1. ASE2002 -- McIlraith 09/27/2002 Web Services (WS) Web Services are Web-accessible programs and devices. Background

2. ASE2002 -- McIlraith 09/27/2002 Knowledge Rep’n for the “Semantic Web” Background XML Schema RDF (Resource Description Framework) RDFS (RDF Schema) RULE-ML (Logic) DAML+OIL (Ontology) XML (Extensible Markup Language)

3. ASE2002 -- McIlraith 09/27/2002 Broad Objective 1. Self-describing Web Services: automated reasoning techniques that exploits semantic markup to support automated Web service discovery, execution, composition and interoperation. semantic markup to enable automation by making service capabilities, user constraints & procedures computer-interpretable & use-apparent. 2. Automation of Web Service Tasks:

4. ASE2002 -- McIlraith 09/27/2002 Goal Automation of: Web service discovery Find me a shipping service that will transport frozen vegetables from San Francisco to Tuktoyuktuk. Web service invocation Buy me “Harry Potter and the Philosopher’s Stone” at www.amazon.com Web service selection, composition and interoperation Make the travel arrangements for my ASE2002 conference. Web service execution monitoring Has my book been shipped yet? Web service simulation and verification

5. ASE2002 -- McIlraith 09/27/2002 DAML-S: Semantic Markup for Web Services DAML-S: A DARPA Agent Markup Language for Services DAML+OIL ontology for Web services: equivalent to expressive description logic plus (XML) datatypes well-defined semantics decidable ontologies support reuse, mapping, succinct markup,... Developed by a coalition of researchers from Stanford, SRI, CMU, BBN, Nokia, and Yale. (alphabetically: Ankolekar, Burstein, Hobbs, Lassila, Martin, McDermott, McIlraith, Narayanan, Paolucci, Payne, Sycara.) DAML-S version 0.7 posted October,2002 http://www.daml.org/services/ [McIlraith, Son & Zeng, 01] [DAML-S Coalition, 01, 02]

6. ASE2002 -- McIlraith 09/27/2002 DAML-S: An Ontology for Service Description ServiceServiceProfile presents ServiceModel describedBy ProcessModelProcessCtrl Grounding

7. ASE2002 -- McIlraith 09/27/2002 Process Model service process atomic process composite process hasProcess simple process expands collapses control constructs composedBy while sequence If-then-else fork... inputs outputs preconditions effects : function & action metaphor

8. ASE2002 -- McIlraith 09/27/2002 Ontologies of Services Service Shipping BuyBook AmazonBuyBook CongoBuyBook BuyTicket BuyAirTicket Purchase AirShipping TruckShipping BoatShipping AcmeTruckShipping BuyConcertTicket

9. ASE2002 -- McIlraith 09/27/2002 Semantics of DAML-S Problem: DAML+OIL has a well-defined semantics, but it is not sufficiently expressive to characterize all and only the intended interpretations of DAML-S. Solution: 1.Distributed operational semantics defined in terms of Petri Nets.

10. ASE2002 -- McIlraith 09/27/2002 Implications for Decision Procedures Using the Operational Semantics, many service automation tasks can be related to reachability analysis. Expressive Power of DAML-S Reachability Analysis DAML-SP-Space Complete DAML-S w/o Iteration NP Complete DAML-S w/o Iteration, Choice, Condition Polynomial [Narayana & McIlraith, 02]

11. ASE2002 -- McIlraith 09/27/2002 Semantics of DAML-S Problem: DAML+OIL has a well-defined semantics, but it is not sufficiently expressive to characterize all and only the intended interpretations of DAML-S. Solution: 1.Distributed operational semantics defined in terms of Petri Nets. 2. Model-theoretic semantics partially defined by a translation to (mostly) first-order logic.

