OOMD Module2 Dynamic Modelling

7/26/2019 OOMD Module2 Dynamic Modelling

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Module 2: Dynamic modeling

Vidhya P.M


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Dynamic Modeling

First examine the system at a single moment of time.

Then examine changes to objects and theirrelationships over time.

Those aspects of a system that are concerned with

time and changes are dynamic model, in contrast withstatic or object model.

Control is the aspect of a system that describes thesequences of operations that occur in response to

external stimuli without considering what the operationdo, what they operate on, and how they areimplemented.

Vidhya P.M


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concepts

Eventsrepresent external stimuli

Statesvalues of objects

State diagram


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Events

It is something that happens at a point in time,withnoduration

Anindividualstimulusfromoneobjecttoanotherisanevent.

One event may logically precede or followanother or the two events may be unrelated.

The two events are casually related.

The two events are casually unrelated are saidto be concurrenti.e. they have no effect on eachother.


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An event is a one-way transmission ofinformation from one object to another.

In real world, all objects existconcurrently.

An object sending an event to anotherobject may expect a reply but the reply is

a separate event under the control of thesecond object which may or may notchoose to send it.


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Every event is a unique occurrence, but we groupthem into event classes and give each event class aname to indicate common structure and behavior.

E.g. flight 123 departs from Delhi and flight 321departs from Rome are instances of event classairplane flight departs having attributes airline flight no,city.

The time at which an event occurs is an implicitattribute of all events.


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Vidhya P.M 7

An event conveys information from one

object to another.

Some classes of events may be simply

signals that something has occurred

while other convey data values i.e.

attributes.

Showing attributes is optional.


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Vidhya P.M 8

Airplane flight departs (airline, flight#, city)

Mouse button pushed (button, location)

Input string entered (text)Phone receiver lifted

Digit dialed (digit)

Event classes and attributes


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Vidhya P.M 9

Scenarios and event traces

A scenario is a sequence of events that occurs

during one particular execution of a system.

The scope of a scenario can vary; it mayinclude all events in the system or it may

include only those events generated by certain

objects in the system.


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Vidhya P.M 10

Caller lifts receiver

Dial tone begins

Caller dials digit (5)

Dial tone endsCaller dials digit (5)





Called phone begins ringing

Ringing tone appears in calling phone

Called party answers

Called phone stops ringing

Ringing tone disappears in calling phone

Phones are connected

Called party hangs up

Phones are disconnected

Caller hangs up

Scenario for phone call


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The next step after writing scenario is to identify thesender and receiver objects of each event.

The sequence of events and the objects exchangingevents are shown in event trace diagram.

This diagram shows each object as a vertical line andeach event as a horizontal arrow from the sender toreceiver objects.

Time increases from top to bottom.

Sequences of events are shown not their exact timing.


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Vidhya P.M 12

Event trace for phone call

Caller phone line callee

Caller lifts receiver

Dial tone begins


Dial tone ends


Caller dials digit (4)Caller dials digit (3)



Called phone begins ringing phone rings

answer phone

ringing stops ringing stops

phones are connected phones connectedCallee hangs up

disconnected disconnected

Caller hangs up

twoconcurrentevents


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Vidhya P.M 13

States

It is an abstraction of the attribute values and links ofan object.

Set of values are grouped together into a stateaccording to properties that affect the gross behavior

of the object. A state specifies the response of the object to input

events.

Response is same for all values within the same stateand may be different for values in different states.

Response of an object to an event may include anaction or change of states by the object.


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Vidhya P.M 14

A state has duration

An event separates two states and a

state separates two events.

In defining states we ignore those

attributes that do not affect the behavior

of the objects.


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Vidhya P.M 15

State diagram

It relates events and states.

When an event is received, the next

state depends on the current state as

well as the event; a change of state

caused by an event is called a transition.

State diagram is a graph whose nodes

are states and whose directed arcs are

transitions labeled by event names.


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idle

Timed- out

disconnected

Busy tone

Fast busy tone

Dial tone

dialing

connecting

ringing

connected

Recorded message

On-hook On-hook

Off-hook

Digit(n)

Invalid novalid

routed

Called phone answers

Called phone hangs up

Trunk busy

Num busy

State diagram for phone line


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Vidhya P.M 17

A state diagram describes the behavior of asingle class.

Since all instances of a class have same

behavior they all share the same statediagram as they all share the same classfeatures.

But as each object has its own attribute values

so each object has its own state. Each object is independent of the other

objects and proceeds as its own pace.


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Vidhya P.M 18

Statediagramscanrepresentone-shotlifecyclesorcontinuousloops.

