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Introduction to Software Engineering 
Muhammad Nasir 
Requirements Modeling – Data 
Flow & Behavior 
m.nasir@iiu.edu.pk
Agenda 
 Requirement Modeling Strategies 
 Flow Oriented Modeling 
 Elements of Structured Analysis 
 Data Flow Diagra...
Requirement Modeling Strategies
Requirement Modeling Strategies 
 One view of requirements modeling, called 
structured analysis, considers data and 
the...
Requirement Modeling Strategies 
 A second approach to analysis 
modeled, called object-oriented 
analysis, focuses on th...
Requirement Modeling Strategies 
 Although the analysis model that we discuss 
combines features of both approaches. 
 T...
Flow-Oriented Modeling 
 Although data flow-oriented 
modeling is perceived as an 
outdated technique by some 
software e...
Flow-Oriented Modeling 
 Although the data flow diagram 
(DFD) and related diagrams and 
information are not a formal par...
Elements of Structured Flow 
Oriented Analysis 
 Entity Relationship Diagram (ERD) 
 Data Flow Diagram (DFD)
Data Flow Diagram - DFD 
 The DFD takes an input-process-output 
view of a system. 
 That is, data objects flow into the...
Data Flow Diagram - DFD 
 The DFD is presented in a hierarchical 
fashion. 
 That is, the first data flow model 
(someti...
Context-level DFD for the 
SafeHome security System
Guidelines for Creating DFD 
1 - The level 0 data flow diagram should 
depict the software/system as a single 
bubble 
2 -...
Guidelines for Creating DFD 
4 - All arrows and bubbles should be 
labeled with meaningful names 
5 - Information flow con...
Creating Level – 1 : DFD 
 The level 0 DFD must now be expanded 
into a level 1 data flow model. 
 But how do we proceed...
Grammatical Parsing
Creating Level – 1 : DFD 
 Referring to the grammatical parse, verbs 
are SafeHome processes and can be 
represented as b...
Level – 1: DFD for the 
SafeHome security System
Level – 2: DFD for the Monitor 
Sensor Processes
UML Flow Oriented Elements 
 Activity Diagram 
 State Transition Diagram 
 Sequence Diagram
The End 
 Thanks for listening 
 Questions would be appreciated.
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Lecture 14 requirements modeling - flow and behavior

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Introduction to Software Engineering 1

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Lecture 14 requirements modeling - flow and behavior

  1. 1. Introduction to Software Engineering Muhammad Nasir Requirements Modeling – Data Flow & Behavior m.nasir@iiu.edu.pk
  2. 2. Agenda  Requirement Modeling Strategies  Flow Oriented Modeling  Elements of Structured Analysis  Data Flow Diagram  Guidelines for Creating DFD  Context Level Diagram (0 Level DFD)  Level – 1 DFD  Level – 2 DFD
  3. 3. Requirement Modeling Strategies
  4. 4. Requirement Modeling Strategies  One view of requirements modeling, called structured analysis, considers data and the processes that transform the data as separate entities.  Data objects are modeled in a way that defines their attributes and relationships.  Processes that manipulate data objects are modeled in a manner that shows how they transform data as data objects flow through the system.
  5. 5. Requirement Modeling Strategies  A second approach to analysis modeled, called object-oriented analysis, focuses on the definition of classes and the manner in which they collaborate with one another to effect customer requirements.
  6. 6. Requirement Modeling Strategies  Although the analysis model that we discuss combines features of both approaches.  The question is not which is best, but rather, what combination of representations will provide stakeholders with the best model of software requirements and the most effective bridge to software design.
  7. 7. Flow-Oriented Modeling  Although data flow-oriented modeling is perceived as an outdated technique by some software engineers,  It continues to be one of the most widely used requirements analysis notations in use today.
  8. 8. Flow-Oriented Modeling  Although the data flow diagram (DFD) and related diagrams and information are not a formal part of UML,  They can be used to complement UML diagrams and provide additional insight into system requirements and flow.
  9. 9. Elements of Structured Flow Oriented Analysis  Entity Relationship Diagram (ERD)  Data Flow Diagram (DFD)
  10. 10. Data Flow Diagram - DFD  The DFD takes an input-process-output view of a system.  That is, data objects flow into the software, are transformed by processing elements, and resultant data objects flow out of the software.  Data objects are represented by labeled arrows, and transformations are represented by circles (also called bubbles).
  11. 11. Data Flow Diagram - DFD  The DFD is presented in a hierarchical fashion.  That is, the first data flow model (sometimes called a level 0 DFD or context diagram) represents the system as a whole.  Subsequent data flow diagrams refine the context diagram, providing increasing detail with each subsequent level.
  12. 12. Context-level DFD for the SafeHome security System
  13. 13. Guidelines for Creating DFD 1 - The level 0 data flow diagram should depict the software/system as a single bubble 2 - Primary input and output should be carefully noted 3 - Refinement should begin by isolating candidate processes, data objects, and data stores to be represented at the next level
  14. 14. Guidelines for Creating DFD 4 - All arrows and bubbles should be labeled with meaningful names 5 - Information flow continuity must be maintained from level to level and 6 - One bubble at a time should be refined.
  15. 15. Creating Level – 1 : DFD  The level 0 DFD must now be expanded into a level 1 data flow model.  But how do we proceed?  Apply “grammatical parse”  That is, we isolate all nouns (and noun phrases) and verbs (and verb phrases) in a SafeHome processing narrative derived during the first requirements gathering meeting.
  16. 16. Grammatical Parsing
  17. 17. Creating Level – 1 : DFD  Referring to the grammatical parse, verbs are SafeHome processes and can be represented as bubbles in a subsequent DFD.  Nouns are either external entities (boxes), data or control objects (arrows), or data stores (double lines).  The refinement of DFDs continues until each bubble performs a simple function.
  18. 18. Level – 1: DFD for the SafeHome security System
  19. 19. Level – 2: DFD for the Monitor Sensor Processes
  20. 20. UML Flow Oriented Elements  Activity Diagram  State Transition Diagram  Sequence Diagram
  21. 21. The End  Thanks for listening  Questions would be appreciated.
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Introduction to Software Engineering 1

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