A Tool for Choreography Analysis Using Collaboration Diagrams Tevfik Bultan University of California Santa Barbara Xiang Fu Hofstra University Chris Ferguson University 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) Atomic Service Atomic Service Orchestrated Service SOAP WSDL Choreography Web Services Choreography Description Language (WS-CDL) WS-BPEL Orchestrated Service WS-BPEL SOAP WS-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 order CustomerStore order

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 order Customer CDStore Store cdInquiryorder cdInquirycdAvailability …

Specifying Conversations There are lots of allowed conversations for our simple example: There are also lots of un-allowed conversations: cdInqordercdAvail … bookInqorderbookAvail bookInqordercdInq … orderbookInq … … cdAvailordercdInq bookInqordercdAvail cdInqbookInqcdAvail … … …

1:order :Store :CDSupplier :Customer :BookSupplier A2,B2/2:orderReply 1/A1:cdInquiry A2:cdAvailability 1/B1:bookInquiry B2:bookAvailability Specifying Conversations via Collaboration Diagrams message sequence label must precede

More On Collaboration Diagrams sequence label must precede A2, B2 / 2 : orderReply message asynchronous communication synchronous communication cdInquiry [has CD] conditional send order * iterative send

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 B1:bookInquiry B2:bookAvailability 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 !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 event is 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 event is 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 P  Q: x P  Q: y P  Q: z P  Q: x P  Q: y Corresponding conversation protocol

:P:Q 1:x 2:y P  Q: x Q  P: 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

Realizability Analyzer Dependency Graph Constructor Automata Constructor Conversation Protocol Translator Collaboration Diagrams Realizability Analysis with WSAT Promela Translator LTL Model Checking with SPIN Peer Synthesizer A Tool for Analyzing Collaboration Diagrams The tool is implemented as an Add-In to Sparx Systems Enterprise Architect UML Editor

Experiments Problem InstanceRealizability 1Realizability 2States Factory ManagerYESNO383 Order ItemNO 42 (after fix) Purchase OrderYESNO246 Company StoreYES 22 Information ExchangeYES 50 Voting BoothNO 59 (after fix) Causality ModelYESNO116

orderWindow: OrderEntryWindow order:Order macallanLine: OrderLine deliveryItem: DeliveryItem macallanStock: StockItem reorderItem: ReOrderItem 1:prepareOrder 2:prepareOrderLine 3:check 4:remove? 5:needToReorder 6:newReOrder 7: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

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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 of realizable collaboration diagrams. :R

:P:Q 1:x 2:y 3:z An unrealizable Collaboration Diagram Set which consists of realizable collaboration diagrams. :R:P:Q:R 1:y 2:x

:P:Q 1:x :R:S 2:y A realizable Collaboration diagram set which consists of unrealizable collaboration diagrams :P:Q 2:x :R:S 1:y