Automatic Composition of e-services: The Roman way. Daniela Berardi Dipartimento di Informatica e Sistemistica Università di Roma La Sapienza

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1 Automatic Composition of e-sevices: The Roman way Daniela Beadi Dipatimento di Infomatica e Sistemistica Univesità di Roma La Sapienza beadi@dis.unioma1.it

2 Daniela Beadi Oveview Activity based model: the Roman appoach Composition esults in the Roman model Message based model Activity vs Message based model Embedding Activity based model into SitCalc Embedding Activity based model into PSL

3 Daniela Beadi e-sevices and Community of e-sevices: The Model used by Roman Results An e-sevice is an inteactive pogam that expots its behavio in tems of an abstact desciption A client selects and inteacts with it accoding to the desciption expoted A community of e-sevices is: a set of e-sevices that shae implicitly a common undestanding on a common set of actions and expot thei behavio using this common set of actions A client specifies needs as e-sevice behavio using the common set of actions of the community

4 e-sevice Expots its Behavio Many possible ways. In this talk Behavio modeled by finite state machines coe of state chat, UML state-tansition diagam, etc. in ou FSMs, each tansaction coesponds to an action (e.g., seach-by autho-and-select, seach-by title-and-select, listenthe-selected-song, ) In fact using a FSM we compactly descibe all possible sequences of deteministic (atomic) actions: tee of all possible sequences of actions Datapoduced by actions not explicitly modeled data ae used by the client to choose next action Daniela Beadi

5 Daniela Beadi e-sevice as Execution Tee Requied behavio epesented as a FSM Execution tee (obtained by FSM unfolding) a S 0 a b S 0 b a b a b a: seach by autho (and select) b: seach by title (and select) : listen (the selected song)

6 e-sevice Composition in the Roman Famewok Given: Community C of e-sevices (expessed as FSMs) ) Taget e-sevice S 0 (again expessed as FSM) S 1 S 0 a b a S 2 b Find: new FSM e-sevice S S (delegato): - new alphabet = actions x (sets of sevice identifies) - accepts same language as S 0 - Fo each accepting un of S on wod w, and fo each S in C, pojection of this un onto moves of S is an accepting computation fo S Daniela Beadi,1 S a,1 b,2,2

7 Daniela Beadi Key Idea fo Finding Composition: Exploit Desciption Logics (DLs) Desciption Logics: epesent knowledge in tems of classes and elationships between classes equipped with decidable easoning Inteesting popeties: Tee model popety Small model popety EXPTIME decidability

8 Daniela Beadi Results on Automatically Building e-sevice Composition DL encoding of taget e-sevice DL Knowledge Base: e-sevice composition DL encoding of i-th component e-sevice DL additional domain- independent conditions 0 i aux Init Check satisfiability (and build a model),1,2 a,1 b,2 Initially all e- Sevices ae in thei initial states EXPTIME

9 Daniela Beadi Results Thm 1: Composition exists iff DL Knowledge Base satisfiable Fom composition labeling of the taget e-sevice one can build a tee model fo the Knowledge Base, and vice-vesa Co 1: Composition existence of e-sevices, expessible as FSMs, is decidable in EXPTIME Thm 2: If composition exists then finite state composition exists. Fom a small model of a DL Knowledge Base, one can build a finite state composition Co 2: Finite state composition existence of e-sevices, expessible as FSMs, is decidable in EXPTIME Building finite state composition can be done in EXPTIME

10 Daniela Beadi Message Based Model ec-schema: finite set of abstact pees (e-sevices) pees can be implemented as FSM with input/output each pee has a (bounded) queue asynchonous communication between pees finite set of channels i.e., {<sende, eceive, message_type>} finite set of incoming and outgoing messages ove some alphabet Σ input messages:?a, a Σ output messages!a, a Σ As technical simplification in theoetical model, each symbol a encodes a tiple <sende,eceive,message-type> Convesation language: sequence of messages exchanged between pees Model is pee-to-pee, but can estict to mediated by assuming hub-and-spoke connection gaph. (I.e., one pee acts as the mediato)

