Systems Analysis and Design - Chapter 5 questions and answers.

what is a process model? is a graphical way of representing how a business system should operate. It illustrates the processes or activities that are performed and how data move among them what is data flow diagramming? (DFD) is a technique that diagrams the business processes and the data that pass among them. The focus is mostly on the processes or activities that are performed What are logical process models? models that decribe a process, without suggesting how they are conducted what is a physical process model? provide information that is needed to build the system process is an acitvity or a function performed for some specific reason data flow a data flow is a single piece of data, or a logical collection of several pieces of information data store is a collection of data that is stored in some way external entity is a person, org,unit, or system that is external to the system but still interacts with it Decomposition breaking down DFDs to individual DFDs for further detail Context Diagram it shows the entire system as one process Level 0 Diagram showws all the major high level processes of the system and how they are interrelated. A process model has one and only one level 0 DFD Balancing ensuring that all information presented in a DFD at one level is accurately represented in the next-level DFD Level 1 Diagrams Each process of level 0 is decomposed into more explicit DFD called LEvel 1 How many level 1 diagrams should there be? as many processes as you have in level 0 Level 2 Diagrams the next level of decomposition- shows all the processes, data flows, and data stores that comprise a single process on the level 1 Diagram. Alternative Data Flows when a process produce data that flows under a different circumstance Process decsription used to explain why alternative data flows are different What are the 3 techniques used to describe processing logic - structured english - decision trees - decision tables Creating DFDs use info in use cases and requirements definition. the project team takes the use cases and rewrites the use cases, following the formal rules and syntax Creating Context Diagram Draw one process symbol numbered 0 add all inputs and outputs on form as data flows draw the external entities NO DATA STORES Creating DFD Fragments fragment is one part of a DFD that eventually will be combined with other DFD fragments for form a DFD each use case is converted into one DFD fragement Creatine level 0 DFD combine the set of DFD fragments into one diagram reads from left to right Iteration is the cornerstone of a good DFD Level 1 DFD a DFD is created for each process in LEVEL 0 Validating the DFD Syntax Errors: can be though of as grammatical errors that violate the rules of the DFD language