10 Systems Analysis and Design in a

10

Systems Analysis and Design in a Changing World, Fourth Edition 10

Learning Objectives 10 u Describe the steps involved in the traditional approach to designing the application architecture u Develop a system flowchart u Develop a structure chart using transaction analysis and transform analysis u Write pseudocode for structured modules u Explain how to use three-layer design with the traditional approach Systems Analysis and Design in a Changing World, 4 th Edition 3

10 Overview u Traditional approach to designing software l Overview of structured models, model development process, related terminology l How data flow diagrams are annotated with automation boundary information l How analysis phase models are transformed into design models using system flowcharts, structure charts, and module pseudocode l Integration into other design phase activities l Applying approach to a three-layer architecture Systems Analysis and Design in a Changing World, 4 th Edition 4

The Structured Approach to Designing the Application Architecture u Consists 10 of the application software programs l Designed in conjunction with database and user interface. l Module: Is small section of program code that carries out a single function. l Hierarchy of modules ( main or boss , control and leaf) l Computer Program: Set of modules that are compiled into a single executable entity l System flow chart: diagram describes the overall flow of control between computer in a system 5

The Structured Approach to Designing the Application Architecture (Cont. ) 10 u Design internal logic of individual modules (pseudocode) l Pseudocode: structured-programming –like statements that describe the logic of the module. u Analysts use top-down approach ( Data flow diagrams and documentations). l DFDs with automation boundaries ( Divides the computerized portions of the system from the manual portions). l System flowcharts, structure charts, pseudocode Systems Analysis and Design in a Changing World, 4 th Edition 6

Structured Design Models Systems Analysis and Design in a Changing World, 4 th Edition 10 7

10 The Automation System Boundary u Partitions data flow diagram processes into manual processes and automated systems u Processes can be inside ( online or batch) or outside boundary (manual process). u Data flows can be inside and outside of boundary l Data flows that cross system boundary represent inputs and outputs of system ( user interfaces). l Data flows that cross boundaries between programs represent program-to-program communication Systems Analysis and Design in a Changing World, 4 th Edition 8

DFD with Automation System Boundary 10 (Figure 10 -2) Systems Analysis and Design in a Changing World, 4 th Edition 9

10 The System Flowchart u Representation of various computer programs, files, databases, and associated manual processes that make up complete system u Frequently constructed during analysis activities u Graphically describes organization of subsystems into automated and manual components u Can show type of transaction processing system l Batch ( produce daily transaction file - process and update file). l Real-time ( transaction entered—DMS`s updated) Systems Analysis and Design in a Changing World, 4 th Edition 10

10 The System Flowchart (Cont. ) u Many business systems today have both real-time and batch components. l Credit card: purchases at least verified in real time and monthly account statements and customer payments typically are processed in batches. u System flow chart is used to describe the overall organization of this type of systems and show the relationship between the real-time components and the batch processing. Systems Analysis and Design in a Changing World, 4 th Edition 11

10 Common System Flowchart Symbols Systems Analysis and Design in a Changing World, 4 th Edition 12

Sample System Flowchart for Payroll System (Figure 10 -4) Systems Analysis and Design in a Changing World, 4 th Edition 10 13

System Flowchart for RMO (Figure 10 -5) Systems Analysis and Design in a Changing World, 4 th Edition 10 14

10 The Structure Chart u. A hierarchal diagram showing the relationships between the modules of a computer program. u Describes functions and subfunctions of each part of system u Higher-level module: are control modules that control the flow of execution. u Lower- level module: are “worker-bee” modules and contain the program logic to actually perform the functions. Systems Analysis and Design in a Changing World, 4 th Edition 15

10 The Structure Chart (Cont. ) u Program call: occurs when one module invokes a lower-level module to perform a needed service. u Data couples: the individual data items that are passed between modules in a program call. u Simple and direct organization l Each module performs a specific function l Each layer in a program performs specific activities u Chart is tree-like with root module and branches Systems Analysis and Design in a Changing World, 4 th Edition 16

A Simple Structure Chart for the Calculate Pay Amounts Module Systems Analysis and Design in a Changing World, 4 th Edition 10 17

Structure Chart Symbols Systems Analysis and Design in a Changing World, 4 th Edition 10 18

10 Structure Chart Symbols (Cont. ) u Part A: the rectangle represents a module. u Part B: the rectangle with the double bars represents module that is used in several places ( optional). u Part C: How data are passed between modules. l Arrow with the open circle ( data couple). l Arrow with the darkened circle (control couple flag): is purely internal information that is used between modules to indicate some result (eg. Record passing and validation test) Systems Analysis and Design in a Changing World, 4 th Edition 19

10 Structure Chart Symbols (Cont. ) u Part E: shows the notation used to indicate iteration through several modules. u Part F: shows conditional calling of low- level modules( the program calls modules only when certain conditions exist. Systems Analysis and Design in a Changing World, 4 th Edition 20

