2. Chapter 5: Analysis Part I: Object Modeling Part II: Dynamic Modeling Qutaibah Malluhi Software Engineering Qatar University Based on slides by Bernd Bruegge & Allen H. Dutoit

3. Introduction

4. Summary of Previous Discussion Pure functional decomposition is bad:  Leads to unmaintainable code Pure object identification is bad:  May lead to wrong objects, wrong attributes, wrong methods

5. Ambiguity: what do you see?

6. General Approach for Identifying Objects The key to successful analysis:  Start with use cases and then find the participating objects  If somebody asks “What is this?”, do not answer right away. Return the question or observe the end user: “What is it used for?”  Identify system boundary What object is inside, what object is outside?

7. From Use Cases to Objects Level 1 Use Case Level 2 Use Cases Level 3 Use Cases Operations Participating Objects Level 2 Level 1 Level 2 Level 3 Level 3 Level 4 Level 4 Level 3 AB

8. Why Functional Decomposition is not Enough Scenarios Level 1 Use Cases Level 2 Use Cases Operations Participating Objects Level 2 Level 1 Level 2 Level 3 Level 3 Level 4 Level 4 Level 3 AB

9. Analysis Overview

10. Introduction Requirements Design Implementation Testing Analysis System Arch. Design Detailed Design

11. Object Oriented Analysis (Modeling) Requirement elicitation leads to requirements specifications  Functional model (use-case and scenarios)  Non-functional requirements and constraints Analysis focuses on producing a model of the system – analysis model Analysis model is composed of 2 individual models  analysis object model (class and object diagram)  dynamic model (statechart, sequence diagrams)

12. Analysis Phase Inputs - requirements specifications (use cases) Outputs the components of the Analysis Model  dynamic model Develop preliminary sequence diagrams to illustrate the interaction between objects Develop state diagrams for objects with interesting behavior  static model Analysis object model Develop preliminary object and class diagrams showing the structure of the system Heuristics to help create the Analysis Model

13. Requirements Model, Analysis Model, Design Models 1. Analyze the problem statement  Identify functional requirements  Identify nonfunctional requirements  Identify constraints (pseudo requirements) 2. Build the functional model  Develop use cases to illustrate functionality requirements 3. Build the dynamic model  Develop sequence diagrams to illustrate the interaction between objects  Develop state diagrams for objects with interesting behavior 4. Build the static model  Develop object and class diagrams showing the structure of the system 5. Use the analysis model (static and dynamic) to create  system (architecture) design model, and  detailed object design model

14. Figure 5-2, Products of requirements elicitation and analysis. Analysis functional model nonfunctional requirements analysis object model Requirements elicitation dynamic model Requirements Analysis Model Specification System design Object design

15. Object Modeling

16. Outline Activities during object modeling Object identification Object types  entity, boundary and control objects Object naming Abbott’s technique helps in object identification Users of class diagrams

17. Activities during Object Modeling Main goal: Find the important abstractions What happens if we find the wrong abstractions?  Iterate and correct the model Steps during object modeling 1. Class identification Based on the fundamental assumption that we can find abstractions 2. Find the attributes 3. Find the methods 4. Find the associations between classes Order of steps  Goal: get the desired abstractions  Order of steps secondary, only a heuristic  Iteration is important

18. Class Identification Identify the boundaries of the system Identify the important entities in the system Class identification is crucial to object-oriented modeling Should be able to: 1. Find the classes for a new software system (Forward Engineering) 2. Identify the classes in an existing system (Reverse Engineering)

19. Pieces of an Object Model Classes Associations (Relations)  Generic associations  Canonical associations Part of- Hierarchy (Aggregation) Kind of-Hierarchy (Generalization) Attributes  Application specific  Attributes in one system can be classes in another system Operations  Generic operations: Get/Set, General world knowledge, design patterns  Domain operations: Dynamic model, Functional model

20. Object vs. Class Object (instance): Exactly one thing  This lecture on Software Engineering on November 15 from 14:30 - 16:00 A class describes a group of objects with similar properties  Game, Tournament, mechanic, car, database Object diagram: A graphic notation for modeling objects, classes and their relationships ("associations"):  Class diagram: Template for describing many instances of data. Useful for taxonomies, patters, schemata...  Instance diagram: A particular set of objects relating to each other. Useful for discussing scenarios, test cases and examples

