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Structuring User Requirements

Structuring User Requirements. IS 592 Dr. Dania Bilal Spring 2005. Recap of Systems Analysis Phase. Determining user requirements Structuring user requirements Selecting the best system design strategy. Structuring User Requirements. Data Flow Diagrams (DFDs)

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Structuring User Requirements

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  1. Structuring User Requirements IS 592 Dr. Dania Bilal Spring 2005

  2. Recap of Systems Analysis Phase • Determining user requirements • Structuring user requirements • Selecting the best system design strategy

  3. Structuring User Requirements • Data Flow Diagrams (DFDs) • Analysis tool to structure user requirements in a system • Graphically represents data movement or flow in an information system and relationships among data flow

  4. DFDs • Show the processes that transform or change data • Focus on movement of data between processes ->DFDs are called process models • Process modeling shows data flow through the system based on an organization’s rules, decisions, and policies

  5. DFDs • Increase software development productivity by • avoiding mistakes in representing user requirements • Saving money in software cost • Based on user requirements gathered during planning stage • Evolve from the more general to the more specific

  6. DFDs • DFDs of current system • Used to understand current system • DFDs of new logical system • Used to show data flow, structure, and functional requirements of new system

  7. DFDs Symbols • Flow of data is represented by • Data flow • Data Store • Process • Source (external entities)

  8. DFDs Symbols • Data Flow • Data in motion from one place in a system to another • Example: user query in a database

  9. DFDs Symbols • Data store • Physical location or various locations of data in an information system • Example: a data store in a circulation system contains data about students, faculty, staff, community users, etc.

  10. DFDs Symbols • Process • Actions performed on data for transformation, storage, and distribution • May represent data in • File folder, computer-based file, notebook

  11. DFDs Symbols • Source/sink • Depicts the origin and/or destination of data • Referred to a external entity • Another organization or unit that sends and receives information from the system • A person who interacts with the system, inside or outside • Another information system that exchanges information with the system under analysis

  12. DFDs Symbols • Source/sink • Defines the system boundaries • Data originates outside a system from one or more sources, and the system produces information to one or more sinks

  13. DFD Mechanics • How the four symbols are represented? • Data flow: drawn as an arrow • Data store: drawn as a rectangular • Process: drawn as a circle • Source/sink: drawn as a square

  14. DFD Definitions • Level-0 diagram • Represents a system’s major processes, data flow, and data stores at the highest level of detail • Context diagram • Shows major flow between entities and the system (too general) • Level-N diagram • A DFD that results from a decomposed Level-0 diagram

  15. Types of DFDs • Current logical • Depicts current system • New logical • Has additional functions • Inefficient data flows are reorganized • New physical • Depicts physical implementation of the new system

  16. DFDs • Examples • Visit • http://www.umsl.edu/~sauter/analysis/dfd/dfd.htm • For additional information or clarification • Visit • http://management.wcupa.edu/mis451/chapter08.ppt#256,1,Slide 1

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