11 Daniela Beadi E-Composition Schema An E-C schema specifies the infastuctue of composition Assume finite domains can model paametes stoe ode 1 eceipt 1 eceipt 2 ode 2 authoize ok payment 1 bill 1 bill 2 payment 2 bank supplie1 supplie2

12 Composition Infastuctue Pee-to-pee (distibuted contol) authoize stoe ok ode 1 eceipt 1 ode 2 eceipt 2 payment 1 bill 1 payment 2 bank bill 2 supplie1 supplie2 stoe a o k mediato a k b p bank o 1 b 2 p 2 1 b 1 p1 2 supplie1 o 2 supplie2 Hub-and-spoke (centalized contol) Daniela Beadi

13 Daniela Beadi Pee Synthesis Statement and Results Poblem statement Given: ec-schema and LTL fomula ϕ Ceate: a FSM fo each pee so that ϕ is satisfied Note: not a composition poblem, because this esult is ceating pees, not selecting them fom a pe-existing UDDI Synthesis esults fo Mealy implementations with bounded queues Mealy pee synthesis: decidable Popositional LTL desciption PSPACE (Also, esults contasting bounded vs. unbounded message queues)

14 Daniela Beadi Roman Activity Based Composition Result vs Message Based Synthesis Result Activity based Model: behavio modeled as FSM, with tansitions labeled by actions client/seve model: active client: s/he selects fom a set of choices pesented by e-sevice Result Stat with community of activitybased FSMs (e-sevices) FMSs define constaint on legal sequence of actions executed by each pee given a banching time spec. Ψ of global behavio and constained pees, synthesize a delegato pees communicate only with delegato deteminism only (fo the moment) Message based Model: behavio modeled as FSM, with tansitions labeled by input/output messages pee-to-pee model; no notion coesponding to client in activity model Result Stat with ec-schema which establishes topology fo message-passing no constaint on legal sequences of actions executed by each abstact pee given a LTL spec.φ of global behavio and ec-schema, synthesize pees such that Φ is ealized pee-to-pee communication non deteminism ove messages (i.e., same message labeling diffeent tansition fom same state)

15 Daniela Beadi Roman Activity Based vs Message Based Roman Activity based and Message based ae complementay appoaches: Can mege them? How? (othe) Roman Activity based futue wok: is ou algoithm EXPTIME-had? cuently we ae woking on a DL based pototype system that implements ou composition algoithm also woking on notion of k-look-ahead compositions - gives moe flexibility than fist Roman esults add non deteminism data (i.e., paametes of actions)

16 Daniela Beadi Situation Calculus Encoding of Roman Model -- Idea Each e-sevice i as Reite s Basic Action Theoy Γ i : each action as a Situation Calculus action each state of FSM is a fluent special fluent Final to indicate situation when e-sevice execution can stop. In Γ i we have complete infomation on the initial situation and hence on the whole theoy. e-sevice composition: epesent which e-sevices (in the community) ae executed, when an action of the taget e-sevice is pefomed, by pedicates Step i (a, s), denoting that e-sevice i executes action a in situation s. Situation Calculus Theoy (but not basic) Incomplete infomation ove Step i (a, s) ename Poss to Poss i, ename Final to Final i suitably modify the successo axioms to cope with Step i (a, s)

17 Daniela Beadi Sit Calc Encoding -- Details Taget e-sevice E 0 = (Σ, Q 0, q 0 0, δ 0, F 0 ) (Reite Basic Action Theoy) F q00 (S 0 ) initial situation s. F q (s) F q (s) fo all pais of distinct states q, q in E 0 e-sevice states ae pai-wise disjoint s. Poss(a, s) q st δ0(q, a) is defined F q (s) s α. F q (do(α,s)) a, q, st q =δ0(q, a) (α = a F q (s)) (F q (s) b st δ0(q',b) is defined α b) fo each q'=δ 0 (q,a) taget e-sevice can do an a-tansition going to state q s. Final (s) q F0 F q (s) denotes taget e-sevice final states

