Process Modeling Fundamentals

Three Ways to Understand a System By its processes What are the systems main processes? What are the systems main processes? By its data What data does the system maintain? What data does the system maintain? By its output What output will the system produce? What output will the system produce? All 3 should be consistent with each other.

When is Process Modeling done? Process Modeling is part of the requirements Structuring Stage. We create process, logic and data models based on information gathered during the Requirements Determination stage (through interviews, surveys, etc.). In this way, requirements structuring helps guide us through determination, e.g. knowing what questions to ask in interviews.

Learning Objectives How to model organizational processes and the data they use, store and produce How to model organizational processes and the data they use, store and produce Understand rules and guidelines for drawing data flow diagrams Understand rules and guidelines for drawing data flow diagrams How to decompose data flow diagrams into lower-level diagrams How to decompose data flow diagrams into lower-level diagrams Rules of balancing data flow diagrams Rules of balancing data flow diagrams

Learning Objectives Explain the differences among four types of DFDs: current physical, current logical, new physical and new logical Explain the differences among four types of DFDs: current physical, current logical, new physical and new logical Discuss the use of data flow diagrams as analysis tools Discuss the use of data flow diagrams as analysis tools

What is Process Modeling? A way to graphically represent the system under study as processes that capture, manipulate, store and distribute data between a system and its environment and among system components There are many techniques that can be used for modeling processes Structured analysis and design models processes with data flow diagrams (DFDs) Structured analysis and design models processes with data flow diagrams (DFDs) Data flow diagrams are a way to graphically illustrate movement of data between external entities outside the system and the processes and data stores within a system

Process Modeling Some deliverables and outcomes for current and proposed system Context data flow diagram Context data flow diagram Logical DFDs Logical DFDs Level 0, level 1’s, etc. Technology independent Show data flows, structure and functional requirements of system Processing logic Processing logic Project dictionary and CASE repository Project dictionary and CASE repository

Four Types of Process Models CurrentProposed Logical Physical aspects of system are removed as much as possible Current system is reduced to data and processes that transform them Includes additional functions Obsolete functions are removed Inefficient data flows are reorganized Physical Process label includes an identification of the technology (people or systems) used to process the data Data flows and data stores are labeled with the actual name of the physical media on which data flow or in which data are stored Represents the physical implementation of the new system

Guidelines for Drawing DFDs Completeness DFD must include all components necessary for system DFD must include all components necessary for system Each component must be fully described in the project dictionary or CASE repository Each component must be fully described in the project dictionary or CASE repositoryConsistency The extent to which information contained on one level of a set of nested DFDs is also included on other levels The extent to which information contained on one level of a set of nested DFDs is also included on other levels 8.9

Guidelines for Drawing DFDs Timing Time is not represented well on DFDs Time is not represented well on DFDs Best to draw DFDs as if the system has never started and will never stop. Best to draw DFDs as if the system has never started and will never stop. Iterative Development Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled 8.10

Guidelines for Drawing DFDs Primitive DFDs Lowest logical level of decomposition Lowest logical level of decomposition Decision has to be made when to stop decomposition Decision has to be made when to stop decomposition 8.11