One-shotdiagramsrepresentobjectswithfinitelives.Aone-shotdiagramhasinitialandfinalstates.

Theinitialstateisenteredoncreationofanobject

Entering thefinalstateimpliesdestructionoftheobject.


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stalemate

emat

One-shot

statediagram

Thedynamicmodelisacollectionofstatediagramsthatinteractwitheachotherviasharedevents.Anobjectmodelrepresentsthestaticstructureofasystem,while

dynamicmodelrepresentsthecontrolstructureofasystem.

Ascenarioistoadynamicmodelasaninstancediagramistoanobjectmodel.

White'sturn

black

moves

Black's

turn

checkmate

whitemoves

stale

checkmate

Blackwins

Draw

Whitewins

Start

finalstate(bull'seye)

initialstate(solidcircle)

Oneshot


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Vidhya P.M 20

Conditions

A condition is a Boolean function of

object values.

When Ram goes out in morning( event),

if the temperature is below freezing(

condition), then he puts on his gloves

(next state).

Notation is [condition]


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Example

Starting

entry / start dial tone

exit / end dial tone

Dialing

entry / number.append(n)

dialed (n)

dialed (n)

[number.isValid()]


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Vidhya P.M 22

Operations

An activity is an operation that takes time to complete.

An activity is associated with a state.

Notation do:A within a state box indicates that activity A startson entry to the state and stops on exit.

An action is an instantaneous operation.

An operation is associated with an event. An action represents an operation whose duration is insignificant

compared to the state diagram e.g. disconnect phone line mightbe an action in response to an on_hook event for phone line.

Actions can also represent internal control operations such assetting attributes or generating other events.

The notation for an action is (/) and the name of action, followingthe name of the event that causes it.


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Vidhya P.M 23

Action for pop-up menu

idle Menu visible

Right button down/display menu

Right button up/erase menu

Cursor moved/highlight menu item


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SummaryofNotationforStateDiagramswith

Operations

State1do:activity1

State2do:activity1

Event1 (attributes)[condition1]/action1


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State Chart Diagram vs Sequence Diagram

State chart diagrams help to identify:

Changesto an individual objectover time

Sequence diagrams help to identify The temporal relationship of between objectsover

time

Sequence of operations as a response to one or

more events


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Example of Concurrency within an Object

Emitting

Setting Ready

Up to r eset

Do: Dispense

Cash

Do: EjectCard

Ready

Cash taken

Card taken

Synchronization

Splitting control


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Modeling Concurrency

Two types of concurrency

1. System concurrency

State of overall system as the aggregation of state diagrams,

one for each object. Each state diagram is executingconcurrently with the others.

2. Object concurrency An object can be partitioned into subsets of states (attributes

and links) such that each of them has its own subdiagram. The state of the object consists of a set of states: one state

from each subdiagram.

State diagrams are divided into subdiagrams by dotted lines.


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Vidhya P.M 28

Sate generalization

A nested state diagram is a form of

generalization on states.

Generalization is or-relation.

States may have sub states that inherit

the transitions of their super states just

as classes have subclasses that inherit

the attributes and operations of their

super classes.

S f


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Vidhya P.M 29

Sate of car transmission with

generalization

Transmission

Neutral Reverse

Push R

Push N

Forward

First Second Thirdupshift upshift

downshift downshift

Stop

Push N Push F


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StateGeneralization

Generalization is the or-relationship. The states in the nested diagram are all

refinementsofthestateinthehigh-leveldiagram.

States may have substates that inherit the transitions of their superstates.Anytransitionoractionthatappliestoastateappliestoallitssubstates,unless overridden

byanequivalenttransitiononthesubstate.

Asuperstateisdrawnasalargeroundedboxenclosingallof

itssubstates.Substatesinturncanenclosefurthersubstates.WithinstateForward,substateFirstisthedefaultinitialstate.Forwardisjustanabstractclassstate;controlmust

beinarealstate,suchasFirst.

Neutral Reverse

pushR

Second Third

upshift

downshift

First

downshift

stop

Forward

Transmission

pushN

pushFpushN

Statediagramofcartransmission

withgeneralization

defaultsubstate

upshift

abstractstate

inheritedbyeach

gear

superstate

substate


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Anaggregationandits

concurrentstate

diagrams

Car

Ignition Transmission Brake Accelerator

Starting Onreleasekey

Off[Transmissionin Neutral]

Ignitionturnkeytostart

turnkeyoff


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Neutral Reverse

pushR

Second Third

upshift

First

upshiftstop

Forward

Transmission

pushN

pushFpushN

OnOff

releaseaccelerator

downshift

Accelerator

depressacceleratorOnOff

releasebrake

downshift

Brake

depressbrake


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Vidhya P.M 33

Accelerator

Off On

press

Release

Accelerator

Off

Brake

Off On

press

Release


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Vidhya P.M 34

Functional Modeling


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Vidhya P.M 35

It specifies the results of a computationwithout specifying how or when they arecomputed.

