Supporting Adaptive Web-Service Orchestration with an Agent Conversation Framework Warren Blanchet, Eleni Stroulia, Renée Elio University of Alberta

ICWS 2005, Orlando Outline Introduction & Motivation Workflow & Conversations WRABBIT: Workflow reconfiguration Case studies Conclusion & Future work

ICWS 2005, Orlando Web services Pool of available services User doesn’t care about implementation Compose services Use services together to provide higher- level service

ICWS 2005, Orlando Change Web services accommodate change …that doesn’t expose itself at the interface level What about rules on messages exchanged? Compositions: No peers: too centralized Peers: hard to change messages exchanged due to effect on others

ICWS 2005, Orlando Outline Introduction & Motivation Workflow & Conversations WRABBIT: Workflow reconfiguration Case studies Conclusion & Future work

ICWS 2005, Orlando Workflow & Conversations Workflows are processes that produce work products Distribution of abilities requires cooperation Cooperation requires communication Communication requires shared understanding

ICWS 2005, Orlando Conversation model Agent-communication community Agents have a shared conversation model Defines the permissible messages at any point in a conversation Deviation from this model is a conversation error, which will cause the conversation to fail This is signaled by a ‘not-understood’ message Conversation failure indicates the shared model is inconsistent: the parts shared do not match

ICWS 2005, Orlando Web-services Workflow Accomplishing work: web-services Controlling flow between services Equivalent to ‘composition’ BPEL4WS tailored for separation of work and flow for a given workflow participant WS-CDL (forthcoming) means to verify correct information flow between participants

ICWS 2005, Orlando Aside on BPEL-based interaction Suppose a composed service is implemented in BPEL, and has a non-trivial communication protocol How to ensure the service client conforms? Inspect by hand Use a monitoring proxy with an abstract BPEL specification of the client’s communication Merge the client’s abstract BPEL specification of the client’s communication into the client’s executable BPEL specification Use an adapter pattern style executable BPEL client specification Integrate the client’s abstract BPEL specification into the client’s workflow dynamically using constraint- based matching

ICWS 2005, Orlando Observations Each participant in a workflow can be modeled in BPEL4WS Each BPEL file specifies the messages exchanged with its partners The shared workflow model is composed of these per-participant pieces The shared conversation model is a subset of this workflow model

ICWS 2005, Orlando Goal Given: Per-participant workflow model segments (which we call workflow scripts) Conversation failure detection & signaling Produce: A system which can repair inconsistent workflow models (as signaled by conversation failures) automatically

ICWS 2005, Orlando Outline Introduction & Motivation Workflow & Conversations WRABBIT: Workflow reconfiguration Case studies Conclusion & Future work

ICWS 2005, Orlando Introduction WRABBIT: Workflow Reconfiguration with Agent- and BPEL-Based Intercommunication Technology Website:

ICWS 2005, Orlando Requirements WRABBIT agents need: declarative specifications for workflow scripts (BPEL4WS + extra custom stuff) to execute these scripts to recognize conversation failures to determine where to obtain a correct workflow script (if it is at fault) to retrieve the correct workflow script, if necessary to incorporate the new workflow script into its operation

ICWS 2005, Orlando WRABBIT Architecture

ICWS 2005, Orlando WRABBIT Details: Messaging WRABBIT agents use an ACL for a message transport layer This allows agents to send out-of-band information such as conversation failure signals (not-understood) A straightforward mapping from WSDL operation types to mini-protocols one-way: (inform) request-response: (inform)(request)

ICWS 2005, Orlando WRABBIT Details: Workflow Script Execution WRABBIT agents may be configured: to execute particular scripts in response to incoming messages to execute a script that satisfies some criteria Workflow scripts inherit BPEL features importantly can be executable or abstract

ICWS 2005, Orlando WRABBIT Details: Workflow Script Composition Why leave scripts abstract? Loose coupling Easy updating WRABBIT agents compose abstract scripts automatically through means-end analysis Others have done this more thoroughly, this work uses a very simplistic method, and assumes a better mechanism exists

ICWS 2005, Orlando WRABBIT Details: Conversation Failure Detection WRABBIT agents use the BPEL-derived workflow scripts to detect conversation failure Failure categories: Invalid content: message payload unfamiliar Invalid sender: the model does not allow this sender for this message Message unexpected: the message is not valid in the current context

ICWS 2005, Orlando WRABBIT Details: Conversation Failure Recovery WRABBIT agents first determine who is the authority for a given failure May depend on failure type, workflow script, etc. WRABBIT agents rely on a shared policy to determine the authority Then, agents exchange the files that define the authoritative workflow script

ICWS 2005, Orlando Outline Introduction & Motivation Workflow & Conversations WRABBIT: Workflow reconfiguration Case studies Conclusion & Future work

ICWS 2005, Orlando Environment Academic department Agents: Instructor Department administration employee Story: the Department agent dispenses student transcripts the Instructor agent uses this service

ICWS 2005, Orlando Missing Precondition Study Change: To get a student transcript, you now have to provide an authorization token A separate service of the Department agent provides these tokens The token is provided in a new message at the beginning of the agents’ interaction

ICWS 2005, Orlando Missing Precondition Study (2) The Department agent is updated The Instructor agent has not The Instructor agent begins the conversation with the first message (from its perspective) which is the second message from the Department agent’s view Not-understood!

ICWS 2005, Orlando Missing Precondition Study (3) The Department agent is the authority, so it does nothing The Instructor gets the new script from the Department agent The Instructor then retries It discovers it needs to satisfy the new abstractness It does so with the authorization workflow, and successfully obtains its transcript

ICWS 2005, Orlando Missing Precondition Study Trace

ICWS 2005, Orlando Outline Introduction & Motivation Workflow & Conversations WRABBIT: Workflow reconfiguration Case studies Conclusion & Future work

ICWS 2005, Orlando Summary WRABBIT is an agent-based (peer-to-peer, distributed) framework executes BPEL4WS web-service compositions identifies and dynamically recovers from conversation failures has been tested with case studies

ICWS 2005, Orlando Contributions WRABBIT enables flexibility Service owners can change their services without an involved migration process Service ownership can be distributed without anarchy

ICWS 2005, Orlando Future work Better support for new script preconditions Rollback/compensation Negotiation policies

ICWS 2005, Orlando Questions? IT