Systems Analysis and Design - Chapter 5

Systems Analysis and Design - Chapter 5 Process Model - Definition: A graphical representation of how a business system operates, illustrating the processes or activities performed and the flow of data among them. Data Flow Diagramming (DFD) - Definition: A technique used to visually diagram business processes and the data exchanged among them. The emphasis is on depicting the activities performed within the system. Logical vs. Physical Process Models - Logical Process Models: Describe processes without specifying how they are conducted. Focus on the what rather than the how. - Physical Process Model: Provide detailed information necessary for system development, illustrating how the process is implemented. Key Terms 1. Process: An activity or function carried out for a specific purpose. 2. Data Flow: A single piece of data or a logical collection of multiple pieces of information moving through the system. 3. Data Store: A collection of data stored in some form, such as a database. 4. External Entity: Individuals, organizations, or systems that interact with the system but are not part of it. 5. Decomposition: The breakdown of DFDs into smaller, more detailed DFDs to enhance clarity and understanding. DFD Types and Levels - Context Diagram: Represents the entire system as one process, showing external entities and their interactions without detailing internal processes. - Level 0 Diagram: Illustrates all major high-level processes of the system and how they relate to each other. Each system should have a single Level 0 DFD. - Balancing: The practice of ensuring that all information in one level's DFD accurately corresponds to its representation in the next level's DFD. - Level 1 Diagrams: Decomposes each Level 0 process into more detailed DFDs, demonstrating individual functions. The number of Level 1 diagrams should correspond to the number of processes at Level 0. - Level 2 Diagrams: Further breaks down a specific Level 1 process into its constituent processes, data flows, and data stores. Alternative Data Flows - Definition: Data flows produced by a process under different circumstances compared to the usual data flow. Process Description - Explains the reasons for differences between alternative data flows. Processing Logic Techniques Three common techniques for describing processing logic are: 1. Structured English: A method of writing specifications in a clear, unambiguous way using straightforward language. 2. Decision Trees: Visual representations that map out decision processes and their potential outcomes. 3. Decision Tables: A tabular method for representing combinations of conditions and corresponding actions or outcomes. Creating DFDs To create DFDs, utilize information gathered from: - Use cases and requirements definitions. - Rewrite use cases following formal DFD syntax and rules. Steps for Creating DFDs 1. Creating the Context Diagram: - Draw a single process symbol labeled as "0".