system. [task] IPO Narrative: xxx Task: [task] Inputs: The item (Source: source name) Another item, and more (Data Store: staff) Outputs: Paycheck (Data Store: staff) Mailing labels (Sink: staff) Newsletter (Sink: staff) /Users/gbenoit/Documents/LIS486 - Systems Analysis/Spring2013/Analysis-DFD-003.rtf 12/30/12 6:34 PM

Topic # 08. Structuring System Process Requirements. CIS Life Cycle and Requirements Structuring Stage

Topic # 08. Structuring System Process Requirements. CIS Life Cycle and Requirements Structuring Stage Topic # 08 Structuring System Process Requirements CIS Life Cycle and Requirements Structuring Stage Objectives 1. Data Flow Diagrams 2. Rules and Guidelines to DFD development that lead to accurate and