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SDLC Phase II: Structuring System Requirements

SDLC Phase II: Structuring System Requirements. IS 582 Dr. Dania Bilal Spring 2007. Last Week: SDLC Phase II. Determining user requirements Structuring RFP based on gathered specifications of user needs Wrote specifications for certain functions Presented written specifications in class.

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SDLC Phase II: Structuring System Requirements

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  1. SDLC Phase II: Structuring System Requirements IS 582 Dr. Dania Bilal Spring 2007

  2. Last Week: SDLC Phase II • Determining user requirements • Structuring RFP based on gathered specifications of user needs • Wrote specifications for certain functions • Presented written specifications in class

  3. This Week: SDLC Phase II continued • Structuring system 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 • Refers 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

  16. DFDs • New physical • Depicts physical implementation of the new system • Examples • Visit • http://www.umsl.edu/~sauter/analysis/dfd/dfd.htm

  17. Collection Preparationis on a different set of slides

  18. Class Activity • Do a Level 0 DFD for an automation function and its tasks, using the various symbols. • Do a Level N DFD based on Level 0 • Use PPT to draw the final DFDs You may work in a group or individually.

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