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Composition, Performance Analysis and Simulation of Web Services. Senthilanand Chandrasekaran Advisor: Dr. John A. Miller Computer Science Department The University of Georgia. Topical Outline . Introduction Web Services and Web Services Composition Web Services Enabling Technologies

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composition performance analysis and simulation of web services

Composition, Performance Analysis and Simulation of Web Services

Senthilanand Chandrasekaran

Advisor: Dr. John A. Miller

Computer Science Department

The University of Georgia

topical outline
Topical Outline
  • Introduction
    • Web Services and Web Services Composition
    • Web Services Enabling Technologies
    • Issues in Composition of Web Services
  • Web Service Composition
    • SCET System Architecture
    • Composition Representation
    • Discovery of Services
    • Process Specification
    • Process Execution
    • Performance Analysis
    • Simulation
  • Conclusions and Future Work
  • Definition of Web Service
    • A Web service is a software application identified by a URI, whose interfaces and binding** are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via Internet-based protocols. (W3C definition)
  • Service Oriented Architecture (SOA)










  • **- An association between an Interface, a concrete protocol and a data format
introduction contd
Introduction (contd.)
  • Web Services Allow
    • to reuse software components using a Service Oriented Architecture (SOA)
    • to integrate distributed applications
    • to create loosely-coupled applications (as Web services are based on message passing paradigm)
  • Restriction
    • Individual services offer only limited capabilities
  • Full Potential of SOA
    • We need to compose existing services to create new functionality processes

Web Service Composition

  • Is the task of combining and linking existing

Web services to create new Web processes

  • It adds value to the collection of services, by orchestrating them according to the requirement of the problem
  • Types of Composition
    • Static Composition - services to be composed are decided at design time
    • Dynamic Composition - services to be composed are decided at run-time
web services usage scenarios
Web Services Usage Scenarios

Service Requestor

Service Broker

Individual Service



Web Service




Web Service




Invoke WS


Composite Service



Service Providers


Abstract Process




Web service





Web Service




Web service



Concrete Process


Web service


web services enabling technologies
Web Services Enabling Technologies
  • XML Messaging
    • Simple Object Access Protocol (SOAP) -is an XML Messaging Protocol that allows software running on disparate operating systems and different environments to make Remote Procedure Calls (RPC)
  • Web Services Description
    • Web Service Description Language (WSDL) – is a language that defines the interface of a Web service, required for interaction between a requester and a service provider
  • Web Services Registry
    • Universal Description, Discovery and Integration (UDDI) serves as a “business and service” registryessential for the widespread use of Web services
  • Web Service Composition
    • WSFL, XLANG, BPEL4WS, DAML-S are some of the XML languages that have been proposed for specifying a Web service composition
issues in web service composition
Issues in Web Service Composition
  • Representation of a Abstract Web Process
    • Representing/specifying the abstract process in a proper form
  • Discovery and Interoperability of Services
    • Need to manually or automatically search for appropriate services
    • The discovered services should interoperate
  • Process Execution
    • Adopting a suitable technique for executing the composed concrete process
  • Process Monitoring
    • Using a monitoring technique for run time analysis of the Web process execution
  • Efficiency of a Composed Web Process
    • Need to compose processes which are efficient in terms of performance
barnesbookpurchase process scenario
“BarnesBookPurchase” Process Scenario

ISBN, Email Id., ID

price, id



scet service composition and execution tool
SCET (Service Composition and Execution Tool)
  • SCET Allows
    • to compose services statically by modeling the process as a digraph in a graphical designer
    • stores the process description as WSFL based specification
    • allows execution of the composed process using Perl
    • supports a simple execution monitoring feature
    • supports performance estimation using JSIM simulation
composition representation
Composition Representation
  • Similar to Workflow representations, a Web Process in SCET

is represented as a digraph consisting of

    • Activities
      • Represent tasks involved in the process
      • Each activity stores information about the Web service implementing the task (WSDL File Location, Operation, Input Message, Output Message etc.,)
    • Control Links
      • Specify the control flow (sequencing conditions) within the process
      • Currently, SCET supports XOR splits** in the process specification

