1. Chapter 5, Analysis: Dynamic Modeling

2. Reverse Engineering Challenge
Date: Next Tuesday, May 15th
Rules:
We start at exactly at 12:50
10 Minutes introduction to the problem
35 minutes development time for the solution
You have to do the development in the lecture hall
Bring your own laptop (well charged!)
Collaboration is ok: Team work is encouraged
Pair programming (solo and triple also ok)
First Prize:
First person, who finishes a solution that executes and can be demonstrated on lecturer laptop
Second prize:
Lottery among all the solutions submitted by the end of the lecture (by 13:35).
Laptop with usb-port

3. How can you prepare for this event?
Visit the Challenge-Website (see lecture portal)
Prepare your development environment:
Download Eclipse
Download the Bumper system
Compile and run Bumpers
Inspect the source code
Work through the video tutorials.

4. Bumpers-Demo

5. I cannot follow the lectures. Where are we?
We have covered Ch 1 - 4
We are in the middle of Chapter 5
Functional modeling: Read again Ch 2, pp
Structural modeling: Read again Ch 2, pp
From use cases to class diagrams
Identify participatory objects in flow of events descriptions
Exercise: Apply Abbot’s technique to Fig. 5-7, p. 181
Identify entity, control and boundary objects
Heuristics to find these types: Ch 5, Section 5.4
We are now moving into dynamic modeling
Notations for dynamic models are
Interaction-, Collaboration-, Statechart-, Activity diagrams
Reread Ch. 2, pp
The lectures do not follow the book verbatim
The best way to prepare for the lecture is to read the relevant material before the lecture
We are in the middle of Chapter 4
Functional modeling: Scenarios and Use casesReread Ch 2, pp
Structural modeling: Class diagrams: Reread Ch 2, pp

6. Outline of the Lecture Dynamic modeling
Interaction Diagrams
Sequence diagrams
Collaboration diagrams
State diagrams
Using dynamic modeling for the design of user interfaces
Requirements analysis model validation
Design Patterns
Reuse of design knowledge
A first design pattern: the composite pattern.

7. How do you find classes?
We have already established several sources for class identification:
Application domain analysis: We find classes by talking to the client and identify abstractions by observing the end user
General world knowledge and intuition
Textual analysis of event flow in use cases (Abbot)
Today we identify classes from dynamic models
Two good heuristics:
Actions and activities in state chart diagrams are candidates for public operations in classes
Activity lines in sequence diagrams are candidates for objects.
Goal: Come up with
> a domain model (domain specific objects)
> a taxonomy (class hierarchy)

8. Dynamic Modeling with UML
Two UML diagrams types for dynamic modeling:
Interaction diagrams describe the dynamic behavior between objects
Statechart diagrams describe the dynamic behavior of a single object.
Parts of the DAIMLER system has a rich dynamic behavior, so the dynamic model is important.
Note that the dynamic model is an abstraction like the other models as well. Depending on what properties are most characteristic in a system, one of the models will be richer or more significant than others. If you have a choice to decide on a single model, which one would you use?
Object Model: Database, Preventive maintenance,
Dynamic Model: Communication, Notification Server, AGTS Server, Change management (Information flow!)
Temporal relationships are difficult to understand. Rumbaugh thinks, that a system can be best understood by first examining its static structure, that is the structure of its objects and their relationships to each other at a single moment in time. Then we examine the changes to the objects and their relationships over time. (Note that not everybody thinks that way. Heraklit: Everything flows (requires dynamic modeling first), Jacobsen: Use cases (Functional description)
Control is that aspect of a system that describes the sequences of operations that occur in response to external stimuli, without consideration of what the operations do, what the operate on or how they are implemented.
The major concepts of dynamic modeling are events which represent external stimuli and states, which represent the values of objects.
We will use state diagrams, which are a standard computer science concept. Question: Who does not know what a finite state automaton is?
In general we assume, that FSA are covered in (Algorithms and Datastructures)
Similar to the problem in object modeling, we need to avoid to clutter our state diagrams (spaghetti diagrams). We will show that states and events can be organized into generalization hierarchies that share structure and behavior.

