Unit 2(advanced class modeling & state diagram)

2

Example – Car

https://sites.google.com/a/cmrit.ac.in/manoj-c5559/

UNIT – 2: ADVANCED CLASS MODELING, STATE MODELING:

Advanced object and class concepts; Association ends; N-ary associations; Aggregation; Abstract classes; Multiple inheritance; Metadata; Reification; Constraints; Derived data; Packages; Practical tips.

State Modeling: Events, States, Transitions and Conditions; State diagrams; State diagram behaviour; Practical tips.

Advanced object and class concepts

Enumerations

Multiplicity

Scope

Visibility

Enumeration Data type - a set of values together with a set of operations on those

values

To define a new simple data type, called enumeration type, we need 2 things:

A name for the data type

A set of values for the data type

enum {FALSE, TRUE};enum rank {TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT,

NINE, TEN, JACK, QUEEN, KING, ACE};enum colors {BLACK, BLUE, GREEN, CYAN, RED};

The values are written in all caps because they are constants

EnumerationsWhen constructing a model, we should carefully note enumerations,

because they often occur and are important to users.

Enumerations are also significant for an implementation; we may display the possible values with a pick list.

Do not use a generalization to capture the values of an Enumerated attribute.

An Enumeration is merely a list of values; generalization is a means for structuring the description of objects.

Enumerations

In the UML an enumeration is a data type.

The second section lists the enumeration values.

Eg: Boolean type= { TRUE, FALSE}

ScopeScopeUML specifies two types of scope for members: instance and classifier.

Classifier members are commonly recognized as “static” in many programming languages. The scope is the class itself.Attribute values are equal for all instancesMethod invocation does not affect the instance’s state

Instance members are scoped to a specific instance.Attribute values may vary between instancesMethod invocation may affect the instance’s state (i.e., change

instance’s attributes)To indicate a classifier scope for a member, its name must be underlined.

Otherwise, instance scope is assumed by default.

11

Scope

Individual member data (attributes) may have either class scope or instance scope.

Class scope - A single copy of an attribute is shared by all instances of a class. In UML you underline the attribute to indicate class scope:

productCount : int

Instance scope - Each instance of a class would have its own copy of the attribute. All attributes have instance scope by default.

12

Scope examples

Visibility

Visibility refers to the ability of a method to reference a feature from another class and has the possible values of public, protected & private.

Public—Visible anywhere that the class in which it appears is visible; denoted by +.

Package—Visible anywhere in the package containing the class in which it appears; denoted by ~.

Protected—Visible in the class in which it appears and all its sub-classes; denoted by #.

Private—Visible only in the class in which it appears; denoted by -

Restricting visibility is the same as restricting accessibility.

VisibilityThe UML denotes visibility with a prefix

“+” public

“-” private

“#” protected

“~” package

15

Visibility Example

An n-ary association is like a common (binary) association, except that more than two association roles involved in it.

The UML symbol for n-ary associations is a diamond with lines connecting to related classes. If the association has a name, it is written in italics next to the diamond.

N-ary Association

Class1 Class2

Class3

N-aryassociation

Ternaryassociation

N-ary Associations

Associations can connect more than one classNotation:

Student Advisor

Major

N-ary Associations

datetrainNo

TraincarriageNo

seatNo

Seat

nametitle

Passenger

Reservation

1 1..*

1..*

N-ary Associations

We may occasionally encounter n-ary associations (association among 3 or more classes).

But we should try to avoid n-ary associations- most of them can be decomposed into binary associations, with possible qualifiers and attributes.

20

N-ary Association

21

N-ary Association (cont’d)

decompose

22

AggregationA special form of association that models a whole-part relationship between

an aggregate (the whole) and its parts.Models a “is a part-part of” relationship.

The aggregation association represents the part-whole relation between classes.Denoted by a solid diamond and linesDiamond attaches to the aggregate (whole) while lines attach to the partsMay have all association adornments

Whole Part

Car Door House

23

Aggregation (cont.)

Aggregation tests: Is the phrase “part of” used to describe the relationship?

A door is “part of” a carAre some operations on the whole automatically applied to its

parts? Move the car, move the door.

Are some attribute values propagated from the whole to all or some of its parts? The car is blue, therefore the door is blue. A door is part of a car. A car is not part of a door.

Car Door House

Whole Part

Aggregation

*Pizza Order

Slice

Crust

Sauce Serving

Cheese Serving

Topping Serving

25

CompositionComposition is a form of aggregation with strong

ownership and coincident lifetime of the parts by the whole; the part object may belong to only one whole – the parts are usually expected to live and die with the whole. (usually, any deletion of the whole is considered to cascade to the parts}{filled diamond}

Aggregation and Composition

Aggregation is a special form of association that specifies a whole-part relationship between the aggregate (the whole) and a component (the part); aggregation is the part-of relationship. { it is a special form of association in which a collection of objects, each having an independent existence, is associated with an single object} {unfilled diamond}

Composition is a form of aggregation with strong ownership and coincident lifetime of the parts by the whole; the part object may belong to only one whole – the parts are usually expected to live and die with the whole. (usually, any deletion of the whole is considered to cascade to the parts}{filled diamond}

Metadata

The term "meta" comes from a Greek word that denotes something of a higher or more fundamental nature. Metadata, then, is data about other data.

