Service Composition, Adaptation, Service Composition, Adaptation,

and Repair

1

Dr. Yuhong Yan

Concordia University, Montreal

Nov. 2, at CASCON2010

Content

� Classification of Web Service Composition Problems

� Sample algorithms for Web Service Composition

� From my research

1. Repair composition for adapting to changes

2. A general composition model for solving different

composition problemscomposition problems

2

Automated Service Composition

� Requirements Specification

� Discovery

� Selection

� Composition

� Monitoring

3

The Composition Algorithm

Composition Alg

Models of Available Services(WSDL, BPEL) Business Process

(BPEL or others )Composition Alg

Composition Requirements(Target processor /and its properties, QoS)

(BPEL or others )

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A Classification of the WSC Problem� WSC: Web Service Composition

� Interface (signature, stateless behavior): WSDL, OWL-S, SAWSDL

� Process (conversation, protocol, stateful behavior): (Abstract)

BPEL, WS-CDL, (automata, process algebra, Petri nets, etc.)

Interface+Reachability Process+Reachability

Composition Requirements

Interface+Reachability Process+Reachability

Interface AI planning,

heuristic search,

dynamic programming,

linear programming, etc.

service matching, 1-1

substitution, process

reconfiguration [Dusdar,

et. al.], [Fredj, et. al.],

[Cavallaro, et. al.])

Process AI planning/Model

checking (e.g. [Pistore])

Adaptor ([Grefen], […])

Roman Model ([Berardi

et. al.])

Mealy Services ([Fu,

Bultan, Su])

Services Models

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Interface – Interface ProblemInterface – Interface Problem

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Service Model: Interfaces

� A Web service: w(in) = out

Add semantics: in ⊆ D, out ⊆ D� Add semantics: in ⊆ D, out ⊆ D

� DSS(D, RD): Data Semantics Structure

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Service Model: Interfaces

� A Web service: w(in) = out

Add semantics: in ⊆ D, out ⊆ D� Add semantics: in ⊆ D, out ⊆ D

� DSS(D, RD): Data Semantics StructureData

Adaptation

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Composition Requirements

� Query: (Din, Dout)

� Reachability properties: terminate properly (end at

desired final state, no deadlock)

� The solution

Din Dout

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An example

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An example (2)

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Map WSC to AI Planning Problem

� A planning problem P = ((S, A, γ), s0, g)� S ⊆ 2L, L = {p1, p2, …, pn} of proposition symbols

� γ(s,a) = s + effects+(a) - effects-(a), a∈A, pre(a) ⊆ s

� s0∈S and g ⊆ L

� A WSC problem P = (W, Din, Dout) can be mapped to a

planning problem ((S, W, γ), Din, Dout)planning problem ((S, W, γ), Din, Dout)

� If in(w) ⊆ s, γ(s, w) = (s-in-(w) + out(w))� STRIP like, propositions only

� We also have the operations made by DSS

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GraphPlan (Blum and Furst, 1997)

w1

E

A

B

C

A

B

C D

w4D

E

F

A

B

C

D

G

E

F

A

B

C

D

H

G

w2

w3

w2

w3

E

F

w4D

J

I

K

L

H

G

J

I

H

P0 A1 A2 A3P2P1 P3

w1w1

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Other Methods

� Dynamic Programming

� Linear Programming

� Heuristic search

See Papers of Web Service Challenge

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Process – Interface ProblemProcess – Interface Problem

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Example – [Pistore, et. al. 2004-2010]

Adaptor?

From Pistore's presentation at FSM0916

Web Services as Stateful Business Processes

From Pistore's presentation at FSM0917

Composition Requirements

� Produce required data outputs

� Reachability: conditions at the goal state (in temporal

logic)

� terminate properly

� recovery conditions

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The Automated Composition Approach

From Pistore's presentation at FSM0919

The Automated Composition Approach

From Pistore's presentation at FSM0920

The Adaptor Problem [Grefen][…]

� Service Model: process

� Composition Requirement: no deadlock in comm

� Calculate adaptor:

� Adaptor is the mediator between the services;

� No services are changed, or replaced;

� Methods: � Methods:

�Consider incompatibility, replaceability,

controllability

�Data matching

�Mismatching tree

�Pattern analysis

�Modeling checking, planning, automata theory based

approaches.