21. Class identification Finding objects is the central piece in object modeling Approaches  Application domain approach Ask application domain expert to identify relevant abstractions  Syntactic approach (this set of slides) Start with use cases. Extract participating objects from flow of events Use noun-verb analysis (Abbot’s technique) to identify components of the object model  Design patterns approach (will discuss in later chapters) Use reusable design patterns  Component-based approach (will discuss later chapters) Identify existing solution classes

22. Finding Classes from Use Cases The analysis activities are guided by heuristics  Quality of output very much depends on experience Heuristics for identifying objects  Find terms that developers or users need to clarify in order to understand the flow of events  Look for recurring nouns (e.g., Incident),  Identify real world entities that the system needs to keep track of (e.g., FieldOfficer, Dispatcher, Resource),  Identify real world procedures that the system needs to keep track of (e.g., EmergencyOperationsPlan),  Identify data sources or sinks (e.g., Printer) Be prepared that some objects are still missing and need to be found:  Refine when you model flow of events with a sequence diagram Always use the user’s terms

23. Object Types Entity Objects  Represent the persistent information tracked by the system (Application domain objects, “Business objects”) Boundary Objects  Represent the interaction between the user and the system Control Objects:  Represent the control tasks performed by the system  In charge of realizing use cases Having three types of objects leads to models that are more resilient to change.  The interface of a system changes more likely than the control  The control of the system change more likely than the application domain Concept is similar to Model, View, Controller design pattern  Model, View, Controller (MVC)

24. Example: 2BWatch Objects Year Month Day ChangeDate Button LCDDisplay Entity Objects Control ObjectsInterface Objects

25. Naming of Object Types in UML UML provides several mechanisms to extend the language UML provides the stereotype mechanism to present new modeling elements Stereotypes can be used to distinguish different object types > Year > Month > Day > ChangeDate > Button > LCDDisplay Entity Objects Control ObjectsBoundary Objects

26. Naming Conventions to Distinguish Object Types Can distinguish the different object types on a syntactical basis. E.g., can use suffixes:  Objects ending with the “_Boundary” suffix are boundary objects  Objects ending with the “_Control” suffix are control objects  Entity objects do not have any suffix appended to their name Year Month Day ChangeDate_ Control Button_Boundary LCDDisplay_Boundary

27. Example: Flow of events The customer enters a store with the intention of buying a toy for his child with the age of n. Help must be available within less than one minute. The store owner gives advice to the customer. The advice depends on the age range of the child and the attributes of the toy. The customer selects a dangerous toy which is kind of unsuitable for the child. The store owner recommends a more yellow doll.

28. Mapping parts of speech to object model components [Abbott, 1983] Part of speechModel componentExample Proper nounobjectJim Smith Improper nounclassToy, doll Doing verbmethodBuy, recommend Being verbinheritanceis-a (kind-of) Having verbaggregationhas an Modal verbconstraintmust be Adjectiveattribute3 years old Transitive verbmethodenter Intransitive verbmethod (event)depends on

29. Abbot’s Analysis Example The customer enters the store to buy a toy. It has to be a toy that his daughter likes and it must cost less than $50. He tries a videogame, which uses a data glove and a head-mounted display. He likes it. An assistant helps him. The suitability of the game depends on the age of the child. His daughter is only 3 years old. The assistant recommends another type of toy, namely the board game " Monopoly ". Flow of events: Is this a good use Case? “Monopoly” is probably a left over from the scenario 3 years old also indicates Scenario rather than use case The use case should terminate with the customer leaving the store Not quite!

30. Grammatical constructUML Component Concrete Person, ThingObject Nounclass VerbOperation Classifying verbInheritance Having VerbAggregation Modal VerbConstraint AdjectiveAttribute Intransitive verbOperation (Event) Textual Analysis using Abbot‘s technique Example “Monopoly" “toy" “enters" “is a",“either.. or", “kind of…" "Has a ", “consists of" “must be", “less than…" "3 years old" “depends on…."

