Chapter 2: Modeling with UML - 2

A Medical Clinic Example “A patient calls the clinic to make an appointment for a yearly checkup. The receptionist finds the nearest empty time slot in the appointment book and schedules the appointment for that time slot” “A patient can request or discuss medication with a doctor” “A patient can make payment through the system” <includes>, <extends>, generalization Online tutorial and Use case modeling tips

Use Case Diagrams: Summary Use case diagrams represent external behavior All use cases need to be described for the model to be useful. An Actor is a role of an object or objects outside of a system that interacts directly with it as part of a coherent work unit (a use case) <<includes>> and <<extends>> allow common fragments of use cases to be pulled out into a separate use cases <<includes>> is like a “use case subroutine” <extends>> is an alternative course of action

Class Diagrams TarifSchedule Trip Enumeration getZones() Price getPrice(Zone) zone:Zone Price: Price * * Class diagrams represent the structure of the system. Used during requirements analysis to model problem domain concepts during system design to model subsystems and interfaces during object design to model classes.

Classes Name Signature Attributes Operations Table zone2price Enumeration getZones() Price getPrice(Zone) TarifSchedule Name zone2price getZones() getPrice() TarifSchedule Attributes Signature Operations TarifSchedule A class represent a concept A class encapsulates state (attributes) and behavior (operations). Each attribute has a type. Each operation has a signature. The class name is the only mandatory information.

tarif_1974:TarifSchedule Instances tarif_1974:TarifSchedule zone2price = { {‘1’, .20}, {‘2’, .40}, {‘3’, .60}} An instance represents a phenomenon. The name of an instance is underlined and can contain the class of the instance. The attributes are represented with their values.

Actor vs Instances What is the difference between an actor , a class and an instance? Actor: An entity outside the system to be modeled, interacting with the system (“Passenger”) Class: An abstraction modeling an entity in the problem domain, must be modeled inside the system (“User”) Object: A specific instance of a class (“Joe, the passenger who is purchasing a ticket from the ticket distributor”).

Associations * * Associations denote relationships between classes. TarifSchedule TripLeg Enumeration getZones() Price getPrice(Zone) Price Zone * * Associations denote relationships between classes. The multiplicity of an association end denotes how many objects the source object can legitimately reference.

1-to-1 and 1-to-many Associations Country capital name:String name:String One-to-one association Point * Polygon x: Integer y: Integer draw() One-to-many association

Many-to-Many Associations Lists * * Company StockExchange tickerSymbol * Lists 1 A stock exchange lists many companies each of them uniquely identifed by a ticker symbol used at that stock exchange. A company can be listed on more than one stock exchange, using the same ticker symbol. Mercedes Benz is an example for a company listed on more than one stock exchange: Frankfurt and NYSE. Does it have two different Ticker symbols? Something not clear here: What happens if the company cannot have the same ticker symbol on two different stock exchanges? Company StockExchange tickerSymbol SX_ID qualifier

From Problem Statement To Object Model oblem Statement: A stock exchange lists many companies. Each company is uniquely identified by a ticker symbol Class Diagram: Company StockExchange * * Lists tickerSymbol

From Problem Statement to Code : A stock exchange lists many companies. Each company is identified by a ticker Symbol Class Diagram: * * StockExchange Company Lists tickerSymbol Java Code public class StockExchange { private Vector m_Company = new Vector(); }; public class Company { public int m_tickerSymbol; private Vector m_StockExchange = new Vector(); };

Aggregation An aggregation is a special case of association denoting a “consists of” hierarchy. The aggregate is the parent class, the components are the children class. A solid diamond denotes composition, a strong form of aggregation where components cannot exist without the aggregate. Exhaust system Muffler diameter Tailpipe 1 0..2 Exhaust system 1 0..2 Muffler Tailpipe diameter diameter TicketMachine 3 ZoneButton

Inheritance Button ZoneButton CancelButton The children classes inherit the attributes and operations of the parent class. Inheritance simplifies the model by eliminating redundancy.

Class Relationships Our class diagram has the following kinds of relationships. association -- a relationship between instances of the two classes. There is an association between two classes if an instance of one class must know about the other in order to perform its work. In a diagram, an association is a link connecting two classes. aggregation -- an association in which one class belongs to a collection. An aggregation has a diamond end pointing to the part containing the whole. In our diagram, Order has a collection of OrderDetails. generalization -- an inheritance link indicating one class is a superclass of the other. A generalization has a triangle pointing to the superclass. Payment is a superclass of Cash, Check, and Credit.

