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1
Composition, Performance Analysis and Simulation of
Web Services
Senthilanand Chandrasekaran
Advisor: Dr. John A. Miller
Computer Science Department
The University of Georgia
2
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
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Introduction 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)
Service Provider
ServiceRequestor
Service Registry
Find
Bind
Publish
**- An association between an Interface, a concrete protocol and a data format
4
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
Introduction (contd.)
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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 Service Composition
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Web Services Usage Scenarios
RemoteWeb ServiceRepository
Remote Web service
Remote Web service
Remote Web service
Service RequestorIndividual ServiceInvocation
Composite ServiceExecution
PublishWeb Services
Web ServiceLookup
Invoke WS
Compose Abstract Process
Web ServiceLookup
Execute
Search
Invoke
Search
Execute
(SOAP)
SOAP
(SOAP)
(SOAP)
(WSDL)
(UDDI)
WSFL Service Providers
Service Broker
Compose Concrete Process
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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” registry essential 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
Web Services Enabling Technologies
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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
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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
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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
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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.)
Composition Representation (contd.)
WS1 WS2Data
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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 Services
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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
Discovery of Services
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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(time,cost,reliability)
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WSFL (contd.)
Service Provider Elements
Control Link Elements
Data Link Elements
Web service information
Data Routing
Conditional Branching
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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
C
WS1
WS2
WS3
C
WS1 WS2 WS3
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Process Execution (contd.)
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 link element to an ‘if’ control statement in Perl each data link element to an ‘assignment’ statement (Data Routing)
Perl Web Service InvocationBlock
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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
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Performance Analysis (contd.)
Time Analysis
Time taken by a Web service
invocation has three components:
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
Time Analysis
00.5
11.5
22.5
33.5
Services
Tim
e (s
eco
nd
s)
Queue Time
Message DelayTime
Service Time
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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
0
2
4
6
8
10
0 10 15 20 25 30 35
No. of simultaneous load requests
Tim
e (
seco
nd
s)
BarnesGetPrice
CheckCredit
SendLowCreditInfo
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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))
Sn(σ)n
i=1
n
Performance Analysis (contd.)
¯
¯
Java RMI Server
Java SCET Designer
Perl Execution Controller
Java RMI Client
Communication between Perl Code and Java Designer
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Performance Analysis (contd.)
Difficulties in Conducting Performance Analysis Tests
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
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Simulation
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 ProcessComposition
Execution
Feedback from Simulation
JSIM SimulationSimulation Model Generator
WSFL JSIM
Model
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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
Activity Facility
Control Links Transports
Execution Simulation Entity
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Conclusion 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
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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 is used 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
Conclusion (contd.)
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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 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.
Header
Body
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WSFL Based Process specification
Message definitions
Statically configured Service Providers
Activity definitions
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Perl Process Execution Code
BarnesGetPriceWeb service Invocation
CheckCredit Web service Invocation
CheckInventory Web service Invocation