** An XOR split represents a point in the process, where based on the control flow, one of the several outgoing branches is chosen

composition representation contd
Composition Representation (contd.)
  • Data Links
    • Specify the flow of information between activities
    • Data Routing (SCET)
      • Routes the output data of a Web service to the input of another Web service without modifying the data
    • Data Mapping (Future Work)
      • Maps the output of the first Web service to a subsequent Web service by applying a transformation function (e.g. indexing in an array, extracting a particular field, etc.)




discovery of services
Discovery of Services
  • The Web service which is to implement an activity needs to

be discovered

  • Static Discovery of Web Services (SCET)
    • Composer manually discovers the services from service repositories

(e.g., UDDI registry, ebXML registry, Web sites )

    • Interoperability between services
      • Data Routing
        • The user specifies which Web service’s output needs to be routed to

which Web service’s input (as done in SCET using data links)

      • Data Mapping
        • The user can provide adapters which transforms the output

of a Web service into a form that can be consumed by the

input of another Web service

        • SCET can be enhanced to provide this adapter feature for

performing data mapping

discovery of services15
Discovery of Services
  • Dynamic Discovery of Web Services (Future Work)
    • Automated service discovery from Web service registries
    • Registries need to provide semantic information about services
    • Support for dynamic negotiation of costs, service level agreements and contracts etc.,
    • Interoperability between services
      • Data Routing & Data Mapping
        • Requires understanding the semantics of the service’s inputs and outputs in order to automate the interoperability of discovered services
web service flow language wsfl
Web Service Flow Language (WSFL)
  • SCET uses WSFL for specifying processes
  • WSFL is IBM’s XML language for describing Web Services Composition
  • We have extended WSFL to include QoS specification such as time, cost and reliability
  • Constructs
    • Activity Elements
    • Message Elements

QoS specification


wsfl contd
WSFL (contd.)

Web service information

  • Service Provider Elements
  • Control Link Elements
  • Data Link Elements

Conditional Branching

Data Routing

process execution
Process Execution
  • Centralized approach (SCET)
    • The services involved in the process are

coordinated by a centralized scheduler

    • Advantage
      • Suitable where coordination between

Web services is difficult to be achieved

      • Easy to implement
    • Disadvantage
      • Creates bottle neck at the coordinator as

all messages need to propagate back

and forth between the controller and

other services

  • Distributed approach
    • The entities participating in a composite

service execution coordinate among themselves









process execution contd
Process Execution (contd.)

Perl Web Service Invocation


  • Languages for Execution
    • Perl (SOAP::Lite), Python, Ruby, Java, C#
  • In SCET, Perl Execution Code Generator converts the WSFL based specification to Perl Execution Code
  • Traverses the WSFL process specification (JDOM XML parsing) and converts
    • each activity element to a Perl Web service invocation block
    • each control linkelement to an ‘if’ control statement in Perl
    • each data linkelement to an ‘assignment’ statement (Data Routing)
performance analysis
Performance Analysis
  • Performance evaluation of Web services can help implementers understand the behavior of the activities in a composed process
  • Web services performance evaluation techniques
    • Time Analysis
    • Load Analysis
    • Process Execution Monitoring
performance analysis contd
Performance Analysis (contd.)
  • Time Analysis

Time taken by a Web service

invocation has three


      • Message Delay Time(M)
      • Waiting Time (W)
      • Service Time(S)
    • T(σ) = M(σ) + W(σ) + S(σ), where σ is a Web service
    • Performing tests to measure the above components for each service involved in a process will indicate a measure of their efficiency
performance analysis contd23
Performance Analysis (contd.)
  • Load Analysis
    • Performed by gradually loading

each Web service involved in the

process, and then measuring

their invocation times

    • After a certain load point, the

performance of the Web service will start degrading.

