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Automatic Composition of Transition-based Semantic Web Services with Messaging Daniela Berardi, Diego Calvanese, Guiseppe De Giacomo, Richard Hull, and.

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Presentation on theme: "Automatic Composition of Transition-based Semantic Web Services with Messaging Daniela Berardi, Diego Calvanese, Guiseppe De Giacomo, Richard Hull, and."— Presentation transcript:

1 Automatic Composition of Transition-based Semantic Web Services with Messaging Daniela Berardi, Diego Calvanese, Guiseppe De Giacomo, Richard Hull, and Massimo Mecella September 2, 2005 Affiliations: Berardi, De Giacomo, Mecella: Università di Roma La Sapienza Calvanese: Libera Università di Bolzano/Bozen Hull: Bell Labs Research, Lucent Technologies

2 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB The Web: Yesterday, today, tomorrow 10 years ago HTML, Web browsers established Amazon.com launched Web access only by landline Today Trillions of content-based web pages Thousands of human-machine e-commerce/e-service sites, some offering programmatic interfaces Keyword-based search for web sites Broadband wireless access to laptops; web on cell phones 10 years from now Proliferation of converged services; always-on connectivity 100Ks or Ms of machine-machine e-commerce/e-service sites The semantic web: search based on web contents/services

3 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Automation of: Web service discovery Find me a shipping service that will transport fresh seafood from Trondheim to Paris. Web service invocation Obtain 100 kilos of Norwegian herring for Paris Fish Market Web service selection, composition and interoperation Establish on-going shipments of Norwegian herring. Web service execution monitoring Has the herring shipment been delayed this week? Web service simulation, verification, exception handling Working with web services 10 years from now Broad application in retail e-commerce, supply chain, e-government, communications, entertainment/gaming

4 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Key Building Blocks for this Vision Reasoning about message passing –Cf. Conversation model [Bultan et al, WWW 03], etc. –FSM internal model for receive/send messages –Relating local/global messaging behavior Reasoning about semantics, i.e., impact on the world –Cf. OWL-S [OWL-S Coalition, 03], etc. –Composition results typically focus on single-use Reasoning about the internal processes of web services –Cf. Roman model [Berardi et al, ICSOC 03], etc. –Alphabet of abstract actions –FSM internal model –Results construct re-usable compositions Early foundations work focuses on building blocks individually It is now time to use a single, unified model

5 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB SOAP WS- Choreography SIP Web Services Standards Stack: Key Elements Network Payload Messaging (Individual) Service Description Composition Choreography Discovery HTTP, SMTP, FTP, etc. UDDI OWL-S ServiceProfile WSCL WSDL BPEL4WS OWL-S ServiceModel Focus of talk: a web service model inspired by aspects of these standards 3GPP IMS

6 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Outline Background Colombo: A formal model that combines the key building blocks for semantic web services Automated synthesis of mediators and choreographies in Colombo Related work and conclusions

7 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Store Ware- House Bank Impact on real world Colombo: Combining the key building blocks, while respecting existing standards, approaches Real World Client (human or machine) View of internal process model – modeled as relations or FOL Messages between services – automata based

8 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Colombo: A general model, with specialization to achieve first results The general model incorporates –Impact on real world: cf. OWL-S atomic process Incorporate explicit database manipulations –Message passing: cf. WSDL and other standards –Process model inside web service: FSM-based As in Roman, Conversation, Guarded Automata models –System: Collection of interoperating services For our first results (this paper) –Willing to impose many restrictions Key-based relations, limitations on recursion, … –Hopefully, can generalize the results in subsequent research

9 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB World, Access Functions, Accessible Terms Restriction World relations have keys (can be k-ary) Access functions, e.g., f 2 Inventory (HP15) = NGW Accessible terms over constants C, variables V: Elements of C or V; f j R ( 1,…, m ) for accessible terms j Restriction All database access is via key-based look-up, using accessible terms HP15TNGW5 HS72FSW10... Inventory code availablewarehouseprice 22Romenot committed16 July... Shipment order# address status delivery date

10 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Atomic Process Atomic process is stateless –World relations provide some state Execution is atomic in transactional sense checkItem: I: item:Dom = ; O: avail:Bool; wh:Dom = ; price:Dom ; Effects: if f 1 Inventory (item) = T then avail:= T and wh := f 2 Inventory (item) and p := f 3 Inventory (item) and either no-op on Inventory or modify Inventory(item;F, -, -) if f 1 Inventory (c) = F then avail:= F (Typed) input arguments (Typed) output arguments Conditional effects Effect expressed in terms of Impact on output arguments Insert, delete, modify on world relations (These express full set of effects) Effects can be non-deterministic on world relations Reflects possibility that the abstract model of the world is incomplete

