Systems Analysis and Design in a Changing World, 6th Edition 1 Chapter 5.
Systems Analysis and Design in a Changing World, 6th Edition 1 Online Chapter B.
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Transcript of Systems Analysis and Design in a Changing World, 6th Edition 1 Online Chapter B.
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Systems Analysis and Design in a Changing World, 6th Edition 1
Online Chapter B
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The Traditional Approach to Requirements
Systems Analysis and Design in a Changing World 6th Ed
Satzinger, Jackson & Burd
Online Chapter B
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Systems Analysis and Design in a Changing World, 6th Edition 3
Online Chapter B Outline
Traditional and Object-Oriented Views of Activities and Use Cases
Data Flow Diagrams Documentation of DFD Components Locations and Communication through Networks
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Systems Analysis and Design in a Changing World, 6th Edition 4
Learning Objectives Explain how the traditional approach and the object-
oriented approach differ when modeling the details of a use case
List the components of a traditional system and the symbols representing them on a data flow diagram
Describe how data flow diagrams can show the system at various levels of abstraction
Develop data flow diagrams, data element definitions, data store definitions, and process descriptions
Develop tables to show the distribution of processing and data access across system locations
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Systems Analysis and Design in a Changing World, 6th Edition 5
Overview Chapters 3, 4, and 5 described two key concepts
associated with modeling functional requirements in the newer (OO) approaches to information systems development: the use cases and the domain classes involved in users’ work
This chapter describes an older and more traditional approach to representing requirements
Entity-relationship diagrams represent things in the user’s work domain
Data flow diagrams (DFDs) and associated concepts model system processes instead of use case diagrams and system sequence diagrams
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Systems Analysis and Design in a Changing World, 6th Edition 6
Traditional vs. OO Approach
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Systems Analysis and Design in a Changing World, 6th Edition 7
Requirements Models for Traditional vs. OO Approach
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Systems Analysis and Design in a Changing World, 6th Edition 8
Data Flow Diagram Symbols
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Systems Analysis and Design in a Changing World, 6th Edition 9
DFD for process Look up item availability
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Systems Analysis and Design in a Changing World, 6th Edition 10
DFD Decomposes
To show different levels of abstraction
Context DiagramDiagram 0Diagram 1
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Systems Analysis and Design in a Changing World, 6th Edition 11
DFD FragmentsOne for each use case
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Systems Analysis and Design in a Changing World, 6th Edition 12
Combine DFD Fragments
To Create Diagram 0
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Systems Analysis and Design in a Changing World, 6th Edition 13
RMO Data Flow Diagrams
Context Diagram
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Systems Analysis and Design in a Changing World, 6th Edition 14
RMO Subsystems and Use Cases
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Systems Analysis and Design in a Changing World, 6th Edition 15
Context Diagram for RMO Order Entry Subsystem
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Systems Analysis and Design in a Changing World, 6th Edition 16
DFD Fragments for RMO Order Entry Subsystem
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Systems Analysis and Design in a Changing World, 6th Edition 17
Diagram 0 for RMO Order Entry Subsystem
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Systems Analysis and Design in a Changing World, 6th Edition 18
Decomposing Process 2 from DFD Fragment 2
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Systems Analysis and Design in a Changing World, 6th Edition 19
Physical DFDs
Sometimes useful for modeling processes
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Systems Analysis and Design in a Changing World, 6th Edition 20
Evaluating DFD Quality
Minimize complexity Information overload – difficulty in understanding that
occurs when a reader receives too much information at one time
Rule of 7 ± 2 (Miller’s number) – the rule of model design that limits the number of model components or connections among components to no more than nine
Minimization of interfaces – a principle of model design that seeks simplicity by limiting the number of connections among model components
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Systems Analysis and Design in a Changing World, 6th Edition 21
Evaluating DFD Quality Ensuring Data Flow Consistency
Three Common Errors Differences in data flow content between a process and its
process decomposition Data outflows without corresponding data inflows Data inflows without corresponding outflows
Balancing – equivalence of data content between data flows entering and leaving a process and data flows entering and leaving a process decomposition DFD
Black hole – a process or data store with a data input that is never used to produce a data output
Miracle – a process or data store with a data element that is created out of nothing
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Systems Analysis and Design in a Changing World, 6th Edition 22
Process Descriptions
Structured English – a method of writing process specifications that combines structured programming techniques with narrative English
Decision table – a tabular representation of processing logic containing decision variables, decision variable values, and actions or formulas
Decision tree – a graphical description of process logic that uses lines organized like branches of a tree
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Systems Analysis and Design in a Changing World, 6th Edition 23
Structured English Example
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Systems Analysis and Design in a Changing World, 6th Edition 24
RMO Process 2.1 Structured English
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Systems Analysis and Design in a Changing World, 6th Edition 25
Structured English
to determine delivery charges
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Systems Analysis and Design in a Changing World, 6th Edition 26
Decision Table calculating shipping charges
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Systems Analysis and Design in a Changing World, 6th Edition 27
Decision Tree calculating shipping charges
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Systems Analysis and Design in a Changing World, 6th Edition 28
Decision Table with multiple action rows
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Systems Analysis and Design in a Changing World, 6th Edition 29
Data Flow Definitions Data flow definition – a textual description of a data
flow’s content and internal structure Can be simple list of data elements that make up the
data flow. For new order:
Can use an algebraic notation to indicate elements and structure
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Systems Analysis and Design in a Changing World, 6th Edition 30
Data Flow Definitions RMO products and items report defined using algebraic
notation. Note nested repeating groups like typical control break report.
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Systems Analysis and Design in a Changing World, 6th Edition 31
Data Dictionary and Other Definitions Data dictionary – a repository for definitions of data
flows, data elements, and data stores A data store on the DFD represents a data entity on
the ERD, no separate definition is typically needed Data element definitions
Describe a data type, such as string, integer, floating point, or Boolean
Each element should also be defined to indicate specifically what it represents and how it is validated
Use the person from Mars concept—would someone from Mars know what element means?
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Systems Analysis and Design in a Changing World, 6th Edition 32
Data Element Definitions
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Systems Analysis and Design in a Changing World, 6th Edition 33
Locations and Communication Through Networks
Location diagram – a diagram or map that identifies all the processing locations of a system
Activity-location matrix – a table that describes the relationship between processes and the locations in which they are performed
Activity-data matrix – a table that describes stored data entities, the locations from which they are accessed, and the nature of the accesses
CRUD – acronym for create, read, update, and delete
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Systems Analysis and Design in a Changing World, 6th Edition 34
RMO Location Diagram
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Systems Analysis and Design in a Changing World, 6th Edition 35
RMO Activity-Location Matrix
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Systems Analysis and Design in a Changing World, 6th Edition 36
RMO Activity-Data Matrix
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Systems Analysis and Design in a Changing World, 6th Edition 37
Summary Data flow diagrams (DFDs) are used in
combination with the use cases and entity-relationship diagram (ERD) to model system requirements
DFDs model a system as a set of processes, data flows, external agents, and data stores
Many types of DFDs are developed, including context diagrams, DFD fragments, subsystem DFDs, diagram 0, and process decomposition DFDs
Each process, data flow, and data store requires a detailed definition
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Systems Analysis and Design in a Changing World, 6th Edition 38
Summary (continued)
Analysts may define processes in a number of ways, including a structured English process specification, a decision table, a decision tree, or a process decomposition DFD
Data flows are defined in terms of their component data elements and their internal structure.
Data elements may be further defined in terms of their type and allowable content
Data stores correspond to entities on the ERD and thus require no additional definition
The location diagram, activity-location matrix, and activity-data matrix describe important information about system locations