Composition and aggregation Associations in which an object is part of a whole are aggregations. Composition is a strong association in which the part can belong to only one whole -- the part cannot exist without the whole. Composition is denoted by a filled diamond at the whole end. This diagram shows that a BoxOffice belongs to exactly one MovieTheater. Destroy the MovieTheater and the BoxOffice goes away! The collection of Movies is not so closely bound to the MovieTheater.

Without qualification Qualifiers Directory File filename Without qualification 1 * With qualification Directory File 0…1 1 filename Qualifiers can be used to reduce the multiplicity of an association.

Object Modeling in Practice: Class Identification Foo Foo, by providing his customerId, can deposit, withdraw, and get balance from his account. CustomerId Deposit() Withdraw() GetBalance() Class Identification: Name of Class, Attributes and Methods

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

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

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

Practice Object Modeling: Iterate, Categorize! Account Amount Deposit() Withdraw() GetBalance() CustomerId AccountId Bank Name Customer Name * * Has CustomerId Savings Account Withdraw() Checking Account Withdraw() Mortgage Account Withdraw()

Packages A package is a UML mechanism for organizing elements into groups (usually not an application domain concept) Packages are the basic grouping construct with which you may organize UML models to increase their readability. A complex system can be decomposed into subsystems, where each subsystem is modeled as a package DispatcherInterface Notification IncidentManagement

A Class Diagram Example A customer order from a retail catalog. Identify the major classes Customer, Order How to pay? – Payment One order can have multiple types of merchandises. For a merchandise, depending on its quantity, the unit price (or tax) for that order may be different….. See Practical UML™: A Hands-On Introduction More complex – Shipping? Stock? Account? Bank?

Class Diagram Summary Class diagrams represent the structure of the system Name, attribute, operation Class vs. instance Association, aggregation, composition, generalization Multiplicity

UML sequence diagrams Used during requirements analysis selectZone() pickupChange() pickUpTicket() insertCoins() Passenger TicketMachine Used during requirements analysis To refine use case descriptions to find additional objects (“participating objects”) Used during system design to refine subsystem interfaces Classes are represented by columns Messages are represented by arrows Activations are represented by narrow rectangles Lifelines are represented by dashed lines

Nested messages Dataflow Passenger TarifSchedule Display ZoneButton selectZone() lookupPrice(selection) price Dataflow displayPrice(price) …to be continued... The source of an arrow indicates the activation which sent the message An activation is as long as all nested activations Horizontal dashed arrows indicate data flow Vertical dashed lines indicate lifelines

…continued from previous slide... Iteration & condition Passenger …continued from previous slide... CoinIdentifier Display CoinDrop ChangeProcessor * insertChange(coin) lookupCoin(coin) price Iteration displayPrice(owedAmount) Condition [owedAmount<0] returnChange(-owedAmount) …to be continued... Iteration is denoted by a * preceding the message name Condition is denoted by boolean expression in [ ] before the message name

Creation and destruction Passenger …continued from previous slide... ChangeProcessor Creation Ticket createTicket(selection) print() Destruction free() Creation is denoted by a message arrow pointing to the object. Destruction is denoted by an X mark at the end of the destruction activation. In garbage collection environments, destruction can be used to denote the end of the useful life of an object.

Sequence Diagram: A Example Making an online hotel reservation

Sequence Diagram Summary UML sequence diagram represent behavior in terms of interactions. Useful to find missing objects. Time consuming to build but worth the investment. Complement the class diagrams (which represent structure).

Represent behavior as states and transitions State Chart Diagrams State Initial state Event Transition Final state Represent behavior as states and transitions

State Chart Diagrams -- Example A screen savor program

Activity Diagrams An activity diagram shows flow control within a system An activity diagram is a special case of a state chart diagram in which states are activities (“functions”) Two types of states: Action state: Cannot be decomposed any further Happens “instantaneously” with respect to the level of abstraction used in the model Activity state: Can be decomposed further The activity is modeled by another activity diagram

Statechart Diagram vs. Activity Diagram Statechart Diagram for Incident (similar to Mealy Automaton) (State: Attribute or Collection of Attributes of object of type Incident) Event causes State transition Active Inactive Closed Archived Incident- Documented Incident- Handled Incident- Archived Activity Diagram for Incident (similar to Moore (State: Operation or Collection of Operations) Triggerless Transition Completion of activity causes state transition

Activity Diagram: Modeling Decisions

Activity Diagrams: Modeling Concurrency Synchronization of multiple activities Splitting the flow of control into multiple threads Splitting Synchronization

Activity Diagrams: Swimlanes Actions may be grouped into swimlanes to denote the object or subsystem that implements the actions. Dispatcher Allocate Resources Open Coordinate Archive Incident Resources Incident FieldOfficer Document Incident

