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 Macêdo 2 Daniela Barreiro Claro 1 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  Motivation  Dependability requirements for WSC  The SAREK approach  Experimental tests  Performance evaluation  Comparison with related work  Conclusion and future directions Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 2 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK 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. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 3 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 4 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 5 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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 service  partially operational WS  Internet disconnections  Some mechanisms have been introduced  FT-SOAP, WS-Reliability, WS-Replication, etc Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 6 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Required Properties for WSC  Data Consistency  WSC should guarantee the integrity of data in its execution  Computation 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  Scalability  WSC ability to handle a growing amount of WS  Transparency  WS is included and removed from a composition in a transparent way Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 7 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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 Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 8 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

The SAREK Approach  SAREK is a modified and enhanced version of SPOC 1  SAREK is divided into two modules  The Planner Module  Aims to automatically determine the activities for a given composition  The Executor Module  Aims to execute the composition defined by the Planner  Both modules are replicated using a passive replication mechanism. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 9 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach 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

Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 10 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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 request Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 11 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

The Planner Module  The Optimization phase  Optimizes the combination of WS and activities  The values used to optimize are based on estimated values retrieved from each candidate Web service  It seems a quotation system  Produces a set of semantic similar compositions  We used a genetic algorithm called NSGA-II to get the Pareto optimal solutions, i.e. the compositions Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 12 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

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 scheme  Transactional Level Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 13 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

The Executor Module  Semantic replication scheme  Faulty 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 performance  Only the failed partition of the composition is re- executed and the prefix. It saves recovery time supposing that the service s 3 failed. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 14 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

The Executor Module  Transactional Level  Temporal 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 service  Using ACID or a compensation technique Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 15 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Experimental Tests  Case Study  SAREK 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 and MySQL Database 4.1  Experiments were carried out in single computer  Inter motherboard Core Duo, processor T Ghz and 1Gb of RAM. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 16 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Simulated scenario  4 activities  supplyWood, supplyConcrete, supplyIron and buildStaircase  Each activity can be performed by 2 candidate services Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 17 Outline Motivation Properties for WSC SAREK approach Experimental Tests Performance Evaluation Comparison with Related Work Conclusion

Simulated scenario  There is one WSDL operations for execution  String executeWS()  Results were produced by 2 runs  Without failures Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 18 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Simulated scenario  With failures (services 5, 3, 6 failed) Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 19 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Performance Evaluation  Each experiment was run 400 times for calculating the average time and standard deviation  Two kinds of experiments  A composition is fixed  A composition is randomly chosen Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 20 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Performance Evaluation  The overhead caused by faults for an increasing the number of forced Web services failures. Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 21 Outline Motivation Properties for WSC SAREK approach Experimental Tests Performance Evaluation Comparison with Related Work Conclusion

Related Work  Comparison in the light of the required dependability properties for automatic WSC Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 22 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Conclusion and future directions  Challenges for achieving Dependable Web service compositions  Suggesting 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 works  Evaluate the fault tolerant mechanism in real scenarios Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme 23 Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Outline Motivation Properties for WSC SAREK approach

Experimental Tests Performance Evaluation Comparison with Related Work Conclusion Thank you! Daniela Barreiro Claro Raimundo Macêdo LaSiD/DCC/UFBa 24 Daniela Barreiro Claro Raimundo Macêdo Dependable Web Service Compositions using a Semantic Replication Scheme Outline Motivation Properties for WSC SAREK approach