18 Sit Calc Encoding -- Details (cont.d) Community e-sevices E i = (Σ, Q i, q 0 i, δ i, F i ) F qi 0 (S 0 i ) initial situation s. F q (s) F q (s) fo all pais of distinct states q, q in E i e-sevice states ae pai-wise disjoint s. Poss i (a, s) q st δi(q, a) is defined F q (s) s α. F q (do(α,s)) ( a, q, st q =δi(q, a) (α = a F q (s) Step i (α, s))) ( Step i (α, s) F q (s)) Daniela Beadi fo each q =δ i (q, a) if e-sevice moved then new state, othewise old state s. Final i (s) q F i F q (s) denotes community e-sevice final states

19 Daniela Beadi SitCalc Encoding -- Details (cont.d) Foundational, domain independent axioms: s,a. Poss(a,s) Final(s) i=1..n Step i (a,s) Poss i (a,s) fo each action a at least one of the community e-sevices must move at each step s. Final(s) i=1..n Final i (s) when taget e-sevice is final all comm. e-sevices ae final i=0..n F qi 0 (S 0 i ) in the initial situation all e-sevices ae in thei initial state

20 Daniela Beadi PSL Encoding of Roman Model -- Idea Based on Rick Hull and Michael Guninge encoding of message based model in PSL Basic idea to model an e-sevice: fluents to denote: initial situation (Init) states of FSM (F q ), final states (Final), one activity fo each action. Component e-sevices: ename poss to poss i, ename Final to Final i fluent Step ai to denote which component e-sevice moves

21 Daniela Beadi PSL Encoding of Roman Model -- Idea Based on Rick Hull and Michael Guninge encoding of message based model in PSL Basic idea to model an e-sevice: fluents to denote: initial situation (Init) states of FSM (F q ), final states (Final), vey simila to Sit Calc! one activity fo each action. Component e-sevices: ename poss to poss i, ename Final to Final i fluent Step ai to denote which component e-sevice moves

22 Daniela Beadi PSL Encoding -- Details Taget e-sevice E 0 = (Σ, Q 0, q 0 0, δ 0, F 0 ) o.pio (F q F q, o) fo all pais of distinct states q, q in E 0 e-sevice states ae pai-wise disjoint o. holds(f q,o) poss(a, o) (pec) o. occuence_of(o,a) pio(f q, o) holds(f q, o) (eff) fo each q'=δ 0 (q,a) taget e-sevice can do an a-tansition going to state q o. holds(f q,o) poss(a, o) false fo each δ 0 (q,a) undef. taget e-sevice cannot do an a-tansition Final q F0 F q denotes taget e-sevice final states

23 Daniela Beadi PSL Encoding -- Details Taget e-sevice E 0 = (Σ, Q 0, q 0 0, δ 0, F 0 ) o.pio (F q F q, o) o. holds(f q,o) poss(a, o) (pec) o. occuence_of(o,a) pio(f q, o) holds(f q, o) (eff) o. holds(f q,o) poss(a, o) false Final q F0 F q simila to Sit Calc!

24 Daniela Beadi PSL Encoding -- Details (cont.d) Community e-sevices E i = (Σ, Q i, q 0 i, δ i, F i ) o.pio (F q F q, o) fo all pais of distinct states q, q in E i e-sevice states ae pai-wise disjoint o. holds(f q,o) poss i (a, o) (pec) o. occuence_of(o,a) pio(f q, o) (eff) (holds(f q, o) holds(step ia, o)) (holds(f q, o) holds(step ia,o)) fo each q'=δ i (q, a) if e-sevice moved then new state, othewise old state o. holds(f q,o) poss i (a, o) false o. occuence_of(o, a) pio(f q, o) holds(f q,o) holds(step ia, o) fo each δ i (q,a) undef. if e-sevice cannot do a, and a is pefomed then it did not move Final i q Fi F q denotes community e-sevice final states

25 Daniela Beadi PSL Encoding -- Details (cont.d) Community e-sevices E i = (Σ, Q i, q 0 i, δ i, F i ) o.pio (F q F q, o) o. holds(f q,o) poss i (a, o) (pec) o. occuence_of(o,a) pio(f q, o) (eff) (holds(f q, o) holds(step ia, o)) (holds(f q, o) holds(step ia,o)) o. holds(f q,o) poss i (a, o) false o. occuence_of(o, a) pio(f q, o) holds(f q, o) holds(step ia, o) Final i q Fi F q simila to Sit Calc!

