1 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Chapter 6 The Traditional Approach to Requirements

2 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Objectives u Explain how the traditional approach and the object-oriented approach differ when an event occurs u List the components of a traditional system and the symbols representing them on a data flow diagram u Describe how data flow diagrams can show the system at various levels of abstraction

3 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Objectives u Develop data flow diagrams, data element definitions, data store definitions, and process descriptions u Develop tables to show the distribution of processing and data access across system locations u Read and interpret information engineering models that can be incorporated within traditional structured analysis

4 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Traditional versus OO Approaches Figure 6-1

5 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Data Flow Diagrams u Graphical system model that shows all main requirements for an IS l Inputs / outputs l Processes l Data storage u Easy to read and understand

6 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Data Flow Diagram Symbols Figure 6-2 Process Step-by-step instructions Data flow External agent Data store Data at rest Real-time link

7 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd DFD Fragment from the RMO Case Figure 6-3

8 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd DFD Integrates Event Table and ERD Figure 6-4

9 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd DFD and Levels of Abstraction u DFDs are decomposed into additional diagrams to provide multiple levels of detail u Higher levels are more general u Lower levels are more detailed

10 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Layers of DFD Abstraction Figure 6-5

11 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Context Diagram Faculty Member Academic Department Student Course Registration System Schedule Data Enrollment Request Schedule Class List

12 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd DFD Fragments Schedule Course Academic Department Schedule data Enroll Student Course enrollmentOffered Course Schedule Enrollment Request Student List Offered CourseCourse enrollmentOffered Course Student List Produce Class List Faculty Member Class List

13 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Diagram 0 Produce Class List Enroll Student Schedule Course Academic Department Faculty Member Student Course enrollment Offered Course Student List Class List Schedule Enrollment Request Schedule data 2 13

14 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Context Diagrams u DFD that summarizes all processing activity u Highest level view of system u Shows system boundaries u Scope is represented by a single process and outside agents

15 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd DFD Fragments u Represents system response to one event within a single process symbol u Self contained model u Focuses attention on single part of system u Shows only data stores required to respond to events

16 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Context Diagram for RMO Order-Entry Subsystem Figure 6-8

17 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Two DFD Fragments for RMO Order-Entry System Figure 6-10

18 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Event Partitioned System Model u DFD that models system requirements using a single process for each event in a system or subsystem u Sometimes called diagram 0 u Decomposition of the context level diagram u Is decomposed into more detailed DFD fragments

19 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Combining DFD Fragments Figure 6-11

20 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Decomposing DFD Fragments u Sometimes DFD fragments need to be explored in more detail u Broken into subprocesses with additional detail u Numbering scheme doesn’t equate to execution sequence

21 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Detailed Diagram for Create New Order Figure 6-13

22 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Physical and Logical DFDs u Logical model l Assumes implementation in perfect technology l Does not tell how system is implemented u Physical model l Describes assumptions about implementation technology l Developed in last stages of analysis or in early design

23 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Evaluating DFD Quality u Readable u Internally consistent u Accurately represents system u Reduces information overload l Rule: 7 +/- 2 u Minimizes required number of interfaces

24 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Data Flow Consistency Problems u Differences in data flow content between a process and its process decomposition u Data outflows without corresponding inflows u Data inflows without corresponding outflows u Results in unbalanced DFDs

25 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Consistency Rules u All data that flows into a process must flow out or be used to generate data that flows out u All data that flows out of a process must have flowed in or been generated from data that flowed in

26 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Unnecessary Data Input: Black Hole Figure 6-15

27 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process with Impossible Data Output: Miracle Figure 6-16

28 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process with Unnecessary Data Input Figure 6-17

29 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process with Impossible Data Output Figure 6-18

30 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Documentation of DFD Components u Lowest level processes need to be described in detail u Data flow contents need to be described u Data stores need to be described in terms of data elements u Each data element needs to be described u Various options for process definition exist

31 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Structured English u Method of writing process specifications that combines structured programming techniques with narrative English l Well suited to lengthy sequential processes or simple control logic l Ill-suited for complex decision logic or few sequential processing steps

32 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process 2.1 and Structured English Process Description Figure 6-20

33 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Decision Tables and Decision Trees u Can summarize complex decision logic better than structured English u Incorporates logic into the table or tree structure to make descriptions more readable

34 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Data Flow Definitions u Textual description of data flow’s content and internal structure u Often coincide with attributes of data entities included in ERD Data Flow Definitions Simply Listing Elements Figure 6-25

35 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Data Element Definitions u Data type description l e.g. string, integer, floating point, Boolean l Very specific u Length of element u Maximum and minimum values

36 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Components of a Traditional Analysis Mode Figure 6-30

37 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Information Engineering Models u Focuses on strategic planning and data requirements of new system u Shares features with structured system development methodology u Developed by James Martin in early 1980’s

38 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Information Engineering System Development Life Cycle Phases Figure 6-31

39 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process Decomposition and Dependency Models u IE process model information types l Decomposition of processes into other processes l Dependency relationships among processes l Internal processing logic

40 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process Dependency Diagram Figure 6-34

41 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Process Dependency Diagram with Data Flows Figure 6-35

42 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Locations and Communication Through Networks u Logical information needed during analysis l Number of user locations l Processing and data access requirements at various locations l Volume and timing of processing and data access requests u First, identify locations where work is to be performed

43 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd RMO Location Diagram Figure 6-36

44 6 Systems Analysis and Design in a Changing World, 2 nd Edition, Satzinger, Jackson, & Burd Location Considered u List functions performed by users at each location l Place in matrix l Rows are system activities l Columns are locations u Other matrices l Activities versus data