9. UML Interaction Diagrams
Two types of interaction diagrams:
Sequence Diagram:
Describes the dynamic behavior of several objects over time
Good for real-time specifications
Collaboration Diagram:
Shows the temporal relationship among objects
Position of objects is based on the position of the classes in the UML class diagram.
Does not show time,
Sequence Diagram:
Describes the dynamic behavior of a set of objects arranged in time sequence.
Good for real-time specifications and complex scenarios

10. UML State Chart Diagram
A state machine that describes the response of an object of a given class to the receipt of outside stimuli (Events).
Activity Diagram:
A special type of state chart diagram, where all states are action states (Moore Automaton).
Sequence Diagram:
Describes the dynamic behavior of a set of objects arranged in time sequence.
Good for real-time specifications and complex scenarios

11. Dynamic Modeling Definition of a dynamic model:
Describes the components of the system that have interesting dynamic behavior
The dynamic model is described with
State diagrams: One state diagram for each class with interesting dynamic behavior
Classes without interesting dynamic behavior are not modeled with state diagrams
Sequence diagrams: For the interaction between classes
Purpose:
Detect and supply operations for the object model.

12. How do we detect Operations?
We look for objects, who are interacting and extract their “protocol”
We look for objects, who have interesting behavior on their own
Good starting point: Flow of events in a use case description
From the flow of events we proceed to the sequence diagram to find the participating objects.

13. What is an Event? Something that happens at a point in time
An event sends information from one object to another
Events can have associations with each other:
Causally related:
An event happens always before another event
An event happens always after another event
Causally unrelated:
Events that happen concurrently
Events can also be grouped in event classes with a hierarchical structure => Event taxonomy

14. The term ‘Event’ is often used in two ways
Instance of an event class:
“Slide 14 shown on Thursday May 9 at 8:50”.
Event class “Lecture Given”, Subclass “Slide Shown”
Attribute of an event class
Slide Update(7:27 AM, 05/07/2009)
Train_Leaves(4:45pm, Manhattan)
Mouse button down(button#, tablet-location)

15. Sequence Diagram
A sequence diagram is a graphical description of the objects participating in a use case using a DAG notation
Heuristic for finding participating objects:
A event always has a sender and a receiver
Find them for each event => These are the objects participating in the use case.
From the flow of events in the use case or scenario we proceed to the sequence diagram
A sequence diagram is a graphical description of objects participating in a use case or scenario using a DAG (direct acyclic graph) notation
Heuristic for finding participating objects:
A event always has a sender and a receiver.
The representation of the event is sometimes called a message
Find them for each event => These are the objects participating in the use case
Relation to object identification:
Objects/classes have already been identified during object modeling
Objects are identified as a result of dynamic modeling

16. An Example Flow of events in “Get SeatPosition” use case :
1. Establish connection between smart card and onboard computer
2. Establish connection between onboard computer and sensor for seat
3. Get current seat position and store on smart card
Where are the objects?
This is an example of a use case that describes the establishment of connection between a technician onboard
the train trying to talk to a maintenance expert currently located at an unknown location.
The location is known by Headquarters.
The Technician has to first reach headquarters to find the expert and is doing this via communication
to the Wayside (Field Site) computer.

