2. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2
Outline of the Lecture
• Dynamic modeling
• Interaction Diagrams
• Sequence diagrams
• Collaboration diagrams
• State diagrams
• Activity diagrams (UD: interestingly, our book continues to ignore their
significance; considers as a special case of State diagrams!)
• Requirements analysis model validation
3. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 3
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:
• Activity lines in sequence diagrams are candidates for
objects
• Actions and activities in state chart diagrams are
candidates for public operations in classes
4. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 4
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
• Activity diagrams: Model the (complex) logic (business
rules) captured by a use case
• Purpose:
• Detect and supply operations for the object model.
5. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 5
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.
6. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 6
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
7. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 7
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.
8. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 8
• 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?
An Example
9. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 9
Sequence Diagram for “Get SeatPosition”
Establish Connection
Accept Connection
Accept Connection
Get SeatPosition
“500,575,300”
Smart Card Onboard Computer Seat
Establish Connection
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.
time
10. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 10
Heuristics for Sequence Diagrams
• 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.
• 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
11. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 11
:Tournament
«new»
ARENA Sequence Diagram: Create Tournament
League
Owner
:Tournament
Boundary
newTournament
(league)
:Announce
Tournament
Control
«new»
setName(name)
setMaxPlayers
(maxp)
commit()
createTournament
(name, maxp)
checkMax
Tournament()
create
Tournament
(name, maxp)
:Arena :League
12. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 12
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
13. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 13
Attributes
Operations
League
Attributes
Operations
Tournament
Attributes
Operations
Player
Attributes
Operations
Match
Attributes
Operations
League Owner
1 *
* *
14. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 14
Attributes
Operations
League
Attributes
Operations
Tournament
Attributes
Operations
Player
Attributes
Operations
Match
Attributes
Operations
League Owner
1 *
* *
Attributes
Operations
Tournament_
Boundary
Attributes
Operations
Announce_
Tournament_
Control
15. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 15
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
• 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.
16. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 16
Example from the Sequence Diagram
createTournament
(name, maxp)
create
Tournament
(name, maxp)
League
Owner
:Tournament
Boundary
newTournament
(league)
:Announce
Tournament
Control
«new»
setName(name)
setMaxPlayers
(maxp)
commit()
checkMax
Tournament()
:Arena :League
:Tournament
«new»
17. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 17
Attributes
Operations
League
Attributes
Operations
Tournament
Attributes
Operations
Player
Attributes
Operations
Match
Attributes
Operations
LeagueOwner
1 *
* *
Attributes
Operations
Tournament_
Boundary
Attributes
createTournament
(name, maxp)
Announce_
Tournament_
Control
18. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 18
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
19. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 19
UML Statechart Diagram Notation
State1 Event(attr) [condition]/action
entry /action
exit/action
• 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.
do/Activity
State2
Event with parameters attr
Guard
condition
Action
Event
Name of
State
Actions and Activities in State
20. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 20
Example of a StateChart Diagram
do/Make changedo/Dispense item
Idle
[item empty] [select(item)]
[change=0] [change>0]
[change<0]
coins_in(amount) / set balance
cancel / refund coins
Collect Money
coins_in(amount) / add to balance
do/Test item and compute change
21. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 21
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
22. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 22
Activity Diagrams
• An activity diagram is useful to depict the
workflow in a system
Handle
Incident
Document
Incident
Archive
Incident
23. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 23
Activity Diagrams allow to model Decisions
Open
Incident
Notify
Police Chief
Notify
Fire Chief
Allocate
Resources
[fire & highPriority]
[not fire & highPriority]
[lowPriority]
Decision
24. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 24
Activity Diagrams can model Concurrency
• Synchronization of multiple activities
• Splitting the flow of control into multiple threads
Open
Incident
Allocate
Resources
Coordinate
Resources
Document
Incident
Archive
Incident
SynchronizationSplitting
25. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 25
Activity Diagrams: Grouping of Activities
• Activities may be grouped into swimlanes to
denote the object or subsystem that implements
the activities.
Open
Incident
Allocate
Resources
Coordinate
Resources
Document
Incident
Archive
Incident
Dispatcher
FieldOfficer
26. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 26
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).
27. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 27
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
28. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 28
Checklist for a Requirements Review
• Is the model correct?
• A model is correct if it represents the client’s view of
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
29. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 29
Examples for syntactical Problems
• Different spellings in different UML diagrams
• Omissions in diagrams
30. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 30
Attributes
Operations
League
Attributes
Operations
Tournament
Attributes
Operations
Player
Attributes
Operations
Match
Attributes
Operations
LeagueOwner
1 *
* *
Attributes
Operations
Tournament_
Boundary
Attributes
makeTournament
(name, maxp)
Announce_
Tournament_
Control
Different spellings in different UML diagrams
UML Sequence Diagram UML Class Diagram
createTournament
(name, maxp)
Different spellings
in different models
for the same operation
31. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 31
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
32. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 32
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 (e.g.
computations consisting of many steps).
• Which model is dominant in these applications?
• Compiler
• Database system
• Spreadsheet program
33. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 33
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.
34. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 34
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
3.5.3.1 Data dictionary
3.5.3.2 Class diagrams
3.5.4 Dynamic models
3.5.5 User interfae
4. Glossary
35. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 35
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)
- Activity diagrams for complex business rules/logic
3.5.5 User Interface
- Navigational Paths, Screen mockups
36. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 36
1. What are the transformations?
Create scenarios and use case diagrams
- Talk to client, observe, get historical records
2. What is the structure of the system?
Create class diagrams
- Identify objects. Associations between them? Their multiplicity?
- What are the attributes of the objects? Operations 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.
Create activity diagrams
Requirements Analysis Questions
Dynamic Modeling
Functional Modeling
Object Modeling
37. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 37
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.
• Activity diagrams for describing complex
business rules/logic inside operations.
• In addition, we described the requirements
analysis document and its components.
Editor's Notes
Goal: Come up with
&gt; a domain model (domain specific objects)
&gt; a taxonomy (class hierarchy)
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 =&gt; 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
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.
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).
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.
Let’s assume, before we formulated the sequence diagram on the last slide,
ARENA’s object model contained the objects
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
createTournament is a public operation offered by Announce_Tournament_Control
This is the corresponding view in the UML class diagram:
createTournament is a public operation offered by Announce_Tournament_Control
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.
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.
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!
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.
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.
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
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
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
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.
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.