WS Orchestration - WSMO

WS Orchestration - WSMO

WS Orchestration Eyal Oren DERI 2004/04/07 Survey of WS orchestration definitions & requirements survey of standards BPEL4WS BPML WSCI survey of vendors Eyal

2 Definitions orchestration this is the private process, our orchestration is subset of this executable process (that interacts with other web services) control from the perspective of one business partner for implementation this is like our choreography workflow choreography

sequence of messages public message exchanges for collaboration protocols Eyal 3 Requirements a-synchronicity we need to have this need message correlation: identifying returning calls exception management

we need to have this services (operations) throw & catch exceptions compensating transactions we need to have this resource locking not feasible reusable composition: separation process logic used web services dont understand, looking goal for capability hierarchy? separation web service capability separation Eyal

4 Standards overview BPEL4WS describes (control logic for) coordination of web services Microsoft, IBM, BEA (XLANG & WSFL) execution environment (BPWS4J) not considered by W3C : not royalty-free BPML describes executable business processes Intalio, Sun, , WSCI describes messages between collaborating web services

Sun, SAP, BEA, Intalio Eyal 5 Standards relation Eyal 6 BPEL4WS (1) (control logic for) coordination of web services abstract processes: choreography public message exchange executable processes: orchestration

private workflow on top of WSDL Eyal 7 BPEL4WS (2) primitive activity (input & input-output operations) invoke

(an operation on a web service) receive (waiting for invocation) reply (responding, in input/output operation) wait (for time) assign (copy & compute data to variables) throw (exception) terminate (stop service instance) empty structure activity (control flow) combines primitives using: sequence, branch, loop, pick, flow need more time to investigate possibilities Eyal 8

BPEL4WS (3) (WSDL defines messages, operations, porttypes) link describes conversation between two roles (specifies porttype of service, to receive messages) multiple messages can be exchanged during conversition we need this too partner: web service with role in linktype (as Axel said on wsmo-d) business process: list of activities (with partners) actual web service grounding can be dynamic unclear yet (WS-Adressing) BPWS4J uses hard-wired at deploy Eyal 9

BPML language for describing business processes simple activity action, assign, call, compensate, delay, fault, synch complex activity all, choice, foreach, sequence, switch, until, while transaction support (compensation, nesting) exception handling (throw, timeout) Eyal 10 WSCI language for describing web services collaboration

message correlation sequencing rules basic: call, delay, empty, fault, spawn, join complex: all, choice, foreach, sequence, is this really only switch, public message exchange then? until, while but cannot specify input/output exception handling transactions Eyal 11 Comparison BPEL4WS BPML+WSCI intentions are the same no comparison in the article, no thorough

search vd Aalst: pattern-based comparison: WSCI BPML offer same functionality too much overlap to justify separation WSCI can be used to model BPEL4WS BPML little more expressive no semantics too many overlapping constructs Eyal 12 Useful for WSMO either: borrow requirements

asynchronicity exception management compensation message correlation control flow construct (workflow patterns, vd Aalst) or: use a standard Eyal 13

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