17. Sequence Diagram for “Get SeatPosition”
Smart Card
Onboard Computer
Seat
time
1. Establish connection between smart card and onboard computer
2. Establish connection between onboard computer and seat (actually seat sensor)
3. Get current seat position and store on smart card.
Establish Connection
Establish Connection
The Technician informs the Wayside Computer that he/she would like to setup a connection to the Maintenance Expert (1). The Wayside Computer attempts to resolve the name of the Maintenance Expert in Pittsburgh, but that person cannot be located here (2). Thus, the Wayside Computer issues the setup connection event to the Headquarter Computer to find out where the Maintenance Expert is located (3). The Headquarter Computer is able to resolve the name of the Maintenance Expert since this person is located at AEG Headquarters (4). The setup connection is thus finally forwarded to the appropriate Maintenance Expert (5). The Maintenance Expert can reject or accept the connection. If he/she accepts the connection, then the scenario continues as follows (6). The Headquarter Computer establishes a connection to the Maintenance Expert (7). The Headquarter Computer then accepts a connection from the Way-side Computer to complete the second leg of the of the connection (8). In turn, the Wayside Com-puter establishes a connection to the Headquarter Computer (9). The Wayside Computer now accepts the connection from the Technician (10). Finally, the Technician establishes a connection to the Wayside Computer (11). The communication channel is now established from the Techni-cian to the Maintenance Expert and the two parties can exchange information (12).
Accept Connection
Accept Connection
Get SeatPosition
“500,575,300”

18. Heuristics for Sequence Diagrams
Layout:
1st column: Should be the actor of 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 of objects:
Create control objects at beginning of event flow
The control objects create the boundary objects
Access of objects:
Entity objects can be accessed by control and boundary objects
Entity objects should not access boundary or control objects.
Access of objects
Entity objects are accessed by control and boundary objects
Entity objects should never access 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.

19. ARENA Sequence Diagram: Create Tournament
League
Owner
:Tournament
Boundary
:Arena
:League
newTournament
(league)
:Announce
Tournament
Control
«new»
checkMax
Tournament()
setName(name)
setMaxPlayers
(maxp)
createTournament
(name, maxp)
commit()
create
Tournament
(name, maxp)
:Tournament
«new»

20. Impact on ARENA’s Object Model
Let’s assume ARENA’s object model contains - at this modeling stage - the objects
League Owner, Arena, League, Tournament, Match and Player
The Sequence Diagram identifies 2 new Classes
Tournament Boundary, Announce_Tournament_Control
Let’s assume, before we formulated the sequence diagram on the last slide,
ARENA’s object model contained the objects

21. League
Owner
League 1 *
Attributes
Attributes
Operations
Operations
Tournament
Attributes
Operations
Player
Match * *
Attributes
Attributes
Operations
Operations

22. Announce_ Tournament_ Control
League
Owner
League 1 *
Attributes
Attributes
Operations
Operations
Attributes
Operations
Tournament_
Boundary
Tournament
Attributes
Operations
Announce_
Tournament_
Control
Attributes
Operations
Player
Match * *
Attributes
Attributes
Operations
Operations

23. Impact on ARENA’s Object Model (2)
The sequence diagram also supplies us with many new events
newTournament(league)
setName(name)
setMaxPlayers(max)
commit
checkMaxTournament()
createTournament
The sequence diagram supplied us with many new events
Let’s take a look at the way, an event leads to a new method. Let’s take the event createTournament
Question:
Who owns these events?
Answer:
For each object that receives an event there is a public operation in its associated class
The name of the operation is usually the name of the event.

24. Example from the Sequence Diagram
League
Owner
:Tournament
Boundary
:Arena
:League
newTournament
(league)
:Announce
Tournament
Control
«new»
createTournament is a public operation offered by Announce_Tournament_Control
checkMax
Tournament()
setName(name)
setMaxPlayers
(maxp)
commit()
create
Tournament
(name, maxp)
createTournament
(name, maxp)
:Tournament
«new»

25. This is the corresponding view in the UML class diagram:
League
Owner
League 1 *
Attributes
Attributes
Operations
Operations
Attributes
Operations
Tournament_
Boundary
Tournament
Announce_
Tournament_
Control
This is the corresponding view in the UML class diagram:
createTournament is a public operation offered by Announce_Tournament_Control
Attributes
Operations
Attributes
createTournament
(name, maxp)
Player
Match * *
Attributes
Attributes
Operations
Operations