Structure Chart for Entire Payroll Program Systems Analysis and Design in a Changing World, 4 th Edition 10 21

10 Developing a Structure Chart u Transaction analysis l Uses system flow chart and event table inputs l Upper-level modules developed first l Identifies each transaction supported by program u Transform analysis l Uses DFD fragments for inputs l Computer program “transforms” inputs into outputs l Charts have input, calculate, and output subtrees Systems Analysis and Design in a Changing World, 4 th Edition 22

10 Event-partitioned DFD for the Order-Entry Subsystem (Figure 10 -9) Systems Analysis and Design in a Changing World, 4 th Edition 23

High-Level Structure Chart for the Order-Entry Subsystem After Transaction Analysis Systems Analysis and Design in a Changing World, 4 th Edition 10 24

Steps to Create a Structure Chart from a DFD Fragment u Determine l 10 primary information flow Main stream of data transformed from some input form to output form u Find process that represents most fundamental change from input to output u Redraw DFD with inputs to left and outputs to right – central transform process goes in middle u Generate first draft of structure chart based on redrawn data flow Systems Analysis and Design in a Changing World, 4 th Edition 25

10 The Create New Order DFD Fragment Systems Analysis and Design in a Changing World, 4 th Edition 26

Decomposed DFD for Create New Order Systems Analysis and Design in a Changing World, 4 th Edition 10 27

10 Rearranged Create New Order DFD Systems Analysis and Design in a Changing World, 4 th Edition 28

First Draft of the Structure Chart for Create New Order (Figure 10 -14) Systems Analysis and Design in a Changing World, 4 th Edition 10 29

Steps to Create a Structure Chart from a DFD Fragment (continued) u Add 10 other modules l Get input data via user-interface screens l Read from and write to data storage l Write output data or reports u Add logic from structured English or decision tables u Make final refinements to structure chart based on quality control concepts Systems Analysis and Design in a Changing World, 4 th Edition 30

The Structure Chart for the Create New Order Program (Figure 10 -15) Systems Analysis and Design in a Changing World, 4 th Edition 10 31

10 Combination of Structure Charts: Transaction and Transform Analysis (Figure 10 -16) Systems Analysis and Design in a Changing World, 4 th Edition 32

10 Evaluating the Quality of a Structure Chart u Module coupling l Measure of how module is connected to other modules in program l Goal is to be loosely coupled u Module cohesion l Measure of internal strength of module l Module performs one defined task l Goal is to be highly cohesive Systems Analysis and Design in a Changing World, 4 th Edition 33

Examples of Module Cohesion Systems Analysis and Design in a Changing World, 4 th Edition 10 34

10 Module Algorithm Design—Pseudocode u Describes internal logic of software modules u Variation of structured English that is closer to programming code u Syntax should mirror development language u Three types of control statements used in structured programming l Sequence – sequence of executable statements l Decision – if-then-else logic l Iteration – do-until or do-while Systems Analysis and Design in a Changing World, 4 th Edition 35

Module Algorithm Design—Pseudocode (Cont. ) 10 u. A simple example of the logic of the payroll system. u Payroll program Do. Until No more time cards Call Enter time cards Call Calculate amount Call output payroll End Until Systems Analysis and Design in a Changing World, 4 th Edition 36

Integrating Structured Application Design with Other Design Tasks 10 u Structure chart must be modified or enhanced to integrate design of user interface, database and network. l Are additional modules needed? l Does the pseudocode in modules need modification? l Are additional data couples needed to pass data? u Structure charts and system flowcharts must correspond to planned network architecture l Required protocols, capacity, and security 37

10 Three-Layer Design u Three-layer l architecture View layer, business logic layer, and data layer u Structure charts and system flowcharts describe design decisions and software structuring u Employs multiple programs for user interface, business logic, and data access modules u Modules in different layers communicate over real -time links using well-defined protocols Systems Analysis and Design in a Changing World, 4 th Edition 38

System Flowchart Showing Three-Layer Architecture for Customer Order Systems Analysis and Design in a Changing World, 4 th Edition 10 39

Structure Chart Showing Three-Layer Architecture for Create New Order (Figure 10 -20) Systems Analysis and Design in a Changing World, 4 th Edition 10 40

10 Summary u For traditional structured approach to systems design, primary input is data flow diagram l DFD is enhanced by adding system boundary l Designer describes processes within each DFD boundary using one or more structure charts u Structure charts developed using l Transaction analysis – multiple transaction types l Transform analysis – single transaction from input to output Systems Analysis and Design in a Changing World, 4 th Edition 41

10 Summary (continued) u Structure charts may be based on three-layer architecture l Modules will be clearly identified by layer l Structure chart may be decomposed if layers execute on multiple systems u Structured design may also include l System flowcharts to show data movement l Module pseudocode to describe internal logic of structure chart module Systems Analysis and Design in a Changing World, 4 th Edition 42