It specifies the meaning of operations inobject model and actions in dynamicmodel as well as constraints in objectmodel.


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DFD

It shows the functional relationships of the

values computed by a system, including input

values, output values and internal data stores.

A DFD is a graph showing the flow of datavalues from their sources in objects through

processes that transform them to their

destinations in other objects.


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Elements of DFD

Processes -> Transform data

Data flow -> move data

Actor ->objects that produce and consumedata.

Data store -> objects that store data

passively.

ProcessName

actorName

Data_storeNameInformation/operation

that modify stored dataInformation received from

stored data


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Data Stores

It is a passive object within the graph thatstores data.

It does not generate any operation but merelyresponds to requests to store and access

data. It is drawn as a pair of parallel lines containing

the name of the store.

Input arrows indicate information or operations

that modify the stored data. Output arrows indicate information retrieved

from data store.

In general data store is implemented as a file.


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Data store for temprature readings..

Readings

Max temp

Min temp


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Vidhya P.M 40

Data store for bank account

Customerwithdraw

-

Account

balance

Double headed arrow indicates that balance is both an i/p and o/p of

Subtract operation.


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Data store for price list for items

Price listItem_name

cost

Find costItem namecost


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A data flow that generates an object

used as the target of another operation is

indicated by a hollow triangle at the end

of data flow.

BankAccountselectaccounts

Customer

name

updaterequest

balance

( i/p and o/p)

Selection with an object as result


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Creation of new object

Create account Bankaccount

AccountCustomer

Name, deposit

account


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Nested DFD

The nesting of a diagram is also called

leveling.

A process can be expanded into another

DFD.


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Control Flows

A data flow diagram shows all possible

computation paths for values.

Decisions and sequencing are control

issues that are part of dynamic model.


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A control flow is a Boolean value that

affects whether a process is evaluated or

not.

It is shown by a dotted line from a

process producing a Boolean value to

the process being controlled.


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Vidhya P.M 47

customer update

verify

Account

password

amount

cash

Coded password

PasswordOK

balance


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Specifying Operations

Each operation may be specified as-

Mathematical functions

Table of input and output values.

Equations

Pre and post conditions

Decisions tables

Pseudo code, etc


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Specification of an operation includes a

signature and a transformation.

Signature defines the interface to the

operation i.e. arguments, value returns.

The transformation defines the effect of

an operation i.e. the output values and

the side effects of the operation on itsoperand objects.


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Operations can be divided into three

parts-

Queries

Actions

Activities


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Query

A query is an operation that has no side

effects on externally visible state of any object.

An action is a transformation that has side

effects on the target object or other objects inthe system reachable from the target object.

Actions can be defined by mathematical

equations, decision trees, decision tables, etc.


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Activity

It is an operation to or by an object that

has duration in time.

It has inherently side effects because of

its extension in time.

Activity only make sense for actors.


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constraints

It shows the relationship between two objects at thesame time (frequency and wavelength )Or betweendifferent values of the same object at different times(no of outstanding shares of mutual fund).

It can appear in each model.

Object constraints specify that some objects dependentirely or partially on other objects.

Dynamic constraints specify relationships among thestates or events of different objects.

Functional constraints specify restrictions onoperations.

A constraint between values of an object over time iscalled as invariant i.e. it specifies that some functionsof values remain constant over time.


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FM Vs OM & DM

FM shows what has to be done by asystem.

The object model shows the doers- the

object. DM shows the sequences in which the

operations are performed.

The three models come together in theimplementation of methods.

FM is a guide to the methods.


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A process is usually implemented as a

method.

Actors and data stores are objects in the

object model.

Data flows are values in object model.


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Relative to functional model the object

model shows the structure of the actors,

data store and flows.

Relative to functional model the dynamicmodel shows the sequence in which

processes are performed.


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Relative to object model the functional

model shows the operations on classes

and the arguments of each operations.

Relative to object model the dynamicmodel shows the states of each object

and the operations that are performed as

it receives events and changes state.


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Relative to dynamic model the functional

model shows the definition of actions

and activities that are undefined with

dynamic model. Relative to dynamic model the object

model shows what changes state and

undergoes operations.

OOMD Module2 Dynamic Modelling

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