11 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Advertised behavior of web service as guarded automaton Local store Edge conditions based on local store (and incoming message) Edge actions –Atomic Process –Create/send message –Read message Restriction Queue length: 1 Blocking reads ?requestOrder( payBy,cartNum, addr,price) (payBy == PREPAID) (price 10) / charge(cartNum; paymentOK) (payBy == CC) (price > 10) / ! requestCCCheck(cartNum) ?replyCCCheck( approved) ? requestShipStatus(oid) ! shipStatus( oid,date,status) checkShipStatus( oid; date,status) paymentOK == T / requestShip(wh,addr; oid,date,status) approved == F / ! replyOrder(fail) paymentOK == F / ! replyOrder(fail) ! shipStatus( oid,date,status) approved == T / requestShip( wh,addr; oid,date,status)

12 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Web Services System More Restrictions No External Access: for now, no other systems impact world Blocking behavior: Services block when waiting for a read S = ( C, F = {S 1, …,S n }, L ) Client – sends/receives messages; Largely non-deterministic Services Linkage: specifies channels between services (and client) C S1S1 S3S3 S2S2 The Si s impact real world via embedded atomic processes

13 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Each edge satisfies, and labeled by trace, which records ground message sent/received or atomic process invoked Execution Trees and Equivalence Essence of an execution tree: Project onto –Atomic process invocations –Messages from/to client Intuitively: the observables to client, external world Equivalence of two systems: –If essences of execution trees are isomorphic... Each node labeled (id, I ) S = ( C, F = {S 1, …,S n }, L )

14 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Outline Background Colombo: A formal model that combines the key building blocks for semantic web services Automated synthesis of mediators and choreographies in Colombo Related work and conclusions

15 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB ? ? ? S 14 S8S8 S2S2 Mediator-centric Composition Select from UDDI, construct mediator and linkage Interaction with C, and with real world, should copy G C C G S1S1 S2S2 S3S3... UDDI M

16 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Composition Synthesis Result Goal system: S = ( C, G = {G}, L ) – Goal G has atomic processes and messages to C Problem: Given Goal system and UDDI directory, –Select {S 1, …,S n } from UDDI –Build mediator M –Build linkage L so that ( C, S = {M, S 1, …,S n }, L ) is equivalent to the goal system Thm: Can determine existence of (and build) a (p,q)-bounded mediator in doubly exptime –Restrict to fully mediated systems: Client communicates only with mediator; mediator has no atomic processes –(p,q)-bounded: M has at most p states, q variables

17 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB ? ? ? S 14 S8S8 S2S2 Choreography Synthesis Select from UDDI, and construct a linkage Again, interaction with C and real world should copy G C C G S1S1 S2S2 S3S3... UDDI

18 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Choreography Synthesis Result Goal system: S = ( C, G = {G}, L ) – Goal G has atomic processes and messages to C Problem: Given Goal system and UDDI directory, –Select {S 1, …,S n } from UDDI –Build linkage L so that ( C, S = {S 1, …,S n }, L ) is equivalent to the goal system (no mediator) Thm: Can determine existence of (and build) a choreography in doubly exptime –Variant of previous proof, in which mediator is severely restricted (so (p,q)-bounded is implicit)

19 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Proof highlights (1): Infinite to Finite Working with data –Data domains are unbounded size –Execution trees have unbounded branching How do we turn this into a finitely branching system? –Use symbolic values instead of concrete values –Rely on key-based look-ups –Symbolic values may be related in different ways Focus on Symbolic Value Characterization (svc) Work with complete boolean formula about relationships of all symbolic variables to each other, and to constants –Accessible terms Act kind of like Skolem terms, but distinct terms may evaluate to same concrete value Lemma: There is natural homomorphism from concrete exec trees to symbolic exec trees

20 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Proof highlights (2): Embedding symbolic world into PDL Generalization of approach taken by Roman composition synthesis results [Berardi et al, ICSOC 03] –Propositions for each state of each UDDI service, Goal service, relationships between symbolic values –Sentences for new symbolic values coming from DB reads –Sentences that address FSM properties –Sentences for Mediator/Linkage vis-à-vis Goal service Generalizations needed –Working with (symbolic) model of world instance –Non-determinism from possible values in world instance –Non-determinism from non-deterministic conditional effects –In Roman results, things are more synchronized (We need to analyze our embedding more carefully – may obtain tighter complexity bounds)

21 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Outline Background Colombo: A formal model that combines the key building blocks for semantic web services Automated synthesis of mediators and choreographies in Colombo Related work and conclusions

22 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Selected related work ASTRO: Composition with planning via symbolic modeling [Pistore et al, ISWC 04, ICWS 05] –Service models are inspired by OWL-S, BPEL –Uses MBP planner to build mediator satisfying the CTL-based goal First-order Logic Ontology for Web Services (FLOWS) [http://www.daml.org/services/swsf/1.0/overview/] –An extension of PSL – a first-order situation calculus –Impact on world, messages as first-class citizens –Agnostic on process model – can model flowcharts, Golog, FSMs, … Web Services Modeling Ontology (WSMO) [www.wsmo.org] –An ontology for web services –Follows OWL-S notion of service profile (input, output, condition, effect) –Uses Abstract State Machines as basic model for service descriptions [Deutsch et al, PODS 04] –Verification for single web service –Based on Abstract State Machines, with impact on relational database Meteor-S framework (also WSDL-S) [Sheth et al 03, 04, 05] –Position WSDL input/output types in domain ontologies –Composition by selecting atomic processes and placing into stylized workflow template See also recent Hull-Su survey in SIGMOD Record, June, 2005