26. What else can we get out of Sequence Diagrams?
Sequence diagrams are derived from use cases
The structure of the sequence diagram helps us to determine how decentralized the system is
We distinguish two structures for sequence diagrams
Fork Diagrams and Stair Diagrams (Ivar Jacobsen)
In some sense, they allow us see the structure of the use cases

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

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

29. Fork or Stair?
Object-oriented supporters claim that the stair structure is better
Modeling Advice:
Choose the stair - a decentralized control structure - if
The operations have a strong connection
The operations will always be performed in the same order
Choose the fork - a centralized control structure - if
The operations can change order
New operations are expected to be added as a result of new requirements.
Which of these diagram types should be chosen?
Object-oriented supporters claim that the stair structure is better
The more the responsibility is spread out, the better
However, this is not always true.

30. Dynamic Modeling We distinguish between two types of operations:
Activity: Operation that takes time to complete
associated with states
Action: Instantaneous operation
associated with events
A state chart diagram relates events and states for one class
An object model with several classes with interesting behavior has a set of state diagrams
A state diagram relates events and states for one object. It is a Graph whose nodes are states
and whose directed arcs are transitions labeled by event names
A transition is drawn from
State diagrams would be quite useless if they only describe event patterns. A behavioral description of an object must specify what the object does in response to events. This is specified in operations attached to states and transition .
An activity is an operation that takes time to complete. Activities are always associated with a state. The notation do Activity1 within a state box indicates that activity A start on entry to the state and stops when complete.
Sometimes it is more advantageous to associate an action with a state. When? When all the state transitions cause the same action, it is a better notational convenience to list the action only once. This reduces clutter in the state diagrams.
An action is an instantaneous operation. This is of course a relative notion. What we mean by instantaneous is that the duration of the operation is insignificant when compared to the time resolution of the state diagram. It also means we do not care about the internal structure of this operation. An action is therefore associated with an event.

31. UML Statechart Diagram Notation
Action
Name of
State
Event with parameters attr
State1
State2
Event
Event(attr) [condition]/action
do/Activity
Guard
condition
entry /action
exit/action
A state is drawn as a rounded box containing a name. The state name appears in bold face
A transition is drawn as an arrow from the receiving state to the target state. Event names are written on the transition arrow, optionally followed by one or more attributes within parentheses.
A condition is a Bollean function of object values, such as emission is above legal value. Conditions can be guards on transitions. A guarded transition fires only when the event occurs and the condition is true. Conditions are shown as expressions in square brackets following the event name and its parameter list.
An action follows the event name and/or the condition by the slash (/) character.
Events that cause an action without causing a state change are written inside the state box. Internal action and self-transition are different. When an internal action occurs, neither the entry nor exit action is executed, when a self-transition occurs, these actions are executed.
Events sent to other objects are shown in dashed lines.
Actions and Activities in State
Note:
Events are italics
Conditions are enclosed with brackets: []
Actions and activities are prefixed with a slash /
Notation is based on work by Harel
Added are a few object-oriented modifications.

32. Example of a StateChart Diagram
coins_in(amount) / set balance
Collect Money
coins_in(amount) / add to balance
Idle
cancel / refund coins
[item empty]
[select(item)]
[change<0]
A good application for nested state diagrams in this example of a vending machine. Here we see the top level dynamic model of the object vending machine, which certainly has interesting dynamic behavior for the designer.
Question to the students: Is the dynamic model interesting for the end user? If the end user has the choice of one of the 3 models (Object model, dynamic model and functional model), which one would they use? Answer: The functional model! If I select this particular candy bar, then that is what I want to get.
Notice the activity do : dispense item. In the case, when we really have to engineer (develop) the dispenser, there is much more to it than just a activity dispense. Note, by the way, that this particular state does not have a name! The state in the upper left has a state, namely Collect Money. This is incomplete if we insist that all states have names, but it is completely natural while we do dynamic modeling. We do not necessarily immediately come up with good names for everything. We had encountered a similar problem during object modeling: In some cases, we found the class name first, in others we first find the method or methods or maybe we start with something where we only know the attribute.
There is no predefined roadmap to arrive at good models, be it object, dynamic or functional models. Creativity cannot be forced into a Procustres bed, or otherwise we will end up with an empty set of boxes!
do/Test item and compute change
[change=0]
[change>0]
do/Dispense item
do/Make change

