A Tool for Choreography Analysis Using Collaboration Diagrams

Tevfik BultanUniversity of California

Santa Barbara

Xiang FuHofstra University

Chris FergusonUniversity of California

Santa Barbara

Outline

• Modeling Service Interactions as Conversations

• Specification of Conversations Using Collaboration Diagrams

• Analyzing Collaboration Diagrams

• Collaboration Diagram Extensions

• Tool Architecture and Experiments

Web Services

The World Wide Web Consortium (W3C) defines a Web service as – "a software system designed to support interoperable machine-to-

machine interaction over a network”

• Web services support basic client/server style interactions

Service Requester

Service Provider

Request

Response

SOAP

WSDL

Client Server

Service Interactions

• One of the main goals of service oriented computing is to facilitate integration and composition of services

• Modeling, specifying and analyzing interactions among services are crucial problems that need to be addressed in order to achieve this goal

• Different service developers that want their services to take part in a composition have to agree on how services will interact with each other

• Web Service-Choreography Description Language (WS-CDL)– WS-CDL specifications describe “peer-to-peer collaborations of Web

Services participants by defining, from a global viewpoint, their common and complementary observable behavior; where ordered message exchanges result in accomplishing a common business goal.”

Web Services Standards Stack

Data

Type

Service Orchestration

Protocol

Web Services Business Process Execution Language (WS-BPEL)

Web Services Description Language (WSDL)

Simple Object Access Protocol (SOAP)

XML Schema (XSD)

Extensible Markup Language (XML)

AtomicService

AtomicService

OrchestratedService

SOAP

WSDL

WSDL

Choreography Web Services Choreography Description Language (WS-CDL)

WS-BPEL

OrchestratedService

WS-BPEL

SOAP

SOAP

SOAP

SOAPWS-CDL

An Example

• Assume four peers (individual services):– Customer, Store, CDSupplier, BookSupplier

• Workflow:– Customer sends an order to the Store– Store checks the availability of the CDs and the books in the order

by sending a cdInquiry message to CDSupplier and a bookInquiry message to BookSupplier

– CDSupplier and BookSupplier send the cdAvailability and bookAvailibility back to the Store

– Store sends orderReply to the Customer

A Model for Composite Web Services

• A composite web service consists of

– a finite set of peers• Customer, Store, CDSupplier, BookSupplier

– and a finite set of messages• Customer Store: order• Store CDSupplier: cdInquiry• Store BookSupplier: bookInquiry• CDSupplier Store: cdAvailability• BookSupplier Store: bookAvailability• Store Customer: orderReply

Asynchronous Communication Model

• We assume that the messages among the peers are exchanged using reliable and asynchronous messaging– FIFO and unbounded message queues

orderCustomer Storeorder

Modeling Interactions as Conversations

• A conversation is the global sequence of messages recorded in the order they are sent [Bultan, Fu, Hull, Su WWW’03]

Conversation

orderCustomer

CDStore

Store

cdInquiryorder

cdInquirycdAvailability

cdAvailability …

Specifying Conversations

• There are lots of allowed conversations for our simple example:

• There are also lots of un-allowed conversations:

cdInqorder cdAvail …bookInqorder bookAvail

bookInqorder cdInq

…

cdInqorder bookInq

……

cdAvailorder cdInq

bookInqorder cdAvail

cdInqbookInq cdAvail

……

…

1:order

:Store

:CDSupplier

:Customer

:BookSupplier

A2,B2/2:orderReply1/A1:cdInquiry

A2:cdAvailability

1/B1:bookInquiry

B2:bookAvailability

Specifying Conversations via Collaboration Diagrams

messagesequencelabel

mustprecede

More On Collaboration Diagramssequencelabel

mustprecede

A2, B2 / 2 : orderReply

message

asynchronouscommunication

synchronouscommunication

cdInquiry [has CD]

conditionalsend

order*iterativesend

1:order

1/A1:cdInquiry

A2:cdAvailability

1/B1:bookInquiry

B2:bookAvailability

A2,B2/2:orderReply

Dependency Among Message Send Events

• Message send events are ordered based on two rules– Implicit: The sequence labels that have the same prefix must be

ordered based on their sequence number– Explicit: The events listed before “/” must precede the current event

initial event

final event

A1:cdInquiry B1:bookInquiry

{1,2,A1,A2,B1,B2}

{2,A1,A2,B1,B2}

1:order

{2,A2,B1,B2} {2,A1,A2,B2}

{2,B1,B2} {2,A1,A2}

A2:cdAvailability

{2,A2,B2}

B1:bookAvailability

{2,B2}

{2}

B2:bookAvailabililty

{2,A2}

2 : orderReply

A1:cdInquiry

A1:cdInquiry

B1:bookInquiry

B2:bookAvailability A2:cdAvailability

A2:cdAvailability B2:bookAvailability

Automata (Conversation Protocol)Construction

1:order

1/A1:cdInquiry

A2:cdAvailability

1/B1:bookInquiry

B2:bookAvailability

A2,B2/2:orderReply

1:order

:Store :CDSupplier

:Customer

:BookSupplier

A2,B2/2:orderReply

1/A1:cdInquiry

A2:cdAvailability

1/B1:bookInquiry

B2:bookAvailability

Store

CDSupplier

?cdInquiry

!cdAvailability

!cdInquiry !bookInquiry

?order

?cdAvailability

!cdInquiry!bookInquiry

?cdAvailability

!bookInquiry

?bookAvailability

?bookAvailability

?bookAvailability

!cdInquiry

?cdAvailability

!orderReply

BookSupplier

?bookInquiry

!bookAvailability

Customer

!order

?orderReply

Implementation with Finite State Machines

Realizability of Collaboration Diagrams

• Not all collaboration diagrams are realizable!

