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  1. Chapter 6-7Analysis ModelingAdapted by Dan Fleck from:- Roger Pressman’s Slides- http://www.informatics.sussex.ac.uk/users/lb203/se/SE04.pdf- Jochen Rick’s slides from GA Institute of Technology- http://webfuse.cqu.edu.au/Courses/aut2001/95169/ Extra_Examples/DFD_Example_1/- System Analysis and Design slides edited by Yale Braunstein Coming up: Requirements Analysis

  2. Earlier • Talked about requirements • Frequently in written form • Supplemented by other analyses

  3. Requirements Analysis • Results in models: • Scenario-based models (from POV of actors) • Data models (information domain for the problem) • Class-oriented models • Flow-oriented models • Behavioral models (how the software behaves according to external events)

  4. Analysis Phase: What is it? Software, hardware, data, human elements Software application architecture, user interface, component-level structure • Three objectives of requirements: • To describe what the customer requires • To establish a basis for the creation of a software design • To define a set of requirements that can be validated once the software is built Coming up: Elements of the Analysis Model

  5. Elements of the Analysis Model Scenario-based elements Flow-oriented elements Use-case diagrams Use cases - text Activity Diagrams Swim lane diagrams Data-flow diagrams Control flow diagrams Processing narratives Analysis Model Class-based elements Behavioral elements Class diagrams Analysis Packages CRC Models Collaboration Diagrams State diagrams Sequence diagrams ER Diagrams Coming up: Elements of the Analysis Model

  6. Typical Classes (a reminder) • External entities - printer, user, sensor • Things - reports, displays, signals • Occurrences or events (e.g., interrupt, alarm) • Roles(e.g., manager, engineer, salesperson) • Organizational units (e.g., division, team) • Places(e.g., manufacturing floor or loading dock) • Structures (e.g., sensors, four-wheeled vehicles, or computers) But, how do we select classes? Coming up: Selecting Classes—Criteria

  7. Selecting Classes—Criteria retained information – information about it must be remembered needed services – operations that change the attributes multiple attributes – if it is only one attribute, probably should be part of another class common attributes – common things for all instances of a class common operations – for all instances of the class essential requirements – appear in the PROBLEM space (remember we’re doing analysis modeling!) Coming up: Selecting Classes—Example

  8. Selecting Classes—Example ATMUser Yes Yes Yes Yes Yes Yes PinNum Yes No No Yes Maybe Yes retained information needed services multiple attributes common attributes common operations essential requirements Coming up: CRC Cards

  9. CRC Cards • Is there a better way to find classes? • Sure… Class Responsibility Collaborator Cards (see CRC slides and book pg 173) Coming up: Elements of the Analysis Model

  10. Elements of the Analysis Model Scenario-based elements Flow-oriented elements Use-case diagrams Use cases - text Activity Diagrams Swim lane diagrams Data-flow diagrams Control flow diagrams Processing narratives Analysis Model Class-based elements Behavioral elements Class diagrams Analysis Packages CRC Models Collaboration Diagrams State diagrams Sequence diagrams ER Diagrams Coming up: The ERD: An Example

  11. The ERD: An Example places request for service Customer standard task table work order generates (1,1) work tasks selected from consists of lists materials Coming up: Data Modeling

  12. Data Modeling • examines data objects independently of processing • focuses attention on the data domain • creates a model at the customer’s level of abstraction • indicates how data objects relate to one another Coming up: What is a Data Object?

  13. What is a Data Object? Object —something that is described by a set of attributes (data items) and that will be manipulated within the software (system) each instance of an object (e.g., a book) can be identified uniquely (e.g., ISBN #) each plays a necessary role in the system i.e., the system could not function without access to instances of the object each is described by attributes that are themselves data items What are some typical data objects? Coming up: Typical Data Objects

  14. Data Objects and Attributes A data object contains a set of attributes that act as an aspect, quality, characteristic, or descriptor of the object object: automobile attributes: make model body type price options code How do data objects differ from OO classes or do they? Coming up: What is a Relationship?