26 Daniela Beadi PSL Encoding -- Details (cont.d) Additional assetions: o. poss(a, o) occuence_of(o,a) i=1..n step ia (o) poss i (a,o) fo each action a at least one of the community e-sevices must move at each step o. pio (Final i=1..n Final i, o) when taget e-sevice is final all comm. e-sevices ae final Init i=0..n F qi0 Initially all e-sevices ae in thei initial state

27 Daniela Beadi PSL Encoding -- Details (cont.d) Additional assetions: o. poss(a, o) occuence_of(o,a) i=1..n step ia (o) poss i (a,o) o. pio (Final i=1..n Final i, o) Init i=0..n F qi0 simila to SIt Calc!

28 Daniela Beadi Info & Contacts Thesis dissetation scheduled fo Januay 2005 Daniela Beadi home page: addess: Via Salaia, 113 (2 piano) I Rome (Italy)

29 Back up

30 Daniela Beadi An execution tee 0 a b a b a b Execution tee a: seach by autho (and select) b: seach by title (and select) : listen (the selected song) Nodes: histoy (sequence) of actions executed so fa Root: no action yet pefomed Successo node x a of x: action a can be executed afte the sequence of action x Final nodes: the e-sevice can teminate

31 Daniela Beadi e-sevice composition Added value of the community: when a client equest cannot be satisfied by any available e- Sevice, it may still be possible to satisfy it by combining pieces of e-sevices in the community Two issues aise: suppot fo synthesizing composition: automatic synthesis of a coodinating pogam (composition) that ealizes the taget e-sevice (client equest) by suitably coodinating available e-sevices addessed hee suppot fo ochestation: execution of the coodinating pogam not addessed hee

32 Daniela Beadi Fomalizing e-sevice composition Composition: coodinating pogam that ealizes the taget e-sevice by suitably coodinating available e-sevices Composition can be fomalized as: a labeling of the execution tee of the taget e-sevice such that each action in the execution tee is labeled by the community e-sevice that executes it and each possible sequence of actions on the taget e-sevice execution tee coesponds to possible sequences of actions on the community e-sevice execution tees, suitably inteleaved.

33 Daniela Beadi Example of composition Community e-sevices Sevices (expessed as FSMs) a b S 1 S 2 Taget e-sevice (again expessed as FSM) S 0 a b

34 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b

35 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b All e-sevices e stat fom thei stating state

36 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b Each action of the taget e-sevice is executed by at least one of the component e-sevicese

37 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b When the taget e-sevice e can be left, then all component e-sevices e must be in a final state

38 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b

39 Daniela Beadi Example of composition S 0 S 1 S 2 a b a b coodinating pogam (composition) a b a b a b

40 Daniela Beadi ALC encoding Taget e-sevice S 0 = (Σ, S 0, s 0 0, δ 0, F 0 ) s v s' fo all pais of distinct states in S 0 e-sevice states ae pai-wise disjoint s v a.> u a.s' fo each s'=δ 0 (s,a) taget e-sevice can do an a-tansition going to state s s v a. fo each δ 0 (s,a) undef. F 0 t s F0 s taget e-sevice cannot do an a-tansition denotes taget e-sevice final states

41 Daniela Beadi ALC encoding (cont.d) Community e-sevices S i = (Σ, S i, s 0 i, δ i, F i ) s v s' fo all pais of distinct states in S i e-sevice states ae pai-wise disjoint s v a.(moved i u s' t moved i u s) fo each s'=δ i (s,a) if e-sevice moved then new state, othewise old state s v a. ( moved i u s ) fo each δ i (s,a) undef. if e-sevice cannot do a, and a is pefomed then it did not move F i t s Fi s denotes community e-sevice final states

