1. IFS310: Week 3 BIS310: Structured Analysis and Design 5/4/2015 Process Modeling and Data Flow Diagrams

2. IFS310: Week 3 5/4/2015 Overview Discussion –Systems Theory (Input-Process-Output) –Process Modeling and Mechanics of DFDs –Current System Process Modeling –Future System Process Modeling

3. IFS310: Week 3 5/4/2015 Systems Theory and Process Concepts –A System is a Process The simplest process model of a system is based on inputs, outputs, and the system itself – viewed a process. The process symbol defines the boundary of the system. The system is inside the boundary; the environment is outside that boundary. The system exchanges inputs and outputs with its environment

4. IFS310: Week 3 5/4/2015

5. IFS310: Week 3 5/4/2015 System Models Logical models show what a system ‘is’ or ‘does’. They are implementation-independent; that is, they depict the system independent of any technical implementation. As such, logical models illustrate the essence of the system. Popular synonyms include essential model, conceptual model, and business model. Physical models show not only what a system ‘is’ or ‘does’, but also how the system is physically and technically implemented. They are implementation-dependent because they reflect technology choices, and the limitations of those technology choices. Synonyms include implementation model and technical model

6. IFS310: Week 3 5/4/2015 What is Process Modeling? Process modeling is a technique for organizing and documenting the structure and flow of data through a system’s PROCESSES and/or the logic, policies, and procedures to be implemented by a system’s PROCESSES. Process modeling originated in classical software engineering methods. A systems analysis process model consists of data flow diagrams (DFDs). –A data flow diagram (DFD) is a tool that depicts the flow of data through a system and the work or processing performed by that system. Synonyms include bubble chart, transformation graph, and process model.

7. IFS310: Week 3 5/4/2015 Data Flow Diagram There are only three symbols and one connection: processes –The rounded rectangles represent processes or work to be done. external agents –The squares represent external agents – the boundary of the system. data stores –The open-ended boxes represent data stores, sometimes called files or databases, and correspond to all instances of a single entity in a data model. data flows –The arrows represent data flows, or inputs and outputs, to and from the processes.

8. IFS310: Week 3 5/4/2015 Logical Processes You should be left only with logical processes that: –Perform computations (e.g., calculate grade point average) –Make decisions (determine availability of ordered products) –Sort, filter or otherwise summarize data (identify overdue invoices) –Organize data into useful information (e.g., generate a report or answer a question) –Trigger other processes (e.g., turn on the furnace or instruct a robot) –Use stored data (create, read, update or delete a record) Gane & Sarson Process Shape Process Name

9. IFS310: Week 3 5/4/2015 Data Flows –Data in Motion A data flow is data in motion. –A data flow represents an input of data to a process, or the output of data (or information) from a process. A data flow is also used to represent the creation, deletion, or update of data in a file or database (called a data store on the DFD). –A data flow is depicted as a solid-line with arrow. Gane & Sarson Data Flow Shape Name of data-flow

10. IFS310: Week 3 5/4/2015 External Agents –An external agent defines a person, organization unit, other system, or other organization that lies outside of the scope of the project, but which interacts with the system being studied. External agents provide the net inputs into a system, and receive net outputs from a system. Common synonyms include external entity. Gane & Sarson External Agent Shape System Concepts for Process Modeling External Agent

11. IFS310: Week 3 5/4/2015 System Concepts for Process Modeling Data Stores –A data store is an ``inventory’’ of data. Synonyms include file and database (although those terms are too implementation-oriented for essential process modeling). Gane & Sarson Data Store Shape D1 Data-store name

12. IFS310: Week 3 5/4/2015 Data Flow Diagramming Definitions Context Diagram –A data flow diagram (DFD) of the scope of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the system Level-0 Diagram –A data flow diagram (DFD) that represents a system’s major processes, data flows and data stores at a high level of detail

13. IFS310: Week 3 5/4/2015 Decomposition of DFDs Functional decomposition –Act of going from one single system to many component processes –Repetitive procedure Level-N Diagrams –A DFD that is the result of n nested decompositions of a series of subprocesses from a process on a level-0 diagram

14. IFS310: Week 3 5/4/2015 Guidelines for Drawing DFDs Completeness –DFD must include all components necessary for system –Each component must be fully described in the project dictionary or CASE repository Consistency –The extent to which information contained on one level of a set of nested DFDs is also included on other levels

15. IFS310: Week 3 5/4/2015 Figure 3.2 An unbalanced set of data flow diagrams (a) Context diagram (b) Level-0 diagram

16. IFS310: Week 3 5/4/2015 Common Mechanical Errors

17. IFS310: Week 3 5/4/2015 Illegal Data Flows

18. IFS310: Week 3 5/4/2015 Logical Processes Logical processes are work or actions that must be performed no matter how you implement the system. –Even for the future system, at the definition phase, the process model should be logical. In the study phase, the current system was analyzed in three levels of models: –Context Diagram –System Diagram –Event Diagrams

19. IFS310: Week 3 5/4/2015 Context Diagram

20. IFS310: Week 3 5/4/2015 System Diagram

21. IFS310: Week 3 5/4/2015 Event (Child) Diagram(s)

22. IFS310: Week 3 5/4/2015 How to Model a New System Step 1: Identify the changes in functional requirements for the new system Step 2: Establish the context for the new system Step 3: Create a new system diagram Step 4: Create necessary child diagrams

23. IFS310: Week 3 5/4/2015 Identify the changes in functional requirements for the new system Source: Problem Statement (Cause/Effect) Prioritize the “System Objectives” based on the urgency/importance of the effects Regroup the objectives into changes in functional requirements e.g., –Operational requirements, –Reporting/Inquiry requirements

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25. IFS310: Week 3 5/4/2015 Establish the context for the new system Analyze the new functional requirements in terms of necessary input/output of data i.e., Is there any new input? Is it necessary to produce new output? Is it going to allow new functions to external entities?

26. IFS310: Week 3 5/4/2015 New Context Diagram

27. IFS310: Week 3 5/4/2015 Create a new system diagram Principles for creating new DFD –Keep the model simple –Try to use data stores to connect all the processes Identify the functions that must be affected by the new functional requirements Determine the boundary of the new system

28. IFS310: Week 3 5/4/2015 New System Diagram

29. IFS310: Week 3 5/4/2015 Create necessary child diagrams Explode each function to depict the flow of data within the function A list of events within the function will be helpful Add necessary data stores

30. IFS310: Week 3 5/4/2015 A New Event (Child) Diagram

31. IFS310: Week 3 5/4/2015 Group Project (Assignment 2) Objectives –The goal for this assignment is having all leveled data flow diagrams (logical). Do your best to decompose the system (process) into as detail as you can, using assumptions from your common sense to the wildest imagination. You may use Visio, or any other graphical processors (e.g., Word, or PowerPoint) to create the diagrams.