12. ASE2002 -- McIlraith 09/27/2002 -- i.e., knowledge preconditions -- i.e., (conditional) knowledge effects Recall: atomic and composite services are described in terms of inputs (conditional) outputs preconditions (conditional) effects Composite services have additional encapsulated representations. Modeling Web Services as Actions Web services are encoded as primitive and complex actions Primitive Action/Service: getWeather preconditions: know(cityname(y)) effects: know(weather(y)) Complex Action/Service: buyAirTicket(x)  locateFlight(x);if available(x)  okPrice(x) then provideCustInfo(x); payTicket(x) endif

13. ASE2002 -- McIlraith 09/27/2002 Situation Calculus [Reiter, 01] [McCarthy, 68], etc. We appeal to the “Reiter axiomatization” of the situation calculus. Sorts: Actions e.g., a, bookTaxi(x) Situations e.g., s, S 0, do(bookTaxi(x),s) Fluents e.g., ownTicket(x, do(a,s)) rent-car S0S0 bookAirTicket... bookTaxi bookCruise... bookCar bookHotel do(bookTaxi,S 0 )

14. ASE2002 -- McIlraith 09/27/2002 Situation Calculus [Reiter 01, McCarthy 68], etc. A situation calculus theory D comprises the following axioms: D =   D una  D S0  D ap  D SS domain independent foundational axioms,  unique names assumptions for actions, D una axioms describing the initial situation, D S0 action precondition axioms, D ap, Poss(a,s)   (x,s) e.g., Poss(pickup(x),s)   holding(x,s) successor state axioms, D SS, F(x,s)   (x,s) e.g., holding(x,do(a,s))  a = pickup(x)  (holding(x,s)  (a  putdown(x)  a  drop(x)))

15. ASE2002 -- McIlraith 09/27/2002 Recap 1. Self-describing Web Services: DAML-S: decidable description logic for Web services “side effects” of programs are critical to WS composition semantics defined by translation to (mostly) first-order logic composite services have additional encapsulated representation automating Web service composition  2. Automation of Web Service Tasks:

16. ASE2002 -- McIlraith 09/27/2002 …Composing Semantic-Web Services…

17. ASE2002 -- McIlraith 09/27/2002 Semantic Web Services DAML

18. ASE2002 -- McIlraith 09/27/2002 Automating Web Service Composition Possible Approach: Program Synthesis? Find a computable function body: D  R that satisfies a formal specification Spec=(D,R,I,O). I.e., find body such that O(x,body(x)) holds for all x  D satisfying I(x). What’s different (harder , and easier  )  I/O specification is inadequate – must also consider pgm side effects  specifications are complex constraints based on intermediate state  programs are compositions of component software  search space generally very large  simple sequencing is adequate for many tasks  compositions are generally small Problem: Automatically select and execute services to achieve a user objective. E.g., Make the travel arrangements for my KR2002 conference

19. ASE2002 -- McIlraith 09/27/2002 Automating Web Service Composition Problem: Automatically select and execute services to achieve a user objective. E.g., Make the travel arrangements for my KR2002 conference Approach: I. Plan a sequences of services that realize user’s objective. (NP complete or worse (often P-Space complete))

20. ASE2002 -- McIlraith 09/27/2002 Automating Web Service Composition Problem: Automatically select and execute services to achieve a user objective. E.g., Make the travel arrangements for my KR2002 conference Approach: I. Plan a sequences of services that realize user’s objective. (NP complete or worse (often P-Space complete)) II. Customize reusable generic procedures - Define and archive reusable generic procedures - Customize with user’s constraints. (Same complexity in a reduced search space) Advantages: efficiency, ease of use, customization

21. ASE2002 -- McIlraith 09/27/2002 Generic Procedures Desiderata for Generic Procedures Generic: High degree of non-determinism to accommodate customization. Customizable: Easily customizable by individual users. (Re)Usable: Usable by agents w/ different levels of knowledge  Self-sufficient wrt required knowledge. Interpretable: Able to be interpretted and executed. Claim: Golog is natural formalism for creating generic procedures

22. ASE2002 -- McIlraith 09/27/2002 Golog [Levesque et al. 97, De Giacomo et al. 00, etc] rent-car S0S0 bookAirTicket... bookTaxi bookCruise... bookCar bookHotel procedural constructs: sequence if-then-else nondeterministic choice while-do, etc. Computational Semantics [De Giacomo et al, 00] e.g., Trans(a,s, ,s’)  Poss(a[s],s)   ’ = nil  s’=do(a[s],s) Final(a,s)  false bookTaxi Generic E.g., bookAirTicket(x); if far then bookCar(x) else bookTaxi(y)