What should be done first? Coding or Modeling? It all depends…. Forward Engineering: Creation of code from a model Greenfield projects Reverse Engineering: Creation of a model from code Interface or reengineering projects Roundtrip Engineering: Move constantly between forward and reverse engineering Useful when requirements, technology and schedule are changing frequently

UML Summary UML provides a wide variety of notations for representing many aspects of software development Powerful, but complex language Can be misused to generate unreadable models Can be misunderstood when using too many exotic features For now we concentrate on a few notations: Functional model: Use case diagram Object model: class diagram Dynamic model: sequence diagrams, statechart and activity diagrams

Problems with UML Semi-formal Go directly to the class/objects – a low level. Not good at express temporal information – StateChart Term paper topic for graduate students

Additional Slides

Models for Plato’s and Aristotle’s Views of Reality Material reality is a second-class subordinate type of reality. The first-class type is a “form” Forms lie behind every thing or in the world. Forms can be abstract nouns like “beauty” or “mammal” or concrete nouns like “tree” or “horse”. There is an important difference between the world of forms and particulars. Forms are nonmaterial, particulars are material. Forms are permanent and changeless. Particulars are changing. Forms can be acquired intellectually through a “dialectic” process that moves toward the highest understanding of reality through the interaction of questions and answers. Aristotle accepted the reality of Forms as nonmaterial entities. However, he could not accept Plato’s idea, that these Forms were not real. Instead of two separate worlds, one for Forms and one for Particulars, Aristotle had only one world, a world of particular things. Particular things according to Aristotle have a certain permance about them, even while they are subject to change: A tree changes colors without ceasing to be a tree. A horse grows in size without ceasing to be a horse. What is the root of this permancence? It is the thing’s internal form, which minds detect, when they penetrate beyond the thing’s changing attributes. So for Aristotle, reality is thus made up of particular things that are each composed of form antdn matter.. lato’s model of reality (UML class diagram). Reality consists of many particular things and many forms. Note, that forms are not abstract classes that need to be instantiated. Forms such as beauty really exist independent from a particular, that is they can be instantiated by themself. Aristotle’s model of reality: Reality consists of many particular things called substances. Each substance is composed of form and matter. Beauty is real but it does not exist on its own, it is always part of a really existing thing called the substance. Using UML, we can illustrate Platon’s and Aristotle’s viewpoints very easily and see their differences as well

Model for Plato’s View of Reality Material reality is a second-class subordinate type of reality. The first-class type is a “form” Forms lie behind every thing or in the world. Forms can be abstract nouns like “beauty” or “mammal” or concrete nouns like “tree” or “horse”. There is an important difference between the world of forms and particulars. Forms are nonmaterial, particulars are material. Forms are permanent and changeless. Particulars are changing. Forms can be acquired intellectually through a “dialectic” process that moves toward the highest understanding of reality through the interaction of questions and answers. lato’s model of reality (UML class diagram). Reality consists of many particular things and many forms. Note, that forms are not abstract classes that need to be instantiated. Forms such as beauty really exist independent from a particular, that is they can be instantiated by themself. Aristotle’s model of reality: Reality consists of many particular things called substances. Each substance is composed of form and matter. Beauty is real but it does not exist on its own, it is always part of a really existing thing called the substance.

Model Aristotle’s Views of Reality Aristotle accepted the reality of Forms as nonmaterial entities. However, he could not accept Plato’s idea, that these Forms were not real. Instead of two separate worlds, one for Forms and one for Particulars, Aristotle had only one world, a world of particular things. Particular things according to Aristotle have a certain permance about them, even while they are subject to change: A tree changes colors without ceasing to be a tree. A horse grows in size without ceasing to be a horse. What is the root of this permancence? It is the thing’s internal form, which minds detect, when they penetrate beyond the thing’s changing attributes. So for Aristotle, reality is thus made up of particular things that are each composed of form antdn matter.. lato’s model of reality (UML class diagram). Reality consists of many particular things and many forms. Note, that forms are not abstract classes that need to be instantiated. Forms such as beauty really exist independent from a particular, that is they can be instantiated by themself. Aristotle’s model of reality: Reality consists of many particular things called substances. Each substance is composed of form and matter. Beauty is real but it does not exist on its own, it is always part of a really existing thing called the substance.

Comparison of Plato’s and Aristotle’s Views lato’s model of reality (UML class diagram). Reality consists of many particular things and many forms. Note, that forms are not abstract classes that need to be instantiated. Forms such as beauty really exist independent from a particular, that is they can be instantiated by themself. Aristotle’s model of reality: Reality consists of many particular things called substances. Each substance is composed of form and matter. Beauty is real but it does not exist on its own, it is always part of a really existing thing called the substance.