LIM, MARYLYN GRACE C.

OOA

            Book: Systems Analysis and Design: an Active Approach

            Author: George M. Marakas

            Reference No.: QA

                                    76.9

                                    S88

                                    M37

                                    2001

Chapter 5: Modeling the Process & Logic

Quote: “I’m never content until I have constructed a mechanical model of the subject I’m studying. If I succeed in making one, I understand; otherwise I don’t.”

Review:

            As a system analyst, there are several tools used to clear the system requirements by representing them as a set of models. This chapter talks about one of the tools used by system analyst, the Data Flow Diagram (DFD). DFD is a logical process-modeling that is used to represent different processes and data flows associated with both the current and proposed system.

            In logical process modeling, models are simplified representations of reality. The physical model represents “how” something happens while the logical model tells “what” a does w/o any constrictions of how that might be accomplished. In system analysis, there are 3 benefits of using a logical modeling approach. First, logical models reduce the risk of missing important business requirements of the system. Second, it makes easier for the system analyst to communicate w/ end users & system stakeholders. Lastly, this reduces the biases associated w/ the way the current system is implemented.

            DFD has 4 requirements. These are data flow, data store, process & entity. Data flow represents data that is in motion. While the data store represents data at rest. A process can transform data into another form or creates a new data or assembles the data into a useful output. Lastly, an entity interacts w/ the system but resides outside the system boundary. Using these 4 components, a system analyst can represent a complex system & understand the details not only the objectives of the system but also they will understand the system’s capabilities of achieving it.

            A system analyst creates a DFD hierarchy so that they can understand the complexity of a system & analyze it from a different perspective. There are 3 levels of DFD hierarchy. First, context level diagram, this diagram identifies the system boundary & its relationship to any source that may interact w/ it. Second, level-0 DFD, this represents the major processes contained in the system, the sequence of processes, the data stores accessed by the processes & the sources that interact w/ the system. Lastly, level-1 to level-n DFD, this diagram is created when the level-0 diagram is already completed & verified to be an accurate representation of the system.

            Lastly, this chapter talks about the basic modeling. Logic modeling is used to model the sequential or temporal logic contained in the process. There are 4 common logic modeling tools use. These are structured English, the decision table, decision tree and state-transition diagram. First, the structured English uses action verbs & nouns phrases to describe logic sequence & events. Second, decision table, this is a diagram of all the logic & possible outcomes associated w/ the process. Third, the decision tree, this represents the logic in a manner that is like a tree trunk & its branches lying on its side. Lastly, the state-transition diagram, this is useful  for modeling logic that is time-dependent or temporal.