    • This point is the load range to which the Web service is able to perform effectively
performance analysis contd24
Performance Analysis (contd.)
  • Process Execution Monitoring
    • Monitoring the total number of Web service invocations present at a host will help in analyzing the process
    • SCET is capable of visually displaying the expected number of Web service invocations present in Web service σ’s host

(represented by Ln(σ) )

Ln(σ) = W(σn) + S(σn)Sn(σ) = ∑ (T(σi) – M(σi))







Communication between Perl Code and Java Designer

Java SCET Designer

Perl Execution


Java RMI


Java RMI


performance analysis contd25
Performance Analysis (contd.)
  • Difficulties in Conducting Performance Analysis


    • For conducting performance analysis tests, we require the Web services to be managed by the composer
    • If the services involved are real world services (e.g., Flight Booking Service), then performance analysis by conducting real tests is not feasible
    • To overcome these problems, Simulation could be used as an alternative technique to do performance estimation
  • Simulation helps in determining how composed Web services

will perform under various hypothetical conditions

  • Simulation can provide feedback on the process that was composed allowing the composer to modify his process design by
    • Replacing services which do not satisfy the expected simulation service time means, with better Web services
    • Modifying the process structure (control flow) based on the simulation runs

SCET Process






Simulation Model


JSIM Simulation

Feedback from Simulation

simulation contd
Simulation (contd.)
  • The JSIM simulation model takes as input the service time distribution and the mean service time for each activity involved in the process
  • The Simulation Model Generator of SCET converts the WSFL based specification into JSIM Model
  • As both WSFL process and JSIM Model are represented as digraph the mapping is done as follows

WSFL process

JSIM Model



Control Links



Simulation Entity

simulation contd28
Simulation (contd.)






  • Issues and Problems
    • Static composition
      • Users need to discover services manually analyzing the Web service descriptions provided by the service provider
    • Dynamic composition
      • Dynamic discovery requires Web service Descriptions and Web service registries need to provide more semantic description
    • Control Flow and Data Flow Among Services
      • Need to support control flow constructs such as XOR splits, XOR joins, AND splits, AND joins, and WHILE loops in the process composition
      • In static compositions the composer manually specifies the Data Routing/Mapping between services, while in dynamic compositions the machine has to automate this task
conclusion contd
Conclusion (contd.)
  • Process Execution and Performance Estimation
    • Processes need to be executed and their performance needs to be estimated
  • Results from Test bed Studies
    • Development of the SCET prototype, which isused to represent and specify service composition in WSFL
    • Enhanced WSFL to include QoS attributes, for the activities in the process
    • Implemented the centralized process execution model using Perl, providing simple process execution monitoring feature
    • Time Analysis approaches for estimating the efficiency of the process have been explored
    • Simulation has been used as an alternative technique to analyze a process under various conditions
future work
Future Work
  • SCET needs to be enhanced to support dynamic composition
  • BPEL4WS is a newly proposed composition standard for Web services. SCET needs to be enhanced to support BPEL4WS
  • SCET currently supports only XOR Splits. It needs to be improved to support AND Splits and AND Joins
  • Data links in the process currently provide only Data Routing functionality. Data Mapping feature has to be included with Data links
  • Need to improve the Perl execution code generator, which is currently capable of handling only services which return primitive data types
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web service message protocol soap
Web Service Message Protocol - SOAP
  • SOAP is a lightweight protocol for exchange of information in a decentralized, distributed environment. It is an XML based protocol that consists of three parts: an envelope that defines a framework for describing what is in a message and how to process it, a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing remote procedure calls and responses.




WSFL Based Process specification

Message definitions

Statically configured

Service Providers

Activity definitions

wsfl based process specification contd
WSFL Based Process specification(contd.)

ControlLink definitions

DataLink definitions

perl process execution code
Perl Process Execution Code


Web service Invocation


Web service Invocation


Web service Invocation