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Structuring System Requirements IS 582 Dr. Dania Bilal Spring 2006 Recap of Systems Analysis Phase Determining user requirements Structuring user requirements Selecting the best system design strategy 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 Example: user query in a database 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, computer-based file, 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 the 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 Context diagram Represents a system’s major processes, data flow, and data stores at the highest level of detail 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 http://www.umsl.edu/~sauter/analysis/dfd/dfd.htm Class Activity Do a DFD for an automation function and its tasks. Since we don’t have Visio or the like software, use PPT. (You will work on this as time permits).