Activity Diagram - Otto von Guericke University...

Business Informatics GroupInstitute of Software Technology and Interactive Systems Vienna University of TechnologyFavoritenstraße 9-11/188-3, 1040 Vienna, Austriaphone: +43 (1) 58801-18804 (secretary), fax: +43 (1) [email protected], www.big.tuwien.ac.at

Object-Oriented Modeling

Activity Diagram

Slides accompanying UML@ClassroomVersion 1.0

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Literature

The lecture is based on the following book:

Use Case DiagramStructure ModelingState Machine DiagramSequence DiagramActivity Diagram

UML @ Classroom: An Introduction to Object-Oriented ModelingMartina Seidl, Marion Scholz, Christian Huemer and Gerti Kappel

Springer Publishing, 2015

ISBN 3319127411

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Content

IntroductionActivitiesActionsEdges

Control flowObject flow

Initial node, activity final node, flow final nodeAlternative pathsConcurrent pathsObject nodes Event-based actions and call behavior actionsPartitionsException handling

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Introduction

Focus of activity diagram: procedural processing aspectsFlow-oriented language conceptsBased on

languages for defining business processesestablished concepts for describing concurrent communicating processes (token concept as found in petri nets)

Concepts and notation variants cover broad area of applicationsModeling of object-oriented and non-object-oriented systems

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Activity

Specification of user-defined behavior at different levels of granularityExamples:

Definition of the behavior of an operation in the form of individual instructionsModeling the course of actions of a use caseModeling the functions of a business process

An activity is a directed graphNodes: actions and activitiesEdges: for control and object flow

Control flow and object flow define the execution

Optional: ParameterPre- and postconditions

Inputparameter

Node Edge

Outputparameter

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Action

Basic element to specify user-defined behaviorAtomic but can be abortedNo specific rules for the description of an action

Definition in natural language or in any programming languageProcess input values to produce output valuesSpecial notation for predefined types of actions, most importantly

Event-based actionsCall behavior actions

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Connect activities and actions to one anotherExpress the execution order Types

Control flow edgesDefine the order between nodes

Object flow edgesUsed to exchange data or objectsExpress a data/causal dependency between nodes

Guard (condition)Control and object flow only continue if guards in square brackets evaluate to true

Edges

Object flow

Control flow

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Token

Virtual coordination mechanism that describes the execution exactlyNo physical component of the diagramMechanism that grants the execution permission to actions

If an action receives a token, the action can be executedWhen the action has completed, it passes the token to a subsequent action and the execution of this action is triggeredGuards can prevent the passing of a token

Tokens are stored in previous node

Control token and object tokenControl token: “execution permission" for a nodeObject token: transport data + “execution permission”

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Beginning and Termination of Activities

Initial nodeStarts the execution of an activityProvides tokens at all outgoing edgesKeeps tokens until the successive nodes accept themMultiple initial nodes to model concurrency

Activity final nodeEnds all flows of an activityFirst token that reaches the activity final node terminates the entire activity

Concurrent subpaths includedOther control and object tokens are deleted

Exception: object tokens that are already present at the output parameters of the activity

Flow final nodeEnds one execution path of an activityAll other tokens of the activity remain unaffected

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Alternative Paths – Decision Node

To define alternative branches„Switch point“ for tokensOutgoing edges have guards

Syntax: [Boolean expression]Token takes one branchGuards must be mutually exclusivePredefined: [else]

Decision behaviorSpecify behavior that is necessary for the evaluation of the guardsExecution must not have side effects

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Alternative Paths – Merge Node

To bring alternative subpaths togetherPasses token to the next node

Combined decision and merge node

Decision and merge nodes can also be used to model loops:

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Example: Alternative Paths

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Concurrent Paths – Parallelization Node

To split path into concurrent subpathsDuplicates token for all outgoing edges

Example:

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Concurrent Paths – Synchronization Node

To merge concurrent subpathsToken processing

Waits until tokens are present at all incoming edgesMerges all control tokens into one token and passes it onPasses on all object tokens

Combined parallelization and synchronization node:

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Example: Equivalent Control Flowp q

… equivalent to …

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Example: Create and Send Invitations to a Meeting

While invitations are printed, already printed invitations are addressed.When all invitations are addressed, then the invitations are sent.