  15. What is a Relationship? • several instances of a relationship can exist • objects can be related in many different ways relationship —indicates “connectedness”; a "fact" that must be "remembered" by the system and cannot or is not computed or derived mechanically Coming up: Crow’s Foot Style ERD

  16. Crow’s Foot Style ERD The ERD: Other style’s exist. There are a few, but most are more confusing and less common than Crow’s foot. Depending on who you ask this was invented by Dr. Gordon Everest or Clive Finkelstein. Teacher teaches 0 to many classes Classes have 1 and only 1 teacher Students have 1 to many addresses An address is for zero to one student (addresses may not be associated with multiple students) Teacher Class Address Student First “thing” denotes optional or mandatory. Second “thing” denotes cardinality (one or many) Coming up: ERD Example: From http://www.b2ttraining.com

  17. ERD Example: From http://www.b2ttraining.com Coming up: Elements of the Analysis Model

  18. Elements of the Analysis Model Onward to data flow diagrams! Scenario-based elements Flow-oriented elements Use-case diagrams Use cases - text Activity Diagrams Swim lane diagrams Data-flow diagrams Control flow diagrams Processing narratives Analysis Model Class-based elements Behavioral elements Class diagrams Analysis Packages CRC Models Collaboration Diagrams State diagrams Sequence diagrams Coming up: Flow-Oriented Modeling

  19. Flow-Oriented Modeling • Represents how data objects are transformed at they move through the system • A data flow diagram (DFD) is the diagrammatic form that is used to show how data is transformed as it moves through the system • Considered by many to be an ‘old school’ approach, flow-oriented modeling continues to provide a view of the system that is unique—it should be used to supplement other analysis model elements Coming up: The Flow Model

  20. The Flow Model Every computer-based system is an information transform .... computer based system data input output Coming up: Flow Modeling Notation

  21. Flow Modeling Notation external entity process data flow data store Coming up: External Entity

  22. External Entity A producer or consumer of data Examples: a person, a device, a sensor Data must always originate somewhere and must always be sent to something Coming up: Process

  23. Process A data transformer (changes input to output) Examples: compute taxes, determine area, format report, display graph Data must always be processed in some way to achieve system function Coming up: Data Flow

  24. Data Flow Data flows through a system, beginning as input and be transformed into output. base compute triangle area area height Key thought: In a DFD the DATA is what is moving on the arrows! Coming up: Data Stores

  25. Data Stores Datais often stored for later use. sensor # sensor #, type, location, age look-up sensor data report required type, location, age sensor number sensor data In a real system what things are “Data Stores”? Coming up: Data Flow Diagramming:Guidelines

  26. Data Flow Diagramming:Guidelines • all icons must be labeled with meaningful names • the DFD evolves through a number of levels of detail • always begin with a context level diagram (also called level 0) • always show external entities at level 0 • always label data flow arrows • do not represent procedural logic • ensure that you show DATA moving through the system (not control) Coming up: Constructing a DFD—I

  27. Constructing a DFD—I • review the data model to isolate data objects and use a grammatical parse to determine “operations” • determine external entities (producers and consumers of data) • create a level 0 DFD Coming up: Level 0 DFD Examples

  28. Level 0 DFD Examples processing request user requested video signal digital video processor monitor video source NTSC video signal Coming up: Constructing a DFD—II

  29. Constructing a DFD—II • write a narrative describing the transform • parse to determine next level transforms • “balance” the flow to maintain data flow continuity • develop a level 1 DFD • use a 1:5 (approx.) expansion ratio Coming up: The Data Flow Hierarchy

  30. The Data Flow Hierarchy a b P x y level 0 c p2 a f p1 b p4 d 5 g p3 e level 1 Coming up: Example DFD: Level 1

  31. Example DFD: Level 1 Coming up: DFD: A practical example

  32. DFD: A practical example Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin. Coming up: DFD Example

  33. DFD Example • Example from http://ldtconsultinginc.com/ • Can we add labels to unlabled data flows? • Is this a level 0 diagram? Coming up: Lets Try It

  34. Lets Try It • Lets create a DFD for • A carpet cleaning business • A web-based order processing system for a computer store • An address book for an iPhone Coming up: Flow Modeling Notes