31. The customer enters the store to buy a toy. It has to be a toy that his daughter likes and it must cost less than $50. He tries a videogame, which uses a data glove and a head-mounted display. He likes it. Class diagram from flow of events An assistant helps him. The suitability of the game depends on the age of the child. His daughter is only 3 years old. The assistant recommends another type of toy, namely a board game. The customer buy the game and leaves the store type of toy customer depends storeenters Customer ? enter() toydaughter suitable * less than $50 store enter() daughter age toy buy() videogameboardgame toy age videogame daughter board game Flow of events: toy price buy() like() buy likes

32. Example: Identify Classes Title: Search for Supplier Information Preconditions: Dental Office System has been initialized Post-conditions: If the search is successful, then the supplier information is displayed. If the search is not successful, then an error message is displayed. Normal Flow: The Operator requests to search for supplier. The Operator may perform a keyword search using the Boolean operators “not”, “and”, and “or”. The Operator may enter up to three keywords The system displays the name, phone number, fax number, and address of the suppliers that match the search criteria. Alternate Flow The Operator requests to search for supplier. The Operator may perform a keyword search using the Boolean operators “not”, “and”, and “or”. If no matches are found, then the system displays an error message to the Operator.

33. Example: Identify Classes Title: Search for Supplier Information Preconditions: Dental Office System has been initialized Post-conditions: If the search is successful, then the supplier information is displayed. If the search is not successful, then an error message is displayed. Normal Flow: The Operator requests to search for supplier. The Operator may perform a keyword search using the boolean operators “not”, “and”, and “or”. The Operator may enter up to three keywords. The system displays the name, phone number, fax number, and address of the suppliers that match the search criteria to the Operator. Alternate Flow The Operator requests to search for supplier. The Operator may perform a keyword search using the boolean operators “not”, “and”, and “or”. If no matches are found, then the system displays an error message to the Operator.

34. Order of activities in modeling Formulate a few scenarios with help from the end user and/or application domain expert. Extract the use cases from the scenarios, with the help of application domain expert. Analyze the flow of events, for example with Abbot's textual analysis. Generate the class diagrams, which includes the following steps:  Class identification (textual analysis, domain experts).  Identification of attributes and operations (sometimes before the classes are found!)  Identification of associations between classes  Identification of multiplicities  Identification of roles (label associations)

35. Object Modeling in Practice: Class Identification Foo RoutingNo CustomerId Deposit() Withdraw() GetBalance() Class Identification: Name of Class, Attributes and Methods

36. Object Modeling in Practice: Encourage Brainstorming Foo Balance CustomerId Deposit() Withdraw() GetBalance() Account Balance CustomerId Deposit() Withdraw() GetBalance() Naming is important! Is Foo the right name? “Dada” Balance CustomerId Deposit() Withdraw() GetBalance()

37. Object Modeling in Practice ctd Account Balance Deposit() Withdraw() GetBalance() Customer Name CustomerId 1) Find New Objects CustomerId AccountId 2) Iterate on Names, Attributes and Methods Bank Name

38. Object Modeling in Practice: A Banking System Account Betrag Deposit() Withdraw() GetBalance() Customer Name CustomerId AccountI d Bank Name 1) Find New Objects 2) Iterate on Names, Attributes and Methods 3) Find Associations between Objects Has 4) Label the associations 5) Determine the multiplicity of the associations *

39. Practice Object Modeling: Iterate, Categorize! Customer Name CustomerId() Account Balance Deposit() Withdraw() GetBalance() CustomerId AccountI d Bank Name Has * * Savings Account Withdraw() Checking Account Withdraw() Mortgage Account Withdraw()

40. Improving Readability of Class Diagrams Naming  Representative names  Naming conventions Don’t put too many classes into the same package or page  7+-2 (or even 5+-2) Put Taxonomies (inheritance relationships) on a separate diagram

41. Summary System modeling  Object model  Dynamic model  Functional model Object modeling is the central activity  Class identification is a major activity of object modeling  There are some easy syntactic rules to find classes/objects

42. Dynamic Modeling

43. Outline of the Lecture Dynamic modeling  Sequence diagrams  State diagrams Analysis example

44. Dynamic Modeling Diagrams Diagrams for dynamic modeling  Interaction diagrams describe the dynamic behavior between objects  Statecharts describe the dynamic behavior of a single object Interaction diagrams  Sequence Diagram: Dynamic behavior of a set of objects arranged in time sequence. Models the system from a single use case point of view Good for real-time specifications and complex scenarios Statechart Diagram:  A state machine that describes the response of an object of a given class to the receipt of outside stimuli (Events).

