Characteristics of the Web Service Offerings Language (WSOL)

1
Characteristics of the Web Service Offerings
Language (WSOL)

• Presenter Vladimir Tosic
• (work with K. Patel, B. Pagurek)
• Network Management Artificial Intelligence Lab
  Department of Systems Computer Engineering
• Carleton University, Ottawa, Canada
• vladimir_at_sce.carleton.ca
• http//www.sce.carleton.ca/netmanage/

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Outline

• Definition of terminology
• Problem definition
• Classes of service and service offerings
• WSOL language constructs and examples
• Applications and tools
• Related work and summary of WSOL benefits
• Future work

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WSOL Definition of Terminology

• gt Definition of terminology
• Problem definition
• Classes of service and service offerings
• WSOL language constructs and examples
• Applications and tools
• Related work and summary of WSOL benefits
• Future work

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Definition of a Web Service (WS)

• A unit (component) of business, application, or
  system functionality
• Using XML (Extensible Markup Language) messaging,
  description, and discovery
• Software-based and/or hardware-based
• Goal Internet-wide A2A and B2B integration of
  heterogeneous systems

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Some StandardTechnologies for Web Services

• XML (Extensible Markup Language) - data
  representation
• SOAP (a.k.a. XML Protocol) - message format
• WSDL (Web Services Description Language) -
  language for description of Web Services
• UDDI (Universal Description, Discovery, and
  Integration) - discovery of Web Services

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Other Terms Used in This Presentation

• Web Service composition (a.k.a. orchestration,
  choreography, flow, network)
• Consumer (a.k.a. requester) Web Service
• Supplier (a.k.a. provider) Web Service

Supplier WS
Another WS
Consumer WS
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WSOL Problem Definition ...

• Definition of terminology
• gt Problem definition
• Classes of service and service offerings
• WSOL language constructs and examples
• Applications and tools
• Related work and summary of WSOL benefits
• Future work

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The Need for More Comprehensive Description of WS

• WSDL does not formally describe
• constraints (functional, QoS - Quality of
  Service, access rights)
• service level agreements (SLAs) and other
  contracts between Web Services
• multiple classes of service for one Web Service
• gt Our solution WSOL (Web Service Offerings
  Language)

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WSOL - Further Goals

• Usable for monitoring and management
• Both for Web Service Management (WSM) and Web
  Service Composition Management (WSCM)
• Reusable specifications
• Reduction of run-time overhead
• The simple consumer assumption
• Fully compatible with WSDL

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WSDL vs. WSOL
Web Service
WSDL document
WSOL document

• Various constraints
• Management
• statements
• Multiple classes of
• service for one
• Web Service

• Functionality
• Access
• methods
• Location

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WSOL Classes of Service Service Offerings ...

• Definition of terminology
• Problem definition
• gt Classes of service and service offerings
• WSOL language constructs and examples
• Applications and tools
• Related work and summary of WSOL benefits
• Future work

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Classes of Service for One Web Service

• Discrete variations of service and QoS
• Same functionality (WSDL description)
• Differ in constraints, prices, and/or other
  management issues
• For different consumer Web Services
• With different utilization of the underlying
  resources

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Example buyStock WSClasses of Service
buyStock Web Service
class of service 1
class of service 2

• Usage privileges
• Quality, verbosity, and/or formatting of results
• Guaranteed response time / Rate and priority of
  notification
• Payment models (pay-per-use, subscription)
• Prices and/or penalties for broken guarantees
• Entities involved in monitoring and management
• ...

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Classes of Service vs. Potential Alternatives

• Alternatives customized SLAs, user profiles,
  parameterization, separate ports,
• Not a complete replacement for alternatives
• An additional and complementary mechanism
• Main advantages relatively low overhead and
  limited complexity of required management

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Definition of a Service Offering

• A formal specification of a class of service for
  a Web Service (component-level)
• Contains formal specification of various
  constraints and management statements
• A simple contract and SLA between Web Services
• One Web Service can offer multiple service
  offerings

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WSOL Language Constructs ...

• Definition of terminology
• Problem definition
• Classes of service and service offerings
• gt WSOL language constructs and examples
• Applications and tools
• Related work and summary of WSOL benefits
• Future work

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WSOL Language Features

• Defined using XML Schema
• Compatible with WSDL 1.1
• WSOL constructs
• constraint
• statement
• constraint group (CG)
• constraint group template (CGT)
• service offering

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Constraint

• A condition to be evaluated
• Boolean expression
• Evaluation with operation invocations or
  periodic
• Supported categories of constraints
• Functional constraints (pre-, post-, and
  future-conditions)
• QoS (a.k.a. non- or extra-functional) constraints
  - using external ontologies of QoS metrics
• Simple access rights
• Generic ltconstraintgt construct

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Example WSOL Constraint

• ltwsolconstraint name"C3" xsitype
  "preConditionSchemapreCondition"
  service"buyStockbuyStockService"
  portOrPortType"buyStockbuyStockServicePort"
  operation"buyStockbuySingleStockOperation"gt
• ltexpressionSchemabooleanExpressiongt
• lt/expressionSchemabooleanExpressiongt
• lt/wsolconstraintgt

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Expressions in WSOL

• Boolean expressions
• Comparisons
• Arithmetic expressions
• Array expressions - quantifiers ForAll Exists
• String expressions (limited)
• Date/time and duration expressions (limited)
• External operation calls
• SOAP calls to other Web Services
• Internal calls within constraint evaluators

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Example WSOL Expression

• ltexpressionSchemabooleanExpressiongt
• ltexpressionSchemaarithmeticExpressiongt
• ltexpressionSchemaarithmeticVariable
  avName"buyStockbuySingleStockRequest.quantity"/gt
  
• lt/expressionSchemaarithmeticExpressiongt
• ltexpressionSchemaarithmeticComparator
  type"gt"/gt
• ltexpressionSchemaarithmeticExpressiongt
• ltexpressionSchemaarithmeticConstantgt
• ltexpressionSchemaintegerConstant value"0"/gt
• lt/expressionSchemaarithmeticConstantgt
• lt/expressionSchemaarithmeticExpressiongt
• lt/expressionSchemabooleanExpressiongt

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Statement

• Information