IT 352: Systems Analysis & Design Chapter 3

IT 352: Information Systems Analysis and Design

• Course taught by Haifa Alhasson in 2020
• Based on chapter 3 and 2 from a Prentice Hall textbook, copyrighted 2011

Brief List of Topics

• Overview of Information System development environment
• Origin of Software
• Managing Information Systems Projects
• Identifying and Selecting Systems Development Projects
• Initiating and Planning Systems Development Projects
• System Requirements Determination
• Structuring System Process Requirements
• Designing Information Systems
• System Implementation
• Maintaining Information Systems

Modern Systems Analysis and Design (Chapter 7)

• Focuses on structuring system process requirements
• Explores data flow diagrams (DFDs)

Learning Objectives

• Understand the logical modeling of processes using DFD examples
• Create accurate and well-structured process models using DFDs following specific rules and guidelines
• Decompose DFDs into lower-level diagrams
• Balance higher-level and lower-level DFDs
• Use DFDs to analyze information systems
• Apply process modeling to electronic commerce applications
• Use decision tables for conditional statements

Process Modeling

• A graphical representation of capturing, manipulating, storing, and distributing data within a system and its environment, and among components.
• Included on the system development life cycle with the analysis phase highlighted
• Utilizes information gathered during requirements determination.
• Represents processes and data structures.
• Contains specific examples relating to a food order system (Hoosier Burger)

Deliverables and Outcomes

• Context Data Flow Diagram (DFD) including scope of system, or the current physical/logical system(adequate or sufficient detail only).
• Enables analysts to understand the current system.
• DFDs used to show a new logical system that is technology-independent and shows data flows, structure, and functional requirements.
• Each DFD component is thoroughly described.

Data Flow Diagramming Mechanics

• Represents physical and logical information systems
• Utilizes only four symbols for data flow
• Useful for depicting purely logical information flows.
• DFDs detailing physical systems differ from system flowcharts as they depict details of physical computing equipment

Definitions and Symbols

• Process: Work or actions performed on data (within the system)
• Data Store: Data at rest (within the system) for the data flow
• Source/Sink: External entity acting as an origin or destination of data (outside the system)
• Data Flow: Arrows depicting the movement of data

Developing DFDS

• Context Diagram: An overview of an organizational system including system boundaries, external entities interacting with the system, and major flows between entities and the system.
• Only one process symbol, no data stores as part of the context view
• Level-0 Diagram: Represents major processes, data flows, and data stores in a system with high level of detail
• Labels for processes are 1.0, 2.0, 3.0, and so on

Data Flow Diagramming Rules

• Inputs/Outputs to process must be different
• The process purpose is to transform inputs into outputs
• Every object in the DFD has a unique name for each process/data store
• Rules on data store movement, between processes and sources/sinks
• Direction of data flow and use of packages when data flows follow one path
• Rules for data flow between symbols, how they can flow in both directions
• How to handle data flows in two or more processes and use data stores

Decomposition of DFDs

• An iterative process of breaking a system description down into finer detail

• Creates a set of charts (explanation of one process's detail on another chart).

• Level-0 DFDS: are a high level diagram of the system's processes, which are given a unique label

• Level-1DFD: Breaks one of the Level-0 processes down further into more primitive, lower-level sub-processes

• Level-nDFD : Further breaking down a process in level-1 DFD into even more primitive or lowest levels

Balancing DFDS

• Conservation Principle: Preserves inputs and outputs of a process when doing next level decompositions (and also within the DFD diagram for a process)
• Balanced: When the input/output count of lower-level DFD process is the same as that of its higher-level equivalent process
• Data Flow Splitting: A composite data flow in a higher level would result in different parts going to different lower-level processes, which keeps the Diagram balanced
• Rules to govern drawing DFDs. Q, R, S, T rules as well as examples in a table (and illustrations on slides 33/34)

Four Different Types of DFDs

• Current Physical: Describes how the system works, identifies technology/people used, and the actual media for data flows and data stores.
• Current Logical: Describes what the system does. Removes physical aspects and reduces to data and processes that transform them.
• New Logical: Includes additional functions and removes/reorganizes data flows using DFDs.
• New Physical: Shows the physical implementation of the new system

Guidelines for Drawing DFDS

• Completeness: DFD must contain all components. Each is fully described in the dictionary or CASE repository (e.g., project documentation).
• Consistency: The extent to which information at one DFD level is also included in other levels (checking for inconsistencies).
• Timing: Not explicitly shown on DFDs
• Iterative Development: Analyst should expect to redraw the diagrams to achieve the desired system.
• Primitive DFD: lowest level of decomposition (as determined by analyst)

Using DFDS as Analysis Tools

• DFDs can be used for gap analysis (to discover discrepancies between multiple diagrams or within one).
• Identifying inefficiencies through a DFD (and application to business process re-engineering-BPR)

Modeling Logic with Decision Tables

• Matrix representation of logic for a decision, specifying possible conditions and actions.
• Effective for complex decision logic
• Condition stubs: lists conditions applicable to the decision
• Action stubs: lists actions for given conditions
• Rules: specifies actions based on conditions

Electronic Commerce Application: Process Modeling

• Completed JAD session for Pine Valley Furniture's Webstore, using data flow diagrams
• Identified six high-level processes
• The Process Modeling demonstrates translating the e-commerce system into Data Flow Diagrams to illustrate its structure.
• The Table shows how these processes connect in the Webstore (using a table 7-4) and illustrates further detail using a Level-0 diagram (using Figure 7-22)