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  • Goal: Come up with > a domain model (domain specific objects) > 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 => 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.

Ch05lect2 ud Ch05lect2 ud Presentation Transcript

  • Chapter 5, Analysis: Dynamic Modeling
  • 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
  • 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
  • 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.
  • 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.
  • 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
  • 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.
    • 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
  • Sequence Diagram for “Get SeatPosition”
      • 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 Accept Connection Accept Connection Get SeatPosition “ 500,575,300” Smart Card Onboard Computer Seat Establish Connection time
  • 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
  • ARENA Sequence Diagram: Create Tournament :Tournament «new» 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
  • 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
  • Attributes Operations League Attributes Operations Tournament Attributes Operations Player Attributes Operations Match Attributes Operations League Owner 1 * * *
  • 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
  • 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.
  • 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»
  • Attributes Operations League Attributes Operations Tournament Attributes Operations Player Attributes Operations Match Attributes Operations League Owner 1 * * * Attributes Announce_ Tournament_ Control Attributes Operations Tournament_ Boundary createTournament (name, maxp)
  • 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
  • UML Statechart Diagram Notation
    • 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.
    Event( attr ) [condition]/action entry /action exit/action do/Activity Event with parameters attr Guard condition Action Event Name of State Actions and Activities in State State1 State2
  • Example of a StateChart Diagram do/Make change do/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
  • 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
  • Activity Diagrams
    • An activity diagram is useful to depict the workflow in a system
  • Activity Diagrams allow to model Decisions Decision
  • Activity Diagrams can model Concurrency
    • Synchronization of multiple activities
    • Splitting the flow of control into multiple threads
    Synchronization Splitting
  • 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
  • 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).
  • 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
  • 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
  • Examples for syntactical Problems
    • Different spellings in different UML diagrams
    • Omissions in diagrams
  • Different spellings in different UML diagrams UML Sequence Diagram UML Class Diagram Attributes Operations League Attributes Operations Tournament Attributes Operations Player Attributes Operations Match Attributes Operations League Owner 1 * * * Attributes Operations Tournament_ Boundary Attributes makeTournament (name, maxp) Announce_ Tournament_ Control createTournament (name, maxp) Different spellings in different models for the same operation
  • 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
  • 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
  • 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.
  • 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
  • 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
    • 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
  • 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.