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Adaptor vs. Composition

� Adaptor:

� To facilitate communication

� Strategy: addition

�Not to change the services or target process

�Actions are to bridge the communications

� Properties:� Properties:

�Controllability, compatibility, reachability (no

deadlock)

� Composition:

� To reach the business goals

� Strategy: creation (generate new process)

� Properties: reachability (no deadlock, property satisfaction)

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Hypothesis

� Controllability is a precondition of existence of

composition solution

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Interface – Process Problems

� Service Substitution Problem [Dusdar, et. al.], [Fredj,

et. al.], [Cavallaro, et. al.]

� Strict 1-1 replacement

� m-n replacement

� Reconfiguration Problem

� Compatibility: subsumption, equivalence� Compatibility: subsumption, equivalence

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Process-Process Problem

�Roman Model ([Berardi et. al.], [Calvanese, et. al.,

2008] )

�Mealy Services ([Fu, Bultan, Su])

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My Research (1): Repair Composition in a

Dynamic WorldDynamic World

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Model the Changes

� Changes happen all the time in the real-open world

� Environment Changes: W’ = W + W+ - W-

� Goal Changes: Dout’ = Dout + Dout+ - Dout

-

� We can solve the new problem P=(W’, Din, Dout’)

� By re-planning: planning from scratch� By re-planning: planning from scratch

� By repairing: adapt the original solution to the new problem

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The Repairing Approaches

� The graph built for the original plan is a model of the world

� The original graph is still largely valid for the new problem

� We want to reuse the knowledge in the graph

� We want to keep our commitments in the old solution (solution stability)(solution stability)

Definition of Plan stability [Fox, et. al., 2006]: given two plans π1 and

π2, the difference between π1 and π2 is the number of actions that

appear in π1 and not in π2 plus the number of actions that appear in

π2 and not in π1.

The Repair Process

P’=(W’, Din, Dout’), π', G’

Compute {BPi} Output π

{BPi}=∅, Dout' issatisfied

Repair {BPi} and G’

G’ contains a solution?

Extract a solution

Report no solutionN

Y

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The Repairing Approaches (2)

� After removing Web services, the non-satisfied inputs are named “Broken Preconditions” or BPs

� Main idea:

� Locate the BPs in the existing plan

Select Web services to fix BPs� Select Web services to fix BPs

� Possible fix� Find a replacement: W1 <-> W11

� Find a new service using the original graph

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Illustrate the Principle

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Illustrate the Principle (2)

3232

Repairing Algorithm by Example

G2E H2I

a, b, c, d, f, g, h

A2BC A2D D2F

a, b, c, d, f, g, h, e, i

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A2BC D2F

A2D F2G

C2E F2H

D2E G2E

H2I

A2BC A2D

a, b, c, d, g

A2BC A2DD2F

a, b, c, d, f

a

F2G F2HA2BC A2D D2F

C2E D2E

H2E

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The Service Evaluation Functions

� To evaluate which service to add first:

� n is the highest action level

� m=n to repair the broken goals

� m<n to repair lower

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The Repairing Algorithm

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More Remarks

� The complexity of repairing the graph

� To know a repair exist or not: polynomial to |W|.

� To exact a repair: see below.

� The complexity of plan extraction from the graph

� Without negative effect (based on [Hoffman and Bebel, 2001]) :

polynomial to |W|, max(out(w)), polynomial to |W|, max(out(w)),

� With negative effects ([Blum and Furst, 1996]): exponential |W|

� When repair is better than recomposition?

� If the changes are not too big (can reuse the graph)

� If a replacement service (or services) can be easily found (no need to

search for a complete new plan)

� But we do not know the boundary.

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Datasets Used in ExperimentsDatasets Used in Experiments

4 sets of solutions1 sets of

solutions

1 sets of

solutions

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Experiments and results

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Conclusion

� Repairing plan: an adaptation mechanism to Web

service compositions

� Proposed composition adaptation comparison criteria

� Repair is faster and gets as good solutions as

replanning

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My Research (2): a General Model for

Composition and AdaptationComposition and Adaptation

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Workflow

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Service Model

� Service w = (operations O, WFo)

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Service Model

� Service w = (operations O, WFo)

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Service Model

� Service w = (operations O, WFo)

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Data Semantic Structure

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Data Semantic Structure

� DSS = Concept + Relation

� Relation: cast or composition

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Required Workflows

� Req = (Din, Dout, WFK )

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Encoding

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Encoding

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Encoding

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Tool: pycomposition

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Conclusions:

� Composition and adaptation

� What are interesting topics?

� Composition in a dynamic world

� Unified solution to different WSC problems.

� Unified solution to composition and adaptation

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Questions?

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