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Example: Conduct Lecture (Student Perspective)

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NOT equivalent … why?

… the first token that reaches the activity final node terminates the entire activity

… a parallelization node duplicates an incoming token for all outgoing edges

… a decision node passes the token to one outgoing edge (depending on the result of theevaluation of the guard)

… if all incoming edges of an action have a token, the action is activated and is ready for execution

… all outgoing edges of all initial nodes are assigned a token….

… a merge node individually passes each token it gets to its outgoing edge

… a synchronization node waits until all incoming edges have a token, merges them to a singletoken and passes it to its outgoing edge

… before the execution, the action consumes one token from every incoming edge; after the execution, the action passes one token to every outgoing edge

Example: Token (Control Flow)

x x x

x

x

x

xxx x

x

x

xx

x

x

xEnd !

x

x

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Contains object tokensRepresents the exchange of data/objectsIs the source and target of an object flow edgeOptional information: type, state

Notation variant: object node as parameterFor activities

For actions (“pins”)

Object Node

Inputparameter

Outputparameter

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Example: Object Node

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Central Buffer

For saving and passing on object tokensTransient memoryAccepts incoming object tokens from object nodes and passes them on to other object nodesWhen an object token is read from the central buffer, it is deleted from the central buffer and cannot be consumed again

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Data Store

For saving and passing on object tokensPermanent memorySaves object tokens permanently, passes copies to other nodes

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Weight of Edges

Minimal number of tokens that must be present for an action to be executedDefault: 1All tokens present have to be consumed: 0 (also all or *)

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Connector

Used if two consecutive actions are far apart in the diagram

Without connector:

With connector

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Event-Based Actions

To send signalsSend signal action

To accept eventsAccept event action

Accept time event action

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Example: Accept Event Action

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Call Behavior Action

The execution of an action can call an activityContent of the called activity can be modeled elsewhereAdvantages:

Model becomes clearerReusability Name of the called activity

Inverted fork symbol

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Partition

“Swimlane”Graphically or textualAllows the grouping of nodes and edges of an activity due to responsibilitiesResponsibilities reflect organizational units or rolesMakes the diagram more structuredDoes not change the execution semanticsExample: partitions Student and Institute Employee (with subpartitions Professor and Secretary)

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Example: Issue Student ID on Paper (1/2)

State machine diagram of Student ID:

Activity diagram – control flow:

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Example: Issue Student ID on Paper (2/2)

Control flow (green) and object flow (red) in one activity diagram

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Exception Handling – Exception Handler

Predefined exceptionsDefining how the system has to react in a specific error situationThe exception handler replaces the action where the error occurred

If the error e occurs…All tokens in Action A are deletedThe exception handler is activatedThe exception handler is executed instead of Action A

Execution then continues regularly

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Example: Exception Handler

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Exception Handling– Interruptible Activity Region

Defining a group of actions whose execution is to be terminated immediately if a specific event occurs. In that case, some other behavior is executed

If E occurs while B or C are executedException handling is activatedAll control tokens within the dashed rectangle (= within B and C) are deletedD is activated and executed

No “jumping back” to the regular execution!

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Name Notation Description

Action node

Activity node

Represents an action (atomic!)

Represents an activity (can be broken down further)

Initial node Start of the execution of an activity

Activity final node

End of ALL execution paths of anactivity

Notation Elements (1/5)

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Decision node

Merge node

Splitting of one execution pathinto alternative execution paths

Merging of alternative executionpaths into one execution path

Parallelization node

Synchronization node

Splitting of one execution pathinto concurrent execution paths

Merging of concurrent executionpaths into one execution path

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Flow final nodeEnd of ONE execution path of anactivity

Edge Connection between the nodes ofan activity

Call behavioraction

Action A refers to an activity ofthe same name

Partition Grouping of nodes and edgeswithin an activity


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Send signal action

Transmission of a signal to a receiver

Asynchronous accept (timing) event action

Wait for an event E or a timeevent T

Object node Contains data or objects

Parameter for activities

Parameter for actions (pins)

Contains data and objects as inputand output parameters

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ExceptionHandler

Exception handler is executed instead of the action in the event of an error e

Interruptible activity region

Flow continues on a differentpath if event E is detected

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Activity Diagram - Otto von Guericke University...

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