45. How do you find classes? We have already established the following sources  Application domain analysis: Talk to client to identify abstractions  Application of general world knowledge and intuition  Scenarios Natural language formulation of a concrete usage of the system  Use Cases Natural language formulation of the functions of the system  Textual analysis of problem statement (Abbott) Now we show how identify classes from dynamic models  Actions and activities in statechart diagrams are candidates for public operations in classes  Vertical activity lines in sequence diagrams are also candidates for objects

46. Find Methods with Dynamic Modeling Purpose:  Detect and supply methods for the object model How do we do this?  Start with use case or scenario  Model interaction between objects sequence diagram  Model dynamic behavior of a single object statechart diagram

47. Sequence Diagram From the flow of events in the use case or scenario proceed to the sequence diagram Relation to object identification:  Objects/classes have already been identified during object modeling  Objects are identified as a result of dynamic modeling Heuristic:  A event (message) always has a sender and a receiver.  Find them for each event => These are the objects participating in the use case

48. Sequence Diagram for ReportEmergency Use Case

50. Sequence diagram for the ReportEmergency use case (acknowledgment on the FieldOfficerStation ).

51. Heuristics for Sequence Diagrams Layout:  1st column: Should correspond to the actor who initiated the use case  2nd column: Should be a boundary object  3rd column: Should be the control object that manages the rest of the use case Creation:  Control objects are created by (input) boundary objects at the initiation of a use case  Boundary objects (for output) are created by control objects Access:  Entity objects are accessed by control and boundary objects,  Entity objects should never call boundary or control objects: This makes it easier to share entity objects across use cases and makes entity objects resilient against technology-induced changes in boundary objects.

52. Sequence Diagram Impact on Object Model Help identify new classes The Sequence Diagram also supplies us with a lot of (new) events/messages  For each object that receives an event there is a public operation in the associated class The name of the operation is usually the name of the event. Help distribute behavior on objects

53. What else can we get out of sequence diagrams? Sequence diagrams are derived from use cases  See/inspect the internal structure of the use cases. Determine how decentralized the system is.  We distinguish two structures for sequence diagrams: Fork diagrams Stair diagrams

54. Fork Diagram Much of the dynamic behavior is placed in a single object, usually the control object. It knows all the other objects and often uses them for direct questions and commands.

55. Stair Diagram The dynamic behavior is distributed. Each object delegates some responsibility to other objects. Each object knows only a few of the other objects and knows which objects can help with a specific behavior.

56. Fork or Stair? Which of these diagram types should be chosen? Generally, stair structure is better  The more the responsibility is spread out, the better However, this is not always true:  Decentralized control structure The operations have a strong connection always be performed in the same order  Centralized control structure (better support of change) The operations can change order New operations can be inserted as a result of new requirements

57. Statechart Diagrams Graph whose nodes are states and whose directed arcs are transitions labeled by event names. We distinguish between two types of operations in statecharts:  Activity: Operation that takes time to complete associated with states  Action: Instantaneous operation associated with events associated with states (reduces drawing complexity): Entry, Exit, Internal Action A statechart diagram relates events and states for one class  An object model with a set of objects has a set of state diagrams

58. UML Statechart Diagram Notation State2 State1 Event1(attr) [condition]/action entry /action exit/action do/Activity Also: internal actions Event trigger With parameters Guard condition

59. Vending Machine StateChart Diagram do: test item and compute change do: make change do: dispense item Idle [item empty] [select(item)] [change=0] [change>0] [change<0] Collect Money coins_in(amount) / add to balance coins_in(amount) / set balance cancel / refund coins

60. Nested State Diagram Activities in states are composite items denoting other lower-level state diagrams A lower-level state diagram corresponds to a sequence of lower-level states and events that are invisible in the higher-level diagram. Sets of substates in a nested state diagram denote a superstate are enclosed by a large rounded box.

61. Nested Statechart for Incident. Active InactiveClosedArchived all whendate > 1yr. resources submitted reports ReportedAssessment DisengagementResponse field officer arrives on site field officer releases resources dispatcher allocates resources field officer requests additional resources all resources deallocated

62. State Chart Diagram vs Sequence Diagram State chart diagrams help to identify:  Changes to an individual object over time Sequence diagrams help to identify  The temporal relationship of between objects over time  Sequence of operations as a response to one ore more events

63. 1. What are the transformations? Create scenarios and use case diagrams Talk to client, observe, get historical records, do thought experiments 2. What is the structure of the system? Create class diagrams Identify objects. What are the associations between them? What is their multiplicity? What are the attributes of the objects? What operations are defined on the objects? 3. What is its behavior? Create sequence diagrams Identify senders and receivers Show sequence of events exchanged between objects. Identify event dependencies and event concurrency. Create state diagrams Only for the dynamically interesting objects. Summary: Requirements Analysis Dynamic Modeling Functional Modeling Object Modeling

64. Let’s Do Analysis 1. Analyze the problem statement  Identify functional requirements  Identify nonfunctional requirements  Identify constraints (pseudo requirements) 2. Build the functional model:  Develop use cases to illustrate functionality requirements 3. Build the dynamic model:  Develop sequence diagrams to illustrate the interaction between objects  Develop state diagrams for objects with interesting behavior 4. Build the object model:  Develop class diagrams showing the structure of the system

65. Problem Statement: Direction Control for a Toy Car Power is turned on  Car moves forward and car headlight shines Power is turned off  Car stops and headlight goes out. Power is turned on  Headlight shines Power is turned off  Headlight goes out. Power is turned on  Car runs backward with its headlight shining. Power is turned on  Car moves forward and car headlight shines Power is turned off  Car stops and headlight goes out. Power is turned on  Headlight shines Power is turned off  Headlight goes out. Power is turned on  Car runs backward with its headlight shining. Power is turned off  Car stops and headlight goes out. Power is turned on  Headlight shines Power is turned off  Headlight goes out. Power is turned on  Car runs forward with its headlight shining. Power is turned off  Car stops and headlight goes out. Power is turned on  Headlight shines Power is turned off  Headlight goes out. Power is turned on  Car runs forward with its headlight shining.

66. Find the Functional Model: Do Use Case Modeling Use case 1: System Initialization  Entry condition: Power is off, car is not moving  Flow of events: Driver turns power on  Exit condition: Car moves forward, headlight is on Use case 2: Turn headlight off  Entry condition: Car moves forward with headlights on  Flow of events: Driver turns power off, car stops and headlight goes out. Driver turns power on, headlight shines and car does not move. Driver turns power off, headlight goes out  Exit condition: Car does not move, headlight is out

67. Use Cases continued Use case 3: Move car backward  Entry condition: Car is stationary, headlights off  Flow of events: Driver turns power on  Exit condition: Car moves backward, headlight on Use case 4: Stop backward moving car  Entry condition: Car moves backward, headlights on  Flow of events: Driver turns power off, car stops, headlight goes out. Power is turned on, headlight shines and car does not move. Power is turned off, headlight goes out.  Exit condition: Car does not move, headlight is out. Use case 5: Move car forward  Entry condition: Car does not move, headlight is out  Flow of events Driver turns power on  Exit condition: Car runs forward with its headlight shining.

68. Use Case Pruning Do we need use case 5? Use case 1: System Initialization  Entry condition: Power is off, car is not moving  Flow of events: Driver turns power on  Exit condition: Car moves forward, headlight is on Use case 5: Move car forward  Entry condition: Car does not move, headlight is out  Flow of events Driver turns power on  Exit condition: Car runs forward with its headlight shining.

69. Find the Dynamic Model: Create sequence diagram Name: Drive Car Sequence of events:  Billy turns power on  Headlight goes on  Wheels starts moving forward  Wheels keeps moving forward  Billy turns power off  Headlight goes off  Wheels stops moving ...

70. Sequence Diagram for Drive Car Scenario :HeadlightBilly:Driver:Wheel Power(on) Power(off) Power(on)

71. Toy Car: Dynamic Model Wheel Forward Backward Stationary power on power off power off power on Headlight power on power off Off On

72. Toy Car: Object Model Wheel Motion: (Forward, Stationary) Backward, Start_Moving() Stop_Moving() Headlight Status: (On, Off) Switch_On() Switch_Off() Power Status: (On, Off) TurnOn() TurnOff() Car

73. Analysis: UML Activity Diagram Generalization relationships, suppress redundancies correct, consistent complete, and realistic?