23. ASE2002 -- McIlraith 09/27/2002 “Big Do” Do( , s, s’) is an abbreviation. It holds whenever s’ is a terminating situation following the execution of complex action  in s. Each abbreviation is a formula in the situation calculus. Do(a, s, s’)  Poss( a[s],s)  s’= do(  [s],s) Do([a 1 ; a 2 ], s, s’)  (  s*).(Do(a 1, s, s*)  Do(a 2, s*, s’)... E.g., Let  be bookAirTicket(x); if far then bookCar(x) else bookTaxi(y) rent-car S0S0 bookAirTicket... bookTaxi bookCruise... bookCar bookHotel bookTaxi D   s’.Do( , S 0, s’) Generic

24. ASE2002 -- McIlraith 09/27/2002 Customizable: User Customization of Golog E.g., Marielle would like to fly if the driving distance is greater than 3 hours. Marielle must be home for her daughter’s hockey game on April 24. Customizable bookTaxi rent-car S0S0 bookAirTicket... bookTaxi bookCruise... bookCar bookHotel

25. ASE2002 -- McIlraith 09/27/2002 Customizable: User Customization of Golog E.g., Marielle would like to fly if the driving distance is greater than 3 hours. Marielle must be home for her daughter’s hockey game on April 24. Customizable bookTaxi rent-car S0S0 bookAirTicket... bookTaxi bookCruise... bookCar bookHotel New distinguished predicate Desirable(a,s) Modified Computational Semantics Trans(a,s, ,s’)  Poss(a[s],s)    ’ = nil  s’=do(a[s],s) Final(a,s)  false Desirable(a[s],s)

26. ASE2002 -- McIlraith 09/27/2002 Specifying User Constraints Customizable Necessary conditions for a to be desirable in s, D necD Desirable(a,s)   i Desirable(bookAirTicket(o,d,dt,s))  gt(DriveTime(o,d),3,s) Personal Constraints, D PC  (Away(dt,s)  MustbeHome(dt,s)) Assume D necD & D PC specify all conditions under which Desirable(a,s) is true Desirable(a,s)   A   C  D PC  PC

27. ASE2002 -- McIlraith 09/27/2002 Specifying User Constraints Customizable Necessary conditions for a to be desirable in s, D necD Desirable(a,s)   i Desirable(bookAirTicket(o,d,dt,s))  gt(DriveTime(o,d),3,s) Personal Constraints, D PC  (Away(dt,s)  MustbeHome(dt,s)) Assume D necD & D PC specify all conditions under which Desirable(a,s) is true Desirable(a,s)   A   C  D PC  PC  A =  1   2  …   n  bookAirTicket = gt(DriveTime(o,d),3,s)

28. ASE2002 -- McIlraith 09/27/2002 Specifying User Constraints Customizable Necessary conditions for a to be desirable in s, D necD Desirable(a,s)   i Desirable(bookAirTicket(o,d,dt,s))  gt(DriveTime(o,d),3,s) Personal Constraints, D PC  (Away(dt,s)  MustbeHome(dt,s)) Desirable(bookAirTicket(o,d,dt,s))  gt(DriveTime(o,d),3,s)  (d=Home   MustbeHome(dt,s)) Assume D necD & D PC specify all conditions under which Desirable(a,s) is true Desirable(a,s)   A   C  D PC  PC  A =  1   2  …   n  bookAirTicket = gt(DriveTime(o,d),3,s)  PC  R[C(do(A(x)s))]  PC  R [  (Away(dt, do(bookAirTicket(o,d,dt,s)))  MustbeHome(dt, do(bookAirTicket(o,d,dt,s)))]

29. ASE2002 -- McIlraith 09/27/2002 Discussion Desirable individually definable for each user elaboration tolerant (simple rewrite) reduces the search space, rather than providing an evaluation of a sequence of actions after their computation doesn’t account for “soft” constraints (current work) approach amenable to other deontic constraints (e.g., Able, Should) easily implemented in ConGolog interpreter using Trans/Final Customizable