• It is possible to specify interactions that cannot be realized by any peer implementation

• This is a problem!– Assume that we want to specify how several services should interact

with each other– If we write a specification that is not realizable

• the implementation will not be faithful to the specification no matter what we do

:Customer :Store

1:order

:Shipping :Depot

2:ship

Realizability of Collaboration Diagrams

:Customer :Store

1:order

:Shipping :Depot

3:ship

2:orderInfo

RealizableNot Realizable

Realizability of Collaboration Diagrams

RealizableNot Realizable

:Customer :Store

:Accounting

2:bill

1:order

:Customer :Store

:Accounting

3:bill

1:order

2:orderInfo

A Sufficient Condition for Realizability

• We call a send event e well informed – If e is an initial event– Otherwise, let e’ be an immediate predecessor of e

• If e’ is a synchronous send or not conditional or iterative– sender for e should be either the receiver or sender for e’

• If e’ is an asynchronous send and conditional or iterative– sender for e should be the sender for e’ and the receiver for

e should be the receiver for e’ – e should not be conditional or iterative, – e and e’ should not send the same message

• A collaboration diagram is realizable if all its events are well-informed

:Customer :Store

1:order

:Shipping :Depot

2:ship

Realizability of Collaboration Diagrams

:Customer :Store

1:order

:Shipping :Depot

3:ship

2:orderInfo

RealizableNot Realizable

this send eventis not well-informed

Realizability of Collaboration Diagrams

RealizableNot Realizable

:Customer :Store

:Accounting

2:bill

1:order

:Customer :Store

:Accounting

3:bill

1:order

2:orderInfo

this send eventis not well-informed

Collaboration Diagram Extensions

• Collaboration Diagram Sets– The conversation set if the union of the conversation sets of each

collaboration diagram in the collaboration diagram set

• Collaboration Diagram Graphs– Conversation set is obtained by concatenating the conversation sets

of different collaboration diagrams according to the collaboration diagram graph

Collaboration Diagram Sets

• Collaboration diagram sets are more expressive than individual collaboration diagrams

:P :Q

1:x

2:y

:P :Q

2:x

3:y

3:z

1:z

This collaboration diagram set specifies a set of interactions that cannot be specified by any single collaboration diagram

PQ: x

PQ: y

PQ: z

PQ: z

PQ: x

PQ: y

Corresponding conversation protocol

:P :Q1:x

2:y

PQ: x

QP: y

Collaboration Diagram Graphs

• Collaboration diagram graphs are more expressive than collaboration diagram sets

This collaboration diagram graph specifies a set of interactions that cannot be specified by any collaboration diagram set

Corresponding conversation protocol

Analyzing Collaboration Diagram Extensions

• Realizability of collaboration diagram sets and collaboration diagram graphs cannot be determined using the well-informed event rule we discussed earlier

• However, collaboration diagram sets and collaboration diagram graphs can be converted to conversation protocols

• We can use the earlier results on realizability of conversation protocols to determine realizability of collaboration diagram sets and collaboration diagram graphs

RealizabilityAnalyzer

DependencyGraph

Constructor

AutomataConstructor

ConversationProtocol

Translator

CollaborationDiagrams

Realizability Analysiswith WSAT

PromelaTranslator

LTL Model Checkingwith SPIN

PeerSynthesizer

A Tool for Analyzing Collaboration Diagrams

• The tool is implemented as an Add-In to Sparx Systems Enterprise Architect UML Editor

Experiments

Problem Instance Realizability 1 Realizability 2 States

Factory Manager YES NO 383

Order Item NO NO 42 (after fix)

Purchase Order YES NO 246

Company Store YES YES 22

Information Exchange YES YES 50

Voting Booth NO NO 59 (after fix)

Causality Model YES NO 116

orderWindow:OrderEntryWindow

order:Order

macallanLine:OrderLine

deliveryItem:DeliveryItem

macallanStock:StockItem

reorderItem:ReOrderItem

1:prepareOrder

2:prepareOrderLine

3:check

4:remove?

5:needToReorder

6:newReOrder7:newDelivery?

Order Item Example

Conclusions

• Collaboration diagrams are an appropriate specification mechanism for service conversations– There are conditions which guarantee realizability of collaboration

diagrams

• Collaboration diagrams can be generalized to collaboration diagram sets and collaboration diagram graphs– Results on realizability of conversation protocols can be used to

determine realizability of collaboration diagram sets and collaboration diagram graphs

• We implemented these results in a collaboration diagram development tool

THE END

Related Work

• Message Sequence Charts (MSC) – Realizability [Alur, Etassami, Yannakakis ICSE 00, ICALP 01]– Implied scenarios [Uchitel, Kramer, Magee ACM TOSEM 04]

• Modeling agent conversations with Dooley graphs [Parunak, ICMAS 96]

• Conversation protocols [Fu, Bultan, Hull, Su WWW 03] [Fu, Bultan, Su, TCS 04, IEEE TSE 05]

• Modeling services using UML diagrams– [Benatallah, Sheng, Dumas, IEEE IC 03]– [Skogan, Gronmo, Solheim IEEE EDOCC 04]– [Blake ICWS 06]– …

:P :Q

1:x

2:y

:P :Q

:R

3:z

1:y

2:x

An unrealizable Collaboration Diagram Set which consists ofrealizable collaboration diagrams.

:R

:P :Q

1:x

2:y

3:z

An unrealizable Collaboration Diagram Set which consists ofrealizable collaboration diagrams.

:R :P :Q :R

1:y

2:x

:P :Q

1:x

:R :S

2:y

A realizable Collaboration diagram set which consistsof unrealizable collaboration diagrams

:P :Q

2:x

:R :S

1:y