33. State An abstraction of the attributes of a class
State is the aggregation of several attributes a class
A state is an equivalence class of all those attribute values and links that do no need to be distinguished
Example: State of a bank
State has duration
An abstraction of the attributes of a class
State is the aggregation of several attributes a class
A state is an equivalence class of all those attribute values and links that do no need to
be distinguished as far as the control structure of the class or the the system is concerned
Example: State of a bank
A bank is either solvent or insolvent
State has duration
An object model describes the possible patterns of objects, attribute values and links that can exist in a system.
A dynamic model describes the possible patterns of states, events and actions that can exist in a system.
Over time, the objects stimulate each other, resulting in a series of changes to their states.
An individual stimulus from one object to another is called an event.
Events can be organized into classes. Events can be error conditions as well as normal occurences. Event as an object : Some events are only signals (OK), others have attributes associated with them (Unix signals: Bus error, Segment violation).
Attributes are shown in parentheses after the class name. Events are important for UI, Communication and Notification. Other groups have to worry about events as well, because the interaction between the subsystems should be via the Request Broker.
The response to an event depends on the state of the object receiving it. It can include a state change or sending of another event to another object and sending a event back to the sender (return result, ok, ...)
The Events and states are duals of one another: An event separates 2 states and a state separates 2 events.

34. 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.

35. Dynamic Modeling of User Interfaces
Statechart diagrams can be used for the design of user interfaces
States: Name of screens
Actions or activities are shown as bullets under the screen name
Statechart diagrams can be used for the design of user interfaces
Also called Navigation Path
States: Name of screens
Graphical layout of the screens associated with the states helps when presenting the dynamic model of a user interface
Activities/actions are shown as bullets under screen name
Often only the exit action is shown
State transitions: Result of exit action
Button click
Menu selection
Cursor movements
Good for web-based user interface design

36. Navigation Path Example
Screen name
Action or
Activity
Diagnostics Menu
User moves cursor to Control Panel or Graph
Control panel
User selects functionality of sensors
Graph
User selects data group and type of graph
Define
User defines a sensor event
from a list of events
State transitions: Result of exit action
Button click
Menu selection
Cursor movements
Good for web-based user interface design
Selection
User selects data group
Field site
Car
Sensor group
Time range
Enable
User can enable a sensor event from a list of sensor events
Disable
User can disable a sensor event from a list of sensor events

37. Practical Tips for Dynamic Modeling
Construct dynamic models only for classes with significant dynamic behavior
Avoid “analysis paralysis”
Consider only relevant attributes
Use abstraction if necessary
Look at the granularity of the application when deciding on actions and activities
Reduce notational clutter
Try to put actions into superstate boxes (look for identical actions on events leading to the same state).
A few practical tips.
The most important one: If you have a couple of hundred objects, that does not necessarily mean that you have a couple of hundred dynamic models.
Only those objects with significant dynamic behavior need to be modeled dynamically.
Also, if two objects have the same dynamic behavior, it is often only necessary to model one of these objects with a dynamic model and then describe with a single sentence that the same dynamic model applies to both objects.
The Power and Headlight classes from our Mini People Mover are a good example. Only one of them needs to be modeled dynamically, because they both have the same identical dynamic behavior.
Because the states are permutations over different values of attribute settings, it is important to use abstraction if necessary to filter out irrelevant attributes. That is, if an attribute is not contributing to the dynamic behavior of an object, it does not have be modeled in the dynamic model. This often helps in reducing the number of states of the state diagram for the object.
What makes up an action and what makes up an activity is relative, as we have already discussed earlier. If in doubt, it is always better to model something first as an action, unless somebody points out that it has internal structure which is relevant for the application, or it has a duration which is significant with respect to the overall lifetime of the object. Example: An alarm “Propulsion System Failure” should be modeled as an activity, because the propulsion system will most probably be down for a while after such a failure.