30. ASE2002 -- McIlraith 09/27/2002 Usable: Self-Sufficient Golog Programs Goal: Define Golog programs that are self-sufficient wrt the knowledge they require to execute. Define the notion of self sufficiency of , ssf( ,s), inductively, e.g., ssf(nil, s)  true ssf(a, s)  Kwhether (Poss(a[s], s))  Kwhether (Desirable(a[s],s)) ssf(  1 ;  2, s)  ssf(  1, s)   s’.[Do(  1, s, s’)  ssf(  2, s’)] ssf(if  then  1 else  2, s)  Kwhether (  [s], s)   [s]  ssf (  1, s)]   [s]  ssf (  2, s) etc. Usable

31. ASE2002 -- McIlraith 09/27/2002 Usable: Self-Sufficient Golog Programs Definition [Self-Sufficient Program (KSSF & PSSF)]:  is KSSF relative to theory D and kernel initial state Init  iff D  Init  (S 0 ) and D  ssf ( , S 0 )  true  is physically self-sufficient (PSSF) iff it is KSSF and D  (  s ). Do( ,S 0,s) Usable

32. ASE2002 -- McIlraith 09/27/2002 Interpretable: Middle-Ground ConGolog Interpreter Interpretable

33. ASE2002 -- McIlraith 09/27/2002 Interpretable: Middle-Ground ConGolog Interpreter Trade-off between online interpreter and offline interpreter online: incomplete no backtracking offline: computationally expensive larger search space need to generate conditional plans Interpretable Middle-Ground Interpreter: MG (D, , Init ,  ) Online information gathering interleaved with offline “simulation” of world-altering actions to generate a sequence of actions  w in  for future execution. Benefits of backtracking (offline) + search space reduction (online) Enables user interaction/intervention

34. ASE2002 -- McIlraith 09/27/2002 Why the Interpreter Works Key Idea: Invocation and Reasonable Persistence Assumption (IRP) sensing actions are Poss-ible at the outset (put preconditions in Init  ) fluents affecting decisions ( ?  ), once sensed, persist til final execution Theorem: (“The interpreter does the right thing.”) Given an action theory D and Golog program  such that PSSF( , Init  ) and ( , Init  ) adheres to IRP, suppose MG( D, , Init ,  ) holds for some . Assume that there are no sensor error and that no exogenous actions affect fluents in D, then for all fluents F in D, D  F(x, do(  w, do(  s, S 0 )  F(x, do( , S O )). Interpretable See also [McIlraith & Son, 02] The code that implements the interpreter. How to translate the situation calculus theory to Prolog. Proof of correctness of the implementation.

35. ASE2002 -- McIlraith 09/27/2002 We’ve built it and it’s running on the Web! DAML-enabled web pages Web Service Ontologies Web Procedures Ontologies Agent Broker E-mail DAML-enabled personal/company constraints and prefs... GOLOG

36. ASE2002 -- McIlraith 09/27/2002 Summary 1. Self-describing Web services: DAML-S: decidable description logic ontology for Web services “side effects” of programs are critical to WS composition semantics defined by translation to (mostly) first-order logic 2. Automating Web service composition: Modeled Web Services as primitive and complex actions. Encapsulated representation of complex actions enables automated web service composition via plan-like synthesis. Our approach: Generic Procedures and Customizing User Constraints - Generic- Customizable - Usable- Interpretable Implemented and interpreter proved correct wrt specification. Embedded into a working system that communicates with Web services

37. ASE2002 -- McIlraith 09/27/2002 Related Work Web service descriptions & process models: WSDL, WSFL, XLANG, BPEL4WS, UDDI, BPML, PSL, etc. Internet agents: [Etzioni et al., 94], etc. Program Synthesis: [Bates&Constable, 85], [Burstall&Darlington, 77], [Green, 69], [Manna & Waldinger, 79], [Smith, 94], etc. Golog [Levesque et al., 97], [de Giacomo & Levesque, 99], [Lakemeyer, 99] [Sardina, 01], [Boutilier et al., 01], [Lesperance et al, 01], [Lesperance et al., 02] etc. Web service automation [Waldinger, 00], [Sycara et al. 00], [Denker et al., 01], [McDermott, 02], etc. Ubiquitous Computing [Weiser, 96], etc.

38. ASE2002 -- McIlraith 09/27/2002 Want to Learn More? Papers: http://ksl.stanford.edu/people/sam/publications.html DAML-S: http://www.daml.org/services/ DAML Program: http://www.daml.org/

39. ASE2002 -- McIlraith 09/27/2002 The End