dependable web service compositions usng a semantic replication scheme

Dependable Web Service Compositions usng a

Semantic Replication Scheme

LABORATÓRIO DE SISTEMAS DISTRIBUÍDOS – LASID

DEPARTAMENTO DE CIÊNCIA DA COMPUTAÇÃO - DCC

UNIVERSIDADE FEDERAL DA BAHIA - UFBA

SBRC 2008

Raimundo José de Araújo Macêdo2Daniela Barreiro Claro1

1. Dr. Daniela Barreiro Claro is supported by FAPESB (BOL2071/2006).2. Prof. Raimundo José de Araujo Macêdo is supported by FAPESB and CNPQ(Edital Universal).

Outline

MotivationDependability requirements for WSCThe SAREK approachExperimental testsPerformance evaluationComparison with related workConclusion and future directions

Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a [email protected] [email protected] Semantic Replication Scheme 2

Experimental TestsPerformance EvaluationComparison with Related WorkConclusion

OutlineMotivation

Properties for WSCSAREK approach

Motivation

Web services are autonomous applications that can be published, located and invoked over the Internet.

Due to their potential for heterogeneous integration, companies are implementing their business as a Web service format.

However, a single Web service cannot fulfill a user request and need to be combined.



OutlineMotivation


Motivation

Whereas WS specifications cover dependable issues, no one handles the problem of dependable and automatic Web service compositions.

This raises another problem: a single WS failure, thus the failure of the whole composition.

Availability or continuity of service must be taken into account to apply WSC in critical applications.



OutlineMotivation


Motivation

A commonly used technique for improving availability is to replicate services.

This work tackles the problem of dependability requirements of WSC, using ontologies to form a set of semantically alike replicas.

We propose a framework SAREK where a failure of a primary service can be masked by the execution of another service semantically compatible.



OutlineMotivation


Required Properties for WSC

Some kinds of faults should be treated by a fault tolerant mechanism in order to reach the goal of a WSC.unavailability of a Web servicepartially operational WS Internet disconnections

Some mechanisms have been introducedFT-SOAP, WS-Reliability, WS-Replication, etc



OutlineMotivation


Required Properties for WSC

Data ConsistencyWSC should guarantee the integrity of data in its

executionComputation Availability

It is not possible to assume that all WS in a composition are reliable. A WSC should guarantee availability without knowing the reliability level of single WS

ScalabilityWSC ability to handle a growing amount of WS

TransparencyWS is included and removed from a composition in

a transparent way



OutlineMotivation


The SAREK approach

System model and assumptions A set of activities m is the

number of activities. A set of services n is the number

of services. Candidate services is a subset of Service for a

specific activity A composition C is a sequence of activities

performed by a set of services

WS are implemented as processes Channels are assumed to be reliable

]..1[; mjAa j



OutlineMotivation


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jS 'jjj SSa ',

S

mj aaaa ,...,,, 21

ni ssss ,...,,, 21

The SAREK Approach

SAREK is a modified and enhanced version of SPOC1

SAREK is divided into two modulesThe Planner Module

Aims to automatically determine the activities for a given composition

The Executor ModuleAims to execute the composition defined by the Planner

Both modules are replicated using a passive replication mechanism.



OutlineMotivation


1. Claro D.B, Albers P. And Hao, J-K. A framework for automatic composition of RFQ Web services. In IEEE SCW/ WSCA-ICWS, Salt Lake City, USA. 2007



OutlineMotivation


The Planner Module

The Planner is divided into two main phases: Planning and Optimization

The Planning phase It uses an AI Planning algorithm based on preconditions

and effects Interacts with OPS (an OWL ontology) to discover

services Each WS is described using an OWL-S format This phase aims to determine which activity belongs to

the composition in order to fulfill the user request It main issue is the set of activities A that can reach the

given requestDaniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a

[email protected] [email protected] Semantic Replication Scheme 11


OutlineMotivation


The Planner Module

The Optimization phaseOptimizes the combination of WS and activitiesThe values used to optimize are based on estimated

values retrieved from each candidate Web service It seems a quotation systemProduces a set of semantic similar compositionsWe used a genetic algorithm called NSGA-II to get

the Pareto optimal solutions, i.e. the compositions



OutlineMotivation


The Executor Module

This module executes the composition using the prefix mechanism

In order to provide fault tolerance both a transactional approach and a replication mechanism are applied.Semantic replication schemeTransactional Level



OutlineMotivation


The Executor Module

Semantic replication schemeFaulty Web service can be replaced by a

semantically similar service (transparency property)

Kind of spatial redundancy, because there is a set of compositions that achieve the same goal.

The prefix approach increases performanceOnly the failed partition of the composition is re-

executed

and the prefix . It saves recovery time supposing that the service s3 failed.

321 ,, sssC



OutlineMotivation


21, ss

The Executor Module

Transactional LevelTemporal redundancy mechanism, SAREK tries

one more time to recover from a possible transient fault

If the problem persists, and no other semantic similar composition can be replaced, SAREK roll back the previous executed Web serviceUsing ACID or a compensation technique



OutlineMotivation


Experimental Tests

Case StudySAREK was applied to a bidding process for

repairing public buildings.

Prototype implementation of SAREK Java 1.5, Apache Tomcat 5.0, Axis 1.3, Jena API

2.3, OWL-S API 1.1.0 and MySQL Database 4.1Experiments were carried out in single computer

Inter motherboard Core Duo, processor T2300 1.66 Ghz and 1Gb of RAM.



OutlineMotivation


Simulated scenario

4 activitiessupplyWood, supplyConcrete, supplyIron and

buildStaircase

Each activity can be performed by 2 candidate services


OutlineMotivation



Simulated scenario

There is one WSDL operations for executionString executeWS()

Results were produced by 2 runsWithout failures



OutlineMotivation


Simulated scenario

With failures (services 5, 3, 6 failed)



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Performance Evaluation

Each experiment was run 400 times for calculating the average time and standard deviation

Two kinds of experimentsA composition is fixedA composition is randomly chosen



OutlineMotivation


Performance Evaluation

The overhead caused by faults for an increasing the number of forced Web services failures.


OutlineMotivation



Related Work

Comparison in the light of the required dependability properties for automatic WSC



OutlineMotivation


Conclusion and future directions

Challenges for achieving Dependable Web service compositionsSuggesting a set of required dependability

properties.

To the best of our knowledge, SAREK is the first framework that provides such fault tolerant guarantees in WSC

Future worksEvaluate the fault tolerant mechanism in real

scenarios



OutlineMotivation



Thank you!

Daniela Barreiro [email protected]

Raimundo Macêdo [email protected]

http://www.lasid.ufba.br

LaSiD/DCC/UFBa

24Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a

[email protected] [email protected] Semantic Replication Scheme

OutlineMotivation


dependable web service compositions usng a semantic replication scheme

Documents

single web service

web service format

continuity of service

primary service

problem of dependable

raimundo jos

dependable issues

araujo macdo