38. Let’s Do Analysis: A Toy Example
Analyze the problem statement
Identify functional requirements
Identify nonfunctional requirements
Identify constraints (pseudo requirements)
Build the functional model:
Develop use cases to illustrate functional requirements
Build the dynamic model:
Develop sequence diagrams to illustrate the interaction between objects
Develop state diagrams for objects with interesting behavior
Build the object model:
Develop class diagrams for the structure of the system

39. 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.
Headlight shines
Headlight goes out
Car runs backward with its headlight shining
Power is turned off
Car stops and headlight goes out
Power is turned on
Headlight shines
Headlight goes out
Car runs forward with its headlight shining

40. Find the Functional Model: Use Cases
Use case 1: System Initialization
Entry condition: Power is off, car is not moving
Flow of events:
1. 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
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

41. 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
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

42. Use Cases Continued 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

43. Use Case Pruning Do we need use case 5?
Let us compare use case 1 and 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
Exit condition:
Car runs forward with its headlight shining

44. Dynamic Modeling: Create the 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
. . .

45. Sequence Diagram for Drive Car Scenario
:Wheel
:Headlight
Billy:Driver
Power(on)
Power(on)
Power(off)
Power(on)

46. Toy Car: Dynamic Model Wheel Headlight Forward Off power power off on
Stationary
power
off
Off
power
off
power on
Change arrows for Headlight states in opposite directions.
Then ask question: Anybody sees what is wrong with the slide? In many cases the students will identify the arrows pointing in the wrong direction.
Stationary On
Backward
power
off
power on

47. Toy Car: Object Model Car Power Headlight Wheel Train Headlight Wheel
Status: (On, Off)
TurnOn()
TurnOff()
Headlight
Status: (On, Off)
Switch_On()
Switch_Off()
Wheel
Motion: (For
ward,
Stationary)
Backward,
Star
t_Moving()
Stop_Moving()
Let them find the key abstractions: Operator, Train. Then the 3 objects in the train: Power, Headlight, Wheel. Then show that the Power and Headlight objects operate the same way, so only one object is needed to for the event scenario.
Train
Wheel
Motion: (For
ward,
Stationar y)
Backward,
Star
t_Moving()
Stop_Moving()
Power
Headlight
Status: (On, Off)
Status: (On, Of)f
TurnOn()
Switch_On()
TurnOff()
Switch_Of
f()

48. Outline of the Lecture Dynamic modeling
Sequence diagrams
State diagrams
Using dynamic modeling for the design of user interfaces
Analysis example
Requirements analysis model validation

49. Model Validation and Verification
Verification is an equivalence check between the transformation of two models
Validation is the comparison of the model with reality
Validation is a critical step in the development process Requirements should be validated with the client and the user.
Techniques: Formal and informal reviews (Meetings, requirements review)
Requirements validation involves several checks
Correctness, Completeness, Ambiguity, Realistism
Verification is an equivalence check between the transformation of two models:
We have two models, is the transformation between them correct?
Validation:
We don’t have two models, we need to compare one model with reality
“Reality” can also be an artificial system, like an legacy system
Validation is a critical step in the development process Requirements should be validated with the client and the user.
Techniques: Formal and informal reviews (Meetings, requirements review)
Requirements validation involves the following checks
Correctness
Completeness
Ambiguity
Realistism