The term refers to any data used to aid the identification, description and location of networked electronic resources

Defining Metadata

Librarians equate it with a complete bibliographic record

Information technologists equate it to database schema or definitions of the data elements

Archivists include context information, restrictions and access terms, index terms, etc.

Metadata

Metadata is data that describes other data. For example, a class definition is a metadata.

Models are inherently metadata, since they describe the things being modeled (rather than being the things).

Many real-world applications have metadata, such as parts catalogs, blueprints, and dictionaries. Computer-languages implementations also use metadata heavily.

Derived Data

A derived element is a function of one or more elements, which in turn may be derived.

A derived element is redundant, because the other elements completely determine it.

Ultimately, the derivation tree terminates with base elements. Classes, associations, and attributes may be derived. The notation for a derived element is a slash in front of the element

name along with constraint that determines the derivation.

Derived Data

Employee

Basic Pay

/gross pay

Packages

A package is a group of elements (classes, association, generalization, and lesser packages) with a common theme.

A package partitions a model making it easier to understand and manage. Large applications my require several tiers of packages.

Packages form a tree with increasing abstraction toward the root, which is the application, the top-level package.

Notation for package is a box with a tab.

Customer Order

Sales

When to use Package

To create a overview of a large set of model elements

To organize a large model

To group related elements

State Modeling State model describes the sequences of operations that occur in

response to external stimuli.

The state model consists of multiple state diagrams, one for each class with temporal behavior that is important to an application.

The state diagram is a standard computer science concept that relates events and states.

Events represent external stimuli and states represent values objects.

Elements of State Diagrams

The basic elements of state diagrams are

Events – An event is an occurrence at a point in time

states – the state in which the object finds itself at any moment

transitions – take the object from one state to another

actions – take place as a result of a transition

EventsAn event is an occurrence at a point in time such as –

User presses left button

Indigo flight departs from Mumbai

An event happens instantaneously with regard to time scale of an application.

One event may logically precede or follow another, or the two events may be unrelated (concurrent; they have no effect on each other).

Types of Events

An event may be one of 3 types

Signal event

Time event

Change event

Signal EventA signal is an explicit one-way transmission of information from one

object to another.

An object sending a signal to another object may expect a reply, but the reply is a separate signal under the control of the second object, which may or may not choose to send it.

A signal event is the event of sending or receiving a signal (concern about receipt of a signal).

The difference between signal and signal eventa signal is a message between objects

a signal event is an occurrence in time.

Time EventTime event is an event caused by the occurrence of an absolute

time or the elapse of a time interval.UML notation for an absolute time is the keyword when

followed by a parenthesized expression involving time.The notation for a time interval is the keyword after followed

by a parenthesized expression that evaluates to a time duration.

when (date = jan 1, 2000 )

Change EventA change event occurs whenever a specified condition is met

Event name is specified as keyword whenParameter list is a Boolean expressionThe event occurs when both of the following conditions are met,

irrespective of the order when they happen The expression evaluates to true The object is in the required state

when (battery power < lower limit )

when (tire pressure < minimum pressure )

StatesState is a condition or situation during the life of an object within

which it performs some activity, or waits for some eventsThe objects in a class have a finite number of possible states.Each object can be in one state at a time.A state specifies the response of an object to input events. At any given point in time, the system is in one state.It will remain in this state until an event occurs that causes it to

change state.

Event vs. States Event represents points in time.State represents intervals of time.

States

A state is when a system is:

Doing something – e.g., heating oven, mixing ingredients, accelerating engine,

Waiting for something to happen – Waiting for user to enter password, waiting for sensor reading.

Eg:

power turned on power turned off power turned on

Time Powered

Not powered

A state corresponds to the interval between two events received by an object.

The state of an object depends on past events.

Basic UML Syntax

A state is drawn with a round box, with three compartments fornamestate variables (if any)actions to be performed

Name

state variables

actions

sometimesleft out whenempty

Transitions

A transition is a relationship between two states indicating that an object in the first state will enter the second state.

A transition is an instantaneous change from one state to another.

The transition is said to fire upon the change from the source state to target state.

A guard condition must be true in order for a transition to occur.

A guard condition is checked only once, at the time the event occurs, and the transition fires if the condition is true.

51

TransitionA directed relationship between two states.

Contains five parts

Source state - current state before transition fires. Event trigger - external stimulus that has the potential to

cause a transition to fire. Guard condition - a condition that must be satisfied before

a transition can fire. Target state - new state after transition fires.

