1. Systems Analysis and Design in a Changing World, 6th Edition
Online Chapter B
Systems Analysis and Design in a Changing World, 6th Edition

2. The Traditional Approach to Requirements
Online Chapter B
Systems Analysis and Design in a Changing World 6th Ed
Satzinger, Jackson & Burd

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

4. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition

5. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition

6. Traditional vs. OO Approach
Systems Analysis and Design in a Changing World, 6th Edition

7. Requirements Models for Traditional vs. OO Approach
Systems Analysis and Design in a Changing World, 6th Edition

8. Data Flow Diagram Symbols
Systems Analysis and Design in a Changing World, 6th Edition

9. DFD for process Look up item availability
Systems Analysis and Design in a Changing World, 6th Edition

10. Systems Analysis and Design in a Changing World, 6th Edition
DFD Decomposes To show different levels of abstraction Context Diagram Diagram 0 Diagram 1
Systems Analysis and Design in a Changing World, 6th Edition

11. DFD Fragments One for each use case
Systems Analysis and Design in a Changing World, 6th Edition

12. Combine DFD Fragments To Create Diagram 0
Systems Analysis and Design in a Changing World, 6th Edition

13. RMO Data Flow Diagrams Context Diagram
Systems Analysis and Design in a Changing World, 6th Edition

14. RMO Subsystems and Use Cases
Systems Analysis and Design in a Changing World, 6th Edition

15. Context Diagram for RMO Order Entry Subsystem
Systems Analysis and Design in a Changing World, 6th Edition

16. DFD Fragments for RMO Order Entry Subsystem
Systems Analysis and Design in a Changing World, 6th Edition

17. Diagram 0 for RMO Order Entry Subsystem
Systems Analysis and Design in a Changing World, 6th Edition

18. Decomposing Process 2 from DFD Fragment 2
Systems Analysis and Design in a Changing World, 6th Edition

19. Physical DFDs Sometimes useful for modeling processes
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
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
Systems Analysis and Design in a Changing World, 6th Edition

22. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition

23. Structured English Example
Systems Analysis and Design in a Changing World, 6th Edition

24. RMO Process 2.1 Structured English
Systems Analysis and Design in a Changing World, 6th Edition

25. Structured English to determine delivery charges
Systems Analysis and Design in a Changing World, 6th Edition

26. Decision Table calculating shipping charges
Systems Analysis and Design in a Changing World, 6th Edition

27. Decision Tree calculating shipping charges
Systems Analysis and Design in a Changing World, 6th Edition

28. Decision Table with multiple action rows
Systems Analysis and Design in a Changing World, 6th Edition

29. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition

30. Systems Analysis and Design in a Changing World, 6th Edition
Data Flow Definitions
RMO products and items report defined using algebraic notation. Note nested repeating groups like typical control break report.
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?
Systems Analysis and Design in a Changing World, 6th Edition

32. Data Element Definitions
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
Systems Analysis and Design in a Changing World, 6th Edition

34. Systems Analysis and Design in a Changing World, 6th Edition
RMO Location Diagram
Systems Analysis and Design in a Changing World, 6th Edition

35. RMO Activity-Location Matrix
Systems Analysis and Design in a Changing World, 6th Edition

36. RMO Activity-Data Matrix
Systems Analysis and Design in a Changing World, 6th Edition

37. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition

38. Systems Analysis and Design in a Changing World, 6th Edition
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
Systems Analysis and Design in a Changing World, 6th Edition