50. Checklist for a Requirements Review
Is the model correct?
A model is correct if it represents the client’s view of the the system
Is the model complete?
Every scenario is described
Is the model consistent?
The model does not have components that contradict each other
Is the model unambiguous?
The model describes one system, not many
Is the model realistic?
The model can be implemented
Is the model correct?
A model is correct if it represents the client’s view of the the system: Everything in the model represents an aspect of reality
Is the model complete?
Every scenario through the system, including exceptions, is described.
Is the model consistent?
The model does not have components that contradict themselves (for example, deliver contradicting results)
Is the model unambiguous?
The model describes one system (one reality), not many
Is the model realistic?
The model can be implemented without problems

51. Examples for syntactical Problems
Different spellings in different UML diagrams
Omissions in diagrams

52. Different spellings in different UML diagrams
UML Sequence Diagram
UML Class Diagram
Attributes
Operations
League
Tournament
Player
Match
Owner 1 *
Tournament_
Boundary
makeTournament
(name, maxp)
Announce_
Control
createTournament
(name, maxp)
Different spellings
in different models
for the same operation

53. Checklist for the Requirements Review (2)
Syntactical check of the models
Check for consistent naming of classes, attributes, methods in different subsystems
Identify dangling associations (“pointing to nowhere”)
Identify double- defined classes
Identify missing classes (mentioned in one model but not defined anywhere)
Check for classes with the same name but different meanings
One problem with modeling:
We describe a system model with many different views (class diagram, use cases, sequence diagrams, state charts)
We need to check the equivalence of these views
Don’t rely on CASE tools for these checks
Many of the existing tools don’t do these checks for you

54. Omissions in some UML Diagrams
Class Diagram
League
Owner
League 1 *
Attributes
Attributes
Operations
Operations
Missing
Association
(Incomplete
Analysis?)
Attributes
Operations
Tournament_
Boundary
Missing class
(The control object
Announce_Tournament
is mentioned in the
sequence diagram)
Tournament
Attributes
Operations
Player
Match * *
Attributes
Attributes
Operations
Operations

55. When is a Model Dominant?
Object model:
The system has classes with nontrivial states and many relationships between the classes
Dynamic model:
The model has many different types of events: Input, output, exceptions, errors, etc.
Functional model:
The model performs complicated transformations (eg. computations consisting of many steps).
Which model is dominant in these applications?
Compiler
Database system
Spreadsheet program

56. Examples of Dominant Models
Compiler:
The functional model is most important
The dynamic model is trivial because there is only one type input and only a few outputs
Is that true for IDEs?
Database systems:
The object model most important
The functional model is trivial, because the purpose of the functions is to store, organize and retrieve data
Spreadsheet program:
The functional model most important
The dynamic model is interesting if the program allows computations on a cell
The object model is trivial.
Compiler:
The functional model most important. The compiled program must execute correctly if the input was a correct program.
The dynamic model is trivial because there is only one type input and only a few outputs.
Database systems:
The object model most important.
The functional model is trivial, because the purpose of the functions is to store, organize and retrieve data.
Spreadsheet program:
The functional model most important.
The dynamic model is interesting if the program allows computations on a cell.
The object model is trivial, because the spreadsheet values are trivial and cannot be structured further. The only interesting object is the cell.

57. Requirements Analysis Document Template
1. Introduction
2. Current system
3. Proposed system
3.1 Overview
3.2 Functional requirements
3.3 Nonfunctional requirements
3.4 Constraints (“Pseudo requirements”)
3.5 System models
3.5.1 Scenarios
3.5.2 Use case model
3.5.3 Object model
Data dictionary
Class diagrams
3.5.4 Dynamic models
3.5.5 User interfae
4. Glossary

58. Section 3.5 System Model 3.5.1 Scenarios
- As-is scenarios, visionary scenarios
3.5.2 Use case model
- Actors and use cases
3.5.3 Object model
- Data dictionary
- Class diagrams (classes, associations, attributes and operations)
3.5.4 Dynamic model
- State diagrams for classes with significant dynamic behavior
- Sequence diagrams for collaborating objects (protocol)
3.5.5 User Interface
- Navigational Paths, Screen mockups

