Systems Analysis and Design in a Changing World

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Systems Analysis and Design in a Changing World, Fourth Edition 6

Systems Analysis and Design in a Changing World, Fourth Edition 6

6 Learning Objectives u Explain how the traditional approach and the object-oriented approach differ

6 Learning Objectives u Explain how the traditional approach and the object-oriented approach differ when modeling the details of a use case 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 Systems Analysis and Design in a Changing World, 4 th Edition 2

6 Learning Objectives (continued) u Develop data flow diagrams, data element definitions, data store

6 Learning Objectives (continued) u Develop data flow diagrams, data element definitions, data store definitions, and process descriptions u Read and interpret Information Engineering models that can be incorporated within traditional structured analysis u Develop tables to show the distribution of processing and data access across system locations Systems Analysis and Design in a Changing World, 4 th Edition 3

6 Overview u What the system does and what event occurs – activities and

6 Overview u What the system does and what event occurs – activities and interactions (use case) u Traditional structured approach to representing activities and interactions u Diagrams approach and other models of the traditional u RMO customer support system example shows how each model is related u How traditional and IE approaches and models can be used together to describe system Systems Analysis and Design in a Changing World, 4 th Edition 4

Traditional versus Object-Oriented Approaches Systems Analysis and Design in a Changing World, 4 th

Traditional versus Object-Oriented Approaches Systems Analysis and Design in a Changing World, 4 th Edition 6 5

Traditional Approach in this Chapter Systems Analysis and Design in a Changing World, 4

Traditional Approach in this Chapter Systems Analysis and Design in a Changing World, 4 th Edition 6 6

6 Data Flow Diagrams (DFDs) u Graphical system model that shows all main requirements

6 Data Flow Diagrams (DFDs) u Graphical system model that shows all main requirements for an IS in one diagram l Inputs/outputs l Processes l Data storage u Easy to read and understand with minimal training Systems Analysis and Design in a Changing World, 4 th Edition 7

6 Data Flow Diagram Symbols (Figure 6 -3) Systems Analysis and Design in a

6 Data Flow Diagram Symbols (Figure 6 -3) Systems Analysis and Design in a Changing World, 4 th Edition 8

DFD Fragment Showing Use Case Look up item availability from the RMO (Figure 6

DFD Fragment Showing Use Case Look up item availability from the RMO (Figure 6 -4) Systems Analysis and Design in a Changing World, 4 th Edition 6 9

6 DFD and Levels of Abstraction u Data flow diagrams (DFDs) are decomposed into

6 DFD and Levels of Abstraction u Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail u Higher-level diagrams provide general views of system u Lower-level diagrams provide detailed views of system u Differing views are called levels of abstraction Systems Analysis and Design in a Changing World, 4 th Edition 10

6 Layers of DFD Abstraction for Course Registration System (Figure 6 -6) Systems Analysis

6 Layers of DFD Abstraction for Course Registration System (Figure 6 -6) Systems Analysis and Design in a Changing World, 4 th Edition 11

6 DFD and Levels of Abstraction u. A System Context Diagram (SCD) in software

6 DFD and Levels of Abstraction u. A System Context Diagram (SCD) in software engineering is a diagram that defines the boundary between the system, or part of a system, and its environment, showing the entities that interact with it. This diagram is a high level view of a system. Systems Analysis and Design in a Changing World, 4 th Edition 12

6 Context Diagrams u DFD that summarizes all processing activity for the system or

6 Context Diagrams u DFD that summarizes all processing activity for the system or subsystem u Highest u Shows level (most abstract) view of system boundaries u System scope is represented by a single process, external agents, and all data flows into and out of the system Systems Analysis and Design in a Changing World, 4 th Edition 13

6 DFD Fragments u Created for each use case in the event table u

6 DFD Fragments u Created for each use case in the event table u Represent system response to one event within a single process symbol u Self-contained models u Focus attention on single part of system u Show only data stores required in the use case Systems Analysis and Design in a Changing World, 4 th Edition 14