  35. Flow Modeling Notes • each bubble is refined until it does just one thing • the expansion ratio decreases as the number of levels increase • most systems require between 3 and 7 levels for an adequate flow model • a single data flow item (arrow) may be expanded as levels increase (data dictionary provides information) • The things that move on the arrows are DATA! Coming up: Elements of the Analysis Model

  36. Elements of the Analysis Model Scenario-based elements Flow-oriented elements Use-case diagrams Use cases - text Activity Diagrams Swim lane diagrams Data-flow diagrams Control flow diagrams Processing narratives Analysis Model Oh behave! Class-based elements Behavioral elements Class diagrams Analysis Packages CRC Models Collaboration Diagrams State diagrams Sequence diagrams Coming up: Behavioral Modeling

  37. Behavioral Modeling • The behavioral model indicates how software will respond to external events or stimuli. To create the model, the analyst must perform the following steps: • Evaluate all use-cases to fully understand the sequence of interaction within the system. • Identify events that drive the interaction sequence and understand how these events relate to specific objects. • Create a sequence diagram for each use-case. • Build a state diagram for the system. • Review the behavioral model to verify accuracy and consistency. Coming up: State Representations

  38. State Representations • In the context of behavioral modeling, two different characterizations of states must be considered: • the state of each class as the system performs its function and • the state of the system as observed from the outside as the system performs its function • What are some states for an ATM machine? Washing machine? Cell phone? Coming up: State Diagram for the ControlPanel Class

  39. State Diagram for the ControlPanel Class Coming up: State Diagram Details

  40. State Diagram Details State Name (verb in current tense) (Optional) actions happening during state [age <= 20] [age > 20] [age <= 20]/setFlag(false) Guards: Use to describe event that causes a state transition happens (ALL transitions should have guards) Name Examples: sorting validating updating status … Action: If something happens while transitioning to another state. (Optional) Coming up: The States of a System

  41. The States of a System • state—a set of observable circumstances that characterizes the behavior of a system at a given time • state transition—the movement from one state to another • event—an occurrence that causes the system to exhibit some predictable form of behavior • action—process that occurs as a consequence of making a transition Coming up: Behavioral Modeling

  42. Behavioral Modeling • make a list of the different states of a system (How does the system behave?) • indicate how the system makes a transition from one state to another (How does the system change state?) • indicate event • indicate action • draw a state diagram or a sequence diagram Coming up: State Diagram - Lets Try It!

  43. State Diagram - Lets Try It! You are designing a traffic light system for this intersection. Draw a state diagram showing the different states and how they transition. North West East South Coming up: Elements of the Analysis Model

  44. Elements of the Analysis Model Scenario-based elements Flow-oriented elements Use-case diagrams Use cases - text Activity Diagrams Swim lane diagrams Data-flow diagrams Control flow diagrams Processing narratives Analysis Model Class-based elements Behavioral elements Class diagrams Analysis Packages CRC Models Collaboration Diagrams State diagrams Sequence diagrams Coming up: Object Oriented Analysis (OOA)

  45. Object Oriented Analysis (OOA) • The intent of OOA is to define all classes (and the relationships and behavior associated with them) that are relevant to the problem to be solved. For that, a number of tasks must occur: • Classes must be identified (i.e., attributes and methods) • A class hierarchy is defined • Object-to-object relationships should be represented • Object behavior must be modeled • Tasks 1 through 4 are reapplied iteratively Coming up: Object-Oriented Concepts

  46. Analysis Model Rules of Thumb • The model should focus on requirements that are visible within the problem or business domain. The level of abstraction should be relatively high. • Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system. • Delay consideration of infrastructure and other nonfunctional models until design • Minimize coupling throughout the system. • Be certain that the analysis model provides value to all stakeholders. • Keep the model as simple as it can be. Coming up: Analysis Phase: What is it?

  47. Writing the Software Specification Everyone knew exactly what had to be done until someone wrote it down! Read the last three slides on your own Coming up: Specification Guidelines

  48. Specification Guidelines Coming up: Specification Guidelines

  49. Specification Guidelines Coming up: Specification Guidelines

  50. Specification Guidelines End of presentation

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