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/cha pter08.ppt#256,1,Slide 1