Automation System Boundary 6 Chapter 5

Automation System Boundary 6 Chapter 5

Context Diagram for RMO Order-Entry Subsystem (Figure 6 -11) Systems Analysis and Design in

Context Diagram for RMO Order-Entry Subsystem (Figure 6 -11) Systems Analysis and Design in a Changing World, 4 th Edition 6 16

Five Separate DFD Fragments for RMO Order-Entry Subsystem (Figure 6 -12) Systems Analysis and

Five Separate DFD Fragments for RMO Order-Entry Subsystem (Figure 6 -12) Systems Analysis and Design in a Changing World, 4 th Edition 6 17

6 Structured English u Method of writing process specifications u Combines structured programming techniques

6 Structured English u Method of writing process specifications u Combines structured programming techniques with narrative English u Well-suited for lengthy sequential processes or simple control logic (single loop or if-then-else) u Ill-suited for complex decision logic or few (or no) sequential processing steps Systems Analysis and Design in a Changing World, 4 th Edition 18

Process 2. 1 and Structured English Process Description (Figure 6 -21) Systems Analysis and

Process 2. 1 and Structured English Process Description (Figure 6 -21) Systems Analysis and Design in a Changing World, 4 th Edition 6 19

6 Decision Tables and Decision Trees u Can summarize complex decision logic better than

6 Decision Tables and Decision Trees u Can summarize complex decision logic better than structured English u Incorporate logic into the table or tree structure to make descriptions more readable Systems Analysis and Design in a Changing World, 4 th Edition 20

Decision Tree for Calculating Shipping Charges (Figure 6 -24) Systems Analysis and Design in

Decision Tree for Calculating Shipping Charges (Figure 6 -24) Systems Analysis and Design in a Changing World, 4 th Edition 6 21

6 Data Flow Definitions u Textual description of data flow’s content and internal structure

6 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 plus computed values u Algebraic notion describes data elements on data flow plus data structure Systems Analysis and Design in a Changing World, 4 th Edition 22

Data Flow Definition for RMO Products and Items Control Break Report (Figure 6 -29)

Data Flow Definition for RMO Products and Items Control Break Report (Figure 6 -29) Systems Analysis and Design in a Changing World, 4 th Edition 6 23

6 Data Element Definitions u Data type description l String, integer, floating point, Boolean

6 Data Element Definitions u Data type description l String, integer, floating point, Boolean l Sometimes very specific written description u Length of element u Maximum and minimum values u Data dictionary – repository for definitions of data flows, data stores, and data elements Systems Analysis and Design in a Changing World, 4 th Edition 24

Data Element Definition Examples 6 (Figure 6 -30) Systems Analysis and Design in a

Data Element Definition Examples 6 (Figure 6 -30) Systems Analysis and Design in a Changing World, 4 th Edition 25

Components of a Traditional Analysis Model 6 (Figure 6 -31) Systems Analysis and Design

Components of a Traditional Analysis Model 6 (Figure 6 -31) Systems Analysis and Design in a Changing World, 4 th Edition 26

6 Summary u Data flow diagrams (DFDs) are used in combination with event table

6 Summary u Data flow diagrams (DFDs) are used in combination with event table and entity-relationship diagram (ERD) to model system requirements u DFDs model system as set of processes, data flows, external agents, and data stores u DFDs easy to read – graphically represent key features of system using small set of symbols u Many types of DFDs – context diagrams, DFD fragments, subsystem DFDs, event-partitioned DFDs, and detailed process DFDs Systems Analysis and Design in a Changing World, 4 th Edition 27

6 Summary (continued) u Each process, data flow, and data store requires detailed definition

6 Summary (continued) u Each process, data flow, and data store requires detailed definition u Analyst may define processes as structured English process specifications, decision tables, decision trees, or detail process DFDs u Detailed process decomposition DFDs used when internal process complexity is great u Data flows are defined by component data elements and their internal structure (algebraic notation) Systems Analysis and Design in a Changing World, 4 th Edition 28