Basic UML Syntax

A transition is drawn with an arrow, possibly labeled withevent causing the

transactionguard conditionAction to perform

AnEvent [guard] / SomeAction

53

Idle

Initial State

Running

Final State

State

Transition

53

Billing Example

State Diagrams show the sequences of states an object goes through during its life cycle in response to stimuli, together with its responses and actions; an abstraction of all possible behaviors.

Unpaid

Start End

PaidInvoice created paying Invoice destroying

AddParticipant / Set count = 0

cancel seminar

event action, taken duringtransition

Setup

do/initialize seminarAvailable

do/initialize seminar

Full

do/finalize seminar

[ count = 20 ]

guard

Canceled

do/refund payments

cancel seminar

multipleexits

cancelseminar

aktivity, carried outwhile in that state

Actions

Action

is an executable atomic computation

includes operation calls, the creation or destruction of another object, or the sending of a signal to an object

associated with transitions and during which an action is not interruptible -- e.g., entry, exit

Predefined Action Labels

“entry/” identifies an action, specified by the corresponding action expression,

which is performed upon entry to the state (entry action)“exit/”

identifies an action, specified by the corresponding action expression, that is performed upon exit from the state (exit action)

“do/” identifies an ongoing activity (“do activity”) that is performed as long as

the modeled element is in the state or until the computation specified by the action expression is completed (the latter may result in a completion event being generated).

“include/” is used to identify a submachine invocation. The action expression

contains the name of the submachine that is to be invoked.

State Diagrams notation

PaidUnpaidpaying

Invoice created

Invoice destroyed

name

state

final stateInitial state

transition

event

Here’s a simple example SD for a washing machine.

State

Transition

Condition

Action

60

A condition is typically some kind of event, e.g.:•Signal•Arrival of an object (data/material),•Etc…

Condition

Action

An action is the appropriate output or response to the event, e.g.:•Signal or message•Transfer of an object,•Calculation,•Etc…

State Diagrams (Traffic light example)

Yellow

Red

Green

Traffic LightState

Transition

Event

Start

Transitions

xx yyevent [guard] | action

The event that triggers the transition

Conditions that must be met for the transition to take place

The action that takes place when the transition is taken

Initial and Final States

An example:

At Work At Homego home

go to work

die die

64

State Diagrams

65

66

67

68

Phone Example

digit dialed (n)[incomplete]

Dialing Connecting

busy

connected

digit dialed (n)[valid] / connectdigit dialed (n)

[invalid]

Invalid

Ringing

Busy

68

69

States of Garment (Garments system)

Garment ordered

Material ordered

Material delivered

Marked out for cutting

Cut

Marked out for sewing

Sewn

Marked out for finishing

Finished

Deleted

71

State Diagrams

A state diagram describes the behaviour of a system, some part of a system, or an individual object.

At any given point in time, the system or object is in a certain state. Being in a state means that it is will behave in a specific way in

response to any events that occur.

Some events will cause the system to change state. In the new state, the system will behave in a different way to

events.

A state diagram is a directed graph where the nodes are states and the arcs are transitions.

72

Using Microsoft Visio

Visio can be used to draw UML diagrams It is component of Microsoft Office

73

Using Microsoft Visio (continued)

Available Sets of Shapes in the UML Collection

Activity Diagrams

Collaboration Diagrams

Components

Deployment Diagrams

Sequence Diagrams

State Diagrams (Statecharts)

Static Structures (shown) – include Packages and Classes

Use Case Diagrams

74

Using Microsoft Visio (concluded)

UML symbols can be displayed as icons with names or icons with descriptions

Both forms of display for the Use Case shape set are shown

Now, on to the demo!

75

start state

stop state

transition from one state to another

self-transition (no change of state)

event [guard] / action transition label (each of the three parts is optional)

state

The Inheritance Mechanism

Means of deriving new class from existing classes, called base classes

Reuses existing code eliminating tedious, error prone task of developing new code

Derived class developed from base by adding or altering code

Multiple Inheritance

A derived class with several base classes is known as multiple inheritance

Multiple inheritance permits a class to have more than one super class and to inherit features from all parents.

We can mix information from 2 or more sources.

This is a more complicated from of generalization than single inheritance.

The advantage of multiple inheritance is greater power in specifying classes and an increased opportunity for reuse.

The disadvantage is a loss of conceptual and implementation simplicity.

Credit Cards - Single Inheritance

Same basic features

Each is a little different

Voice Mail - Multiple Inheritance

Voice mail has featuresof both mail and phone

What Is A Constraint

A condition or restriction (a Boolean expression) expressed in natural language text or in a machine readable language for the purpose of declaring some of the semantics of an element

Some are predefined in UML (“xor”), others may be user-defined

OCL (Object Constraint Language) is a predefined language for writing constraints

81

Constraints

These are functional relation between entities of an object model.

Entity includes objects, classes, attributes, links and associations.

A constraint restricts the values that entities can assume.Simple constraints may be placed in object models and

complex may be in functional model.

82

Employee

salary

boss

{ salary < = boss.salary }

Window

Lengthwidth

{ 0.8 <= length / width < = 1.5 }

Constraints on objects