42 Daniela Beadi ALC encoding (cont.d) Additional assetions a.>v a. t i=1,,n moved i fo each action a at least one of the community e-sevices must move at each step F 0 vu i=1,,n F i when taget e-sevice is final all comm. e-sevices ae final Init s 0 0 u u i=1.n s0 i Initially all e-sevices ae in thei initial state

43 Daniela Beadi DPDL encoding Φ = Init ([u]φ 0 i=1,,n [u]φ i [u]φ aux ) Initial states of all e-sevices DPDL encoding of i-th component e- Sevice DPDL encoding of taget e-sevice DPDL additional domain- independent conditions DPDL encoding is polinomial in the size of the e-sevice e FSMs

44 Daniela Beadi DPDL encoding Taget e-sevice S 0 = (Σ, S 0, s 0 0, δ 0, F 0 ) in DPDL we define Φ 0 as the conjuction of: s s' fo all pais of distinct states in S 0 e-sevice states ae pai-wise disjoint s <a>> [a]s' fo each s'=δ 0 (s,a) taget e-sevice can do an a-tansition going to state s s [a] fo each δ 0 (s,a) undef. F 0 s F0 s taget e-sevice cannot do an a-tansition denotes taget e-sevice final states

45 DPDL encoding (cont.d) Community e-sevices S i = (Σ, S i, s 0 i, δ i, F i ) in DPDL we define Φ i as the conjuction of: s s' fo all pais of distinct states in S i e-sevice states ae pai-wise disjoint s [a](moved i s' moved i s) fo each s'=δ i (s,a) if e-sevice moved then new state, othewise old state s [a]( moved i s ) fo each δ i (s,a) undef. if e-sevice cannot do a, and a is pefomed then it did not move F i s Fi s Daniela Beadi denotes community e-sevice final states

46 Daniela Beadi DPDL encoding (cont.d) Additional assetions Φ aux <a>> [a] i=1,,n moved i fo each action a at least one of the community e-sevices must move at each step F 0 i=1,,n F i when taget e-sevice is final all comm. e-sevices ae final Init s 0 0 i=1.n s 0 i Initially all e-sevices ae in thei initial state DPDL encoding: Φ = Init [u](φ 0 i=1,,n Φ i Φ aux )

47 Daniela Beadi Results Thm: Composition exists iff DPDL fomula Φ SAT Fom composition labeling of the taget e-sevice one can build a tee model of the DPDL fomula and vicevesa Infomation on the labeling is encoded in pedicates moved i Composition existence of e-sevices expessible as FSMs is decidable in EXPTIME

48 Daniela Beadi Results on Finite State Composition Thm: If composition exists then Mealy composition exists. Fom a small model of the DPDL fomula Φ, one can build a Mealy machine Infomation on the output function of the machine is encoded in pedicates moved i Finite state composition existence of e-sevices expessible as FSMs is decidable in EXPTIME

49 Daniela Beadi Summay: The Roman Activity Based Model fo e-sevices Sevice: on-line music stoe select mp3 seach mp3 Client inteacts seach mp3 select mp3 add to cat buy choice points: the e-sevice makes always the client decide what to do next (in pinciple, all states can be choice points). listen states at which client can stop states at which client cannot stop

50 Summay: Automatic e-sevice composition in the Roman Famewok Daniela Beadi But: what if thee does not exist an e-sevice on-line music stoe? the only available e-sevices ae jukebox and bank? Community of e-sevices: jukebox seach mp3 seach mp3 select mp3 bank add to cat add to cat buy listen

51 Summay: Automatic e-sevice composition in the Roman Famewok (cont.d) Taget e-sevice (client equest): on-line music stoe Community of e-sevices (available e-sevices): jukebox, bank based on tableau techniques fo DLs e-sevice Automatic Composition Engine Domain indep. constaints Delegato (delegates each action of taget e- Sevice to e-sevice(s) in the community): Daniela Beadi select mp3 jukebox seach select add to mp3 mp3 cat jukebox jukebox bank listen jukebox seach mp3 jukebox buy bank