59. Requirements Analysis Questions
1. What are the transformations?
Create scenarios and use case diagrams
- Talk to client, observe, get historical records
Functional Modeling
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?
Object Modeling
The textbook has a relatively elaborate dynamic model for a programmable thermostat. To get the concept through to you and to show the relation to the object model, I would like to use an even simpler example: The movement of a toy train.
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.
Dynamic Modeling

60. Summary
In this lecture, we reviewed the construction of the dynamic model from use case and object models. In particular, we described:
Sequence and statechart diagrams for identifying new classes and operations.
In addition, we described the requirements analysis document and its components

61. Backup Slides

62. Verification vs Validation of models
fMS
MSystem
System
Design
fMD
MObject
Object
Design
MImpl
fImpl
Implemen-
tation fR R
fMA
MAnalysis
Analysis
Validation
Verification
Verification
Verification M M fM I I R R fR

63. Modeling Concurrency of Events
Two types of concurrency:
1. System concurrency
The overall system is modeled as the aggregation of state diagrams
Each state diagram is executing concurrently with the others.
2. Concurrency within an object
An object can issue concurrent events
Two problems:
Show how control is split
Show how to synchronize when moving to a state without object concurrency
Concurrency is an important aspect any application for two reasons:
Maintainability: If two classes are really concurrent, that means, they are not related to each other, and they can be designed and developed completely independently from each other.
Improved Performance: Concurrency also means in many cases a possible source for fast response time. If methods can be executed in parallel, and not in serial fashion, the systems response time will be better.
Concurrency within a state of a single object arises
when the object can be paritioned into subsets of attributes, each of which has its own subdiagram.
In this case, the state of the object comprises one state from each subdiagram. Note that these subdiagrams don’t have to be independent. The same event can cause state transitions in more than one subdiagram.
Examples of concurrency within an object: A dispenser machine, that simultaneously dispenses cash and ejects the card.
Often concurrency within an object is discovered after the object has been identified. It might be the source for iterating on the object identification and question if there are not two separate objects in the problem that are worth modeling.
1. System concurrency
The overall system is modeled as the aggregation of state diagrams, one for each object.
Each state diagram is executing concurrently with the others.
2. Concurrency within an object
An object can issue concurrent events
In this case we can partition a state into subsets of states (attributes and links)
The state of the object then consists of a set of states: one state from each subset
In the UML notation, the state of an object is divided into subdiagrams
Two issues
Show how control is split
Show how to synchronize when moving to a state without object concurrency

64. Example of Concurrency within an Object
Splitting control
Synchronization
Emitting
do/Dispense
Cash
Cash taken
Ready
Concurrency might be detected within a single object. This sometimes means that our overall decomposition of the system or our initial object identification was too coarse grain.
If there is concurrency, the first question an analyst should ask: What two objects are hidden in the currently modeled single objects? In many cases, uncovering these two yet unknown classes will lead to new insights in the application or result in a better taxonomy or object model.
In some cases, the object is inherently not further decomposable. But even in this case, the discussion of concurrency is very important at analysis level, because it will have important ramifications during system design (mappability of the concurrent methods on two different processors due to data parallelism, for example) and implementation (choice of programming language that supports light level threads instead of heavy level processes).
Ready
to r
eset
Setting Up
do/Eject
Card
Card taken

65. Is this a good Sequence Diagram?
Smart Card
Onboard Computer
Seat
Establish Connection
Accept Connection
Get SeatPosition
“500,575,300”
The first column is not an actor
It is not clear where the boundary object is
It is not clear where the control object is
Layout problem: The actor is missing. Who is talking to the Smartcard?
(Create Driver actor who inserts Smart Card into Cardreader)
Creation problem: The control object is not created by the interface object (add dashed lifeline until create() call by interface object)
Access problem: The interface object accesses the control object (replace by dashed line)