23 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Conclusions Semantic Web Services should combine: –Semantic atomic processes that change the world –Messages for communication between web services –Ability to describe process model inside web services Colombo –Targeted model for Semantic Web Services, with guarded automata as internal process model –Mediator and Choreography synthesis, against a UDDI populated with richly described services Many restrictions in order to achieve first family of results –Emphasis on re-usable composition, rather than use-once Some next steps –Optimize our reduction, e.g., remove some restrictions, get to EXPTIME –Relax notion of goal, e.g., along lines of ASTRO –Develop a theory of queries over Colombo (or FLOWS) services, to support web services discovery

24 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Backup Slides

25 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Colombo Model: Overview Real world modeled by keyed relations Atomic Processes modeled after OWL-S –Atomic Process can read/write selected world relations Web Service: Guarded automaton –Local store (with scalars) –Transitions have conditions based on local store –Transitions have actions: Atomic Process Send message Receive message –Ports (reminiscent of WSDL) System: family of web services, with linkage –Instantaneous description, (id, I ) (id, I ) –Execution tree Focus on –Systems with a client –Web services drawn from pre-existing set (UDDI directory)

26 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Mapping symbolic world into Propositional Dynamic Logic Propositional Dynamic Logic (PDL) –Well-known modal logic for reasoning about programs –[e.g., short intro in The Description Logic Handbook] Formulas: built from propositional letters (or fluents ) Programs: built from atomic Programs == f | | | [r] | r f is true in current state starting from current state, every execution of r leads to state in which is true starting from current state, some execution of r leads to state in which is true r == P | r r | r;r | r* ( | ? | r – )

27 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Semantics for PDL Models have the form (a Kripke structure) M = ( S, { R P }, ) Set of states For each atomic program P, a binary relation over S – transition relation : S 2 {fluents} (for each state s, which fluents are true in s) M, s f if f(s) M, s if M, s and M, s... R P S x S for each atomic program P R r;r = R r R r... | = | = | = | =

28 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Key results for PDL M satisfies if for some state s, M, s is valid in M if for each state s, M, s if is valid in every M that satisfies | = | = | = Thm: –Satisfiability is ExpTime complete – is satisfiable iff there is a model with size at most exponential in | | (and this can be constructed in exponential time) Tree model property: each model can be unwound to form a model that has a tree structure

29 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Composition with Planning via Symbolic Modeling [Pistore, Traverso et. al.] Approach taken Start with a targeted model of available services –[ISWC 04] Start with OWL-S services Models conditions about state of world but not impact on the world –[ICWS 05] Start with BPEL services Specify desired goal in terms of EaGle –Variant of CTL, incorporates preferences, handling of failure of subgoals Attempts to build a mediator to satisfy goal Applies a Planning as Model Checking tool –Various restrictions, e.g., synchronous messages, bounded ranges, End-to-end implementation, using MBP planner Comparison to Colombo synthesis results Focus on theoretical result, with absolute answers Combines OWL-S + automata-based process model Impact on world modeled explicitly –Key-based access restriction

30 September 1, 2005 Automatic Composition of Semantic Web Services, VLDB Selected References R. Hull and J. Su, Tools for Composite Web Services: A Short Overview, ACM SIGMOD Record, Volume 34, Number 2, June (Many references are available here.) R. Hull, Web Services Composition: A Story of Models, Automata and Logics, keynote at Intl. Conf. on Web Services (ICWS), June 2005, Orlando, Fl, available at services-at-ICWS.ppt D. Berardi, D. Calvanese, G. De Giacomo, R. Hull, M. Marcella, Automatic Composition of Transition-based Semantic Web Services with Messaging, VLDB 2005 (focus of this talk), available at berardi.pdf. Appendix available as Tech. Report , Universita di Roma La Sapienza, Semantic Web Services Framework: In particular, in version 1.0 the document The Semantic Web Services Ontology (SWSO). (This is a draft document and will evolve.) OWL-S: and in particular version 1.1 (dated 11/2004) and the OWL-S white paper s/1.1/overview The ASTRO project at the University of Trente, Italy, including P. Traverso, M. Pistore and others: The Meteor-S project at University of Georgia, including A. Sheth and others, including pointers to WSDL-S activities: A. Deutsch, L. Sui, and V. Vianu. Specification and verification of data-driven web services. In Proc. ACM Symp. on Principles of Database Systems, 2004.


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