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Chapter 6: The Traditional Approach to Requirements

Where You Are Headed?. Objectives. Explain how the traditional approach and the object-oriented approach differ when an event occursList the components of a traditional system and the symbols representing them on a data flow diagramDescribe how data flow diagrams can show the system at various levels of abstraction.

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Chapter 6: The Traditional Approach to Requirements

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    1. Chapter 6: The Traditional Approach to Requirements

    2. Where You Are Headed?

    3. Objectives Explain how the traditional approach and the object-oriented approach differ when an event occurs List the components of a traditional system and the symbols representing them on a data flow diagram Describe how data flow diagrams can show the system at various levels of abstraction

    4. Traditional versus OO Approaches

    5. Data Flow Diagrams Graphical system model that depicts process-oriented requirements for an IS Inputs / outputs Processes Data storage Easy to read and understand Answers the question: what does the system do in response to an event?

    6. Data Flow Diagram Symbols

    7. Data Flow Rules No additional notesNo additional notes

    10. DFDs and Decomposition A complex system is too difficult to understand as a whole (as a single process). To address, we break a system down to its component parts. Decomposition is the act of breaking a system into its component subsystems, processes, and subprocesses. Decompose until we have full understanding of requirements We use DFDs to decompose the system into its component parts.

    12. Decomposition Example

    13. Context Diagrams DFD that summarizes all processing activity Highest level view of system Shows system boundaries Scope is represented by a single process and outside agents When a system needs to respond to many events, often broken into subsystems:

    15. DFD Fragments Grouped by subsystem Represents system response to one event within a single process symbol Self contained model Focuses attention on single part of system Shows only data stores required to respond to events

    17. Decomposing DFD Fragments Sometimes DFD fragments need to be explored in more detail Broken into subprocesses with additional detail Goal: define all Elementary Processes for system May be DFD fragment level for simple events, sub-processes for complex events May be layers of sub-processes for very complex events Each Elementary Process should perform one logical task, made up of one or more of the following: Perform computations Make Decisions Sort, filter, summarize data Organize data (e.g., reporting) Trigger other processes Manipulate stored data (CRUD)

    19. Diagram 0 Model Combines all processes, data flows, data stores and external entities associated with all fragments within a system or subsystem on one diagram Decomposition of the context level diagram Useful during database design Can be confusing due to complexity

    21. Process View of DFD Creation In Planning phase: Define problem model boundaries with a context diagram In Analysis phase: Gather information to define events (event table) Define ERD Define DFD fragments (level 1) one per event Define Subprocesses for each fragment as required to get full understanding of requirements ITERATE If required, assemble fragments into Diagram 0

    22. Exercise Create DFD fragments for the following events and ERD:

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