SDLC Phase II: Structuring System Requirements IS 582 Dr. Dania Bilal Spring 2008

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

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

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

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

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

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

DFDs Symbols Data Flow –Data in motion from one place in a system to another Examples –user query in a database –Other examples???

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.

DFDs Symbols Process –Actions performed on data for transformation, storage, and distribution –May represent data in File folder, notebook

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

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

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

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

Types of DFDs Current logical –Depicts current system New logical –Has additional functions –Inefficient data flows are reorganized

DFDs New physical –Depicts physical implementation of the new system Examples –Visit

Group or Individual Class Activity Do a Level 0 DFD for an automation function that is of interest to you using adequate symbols. You may use a drawing software to perform this activity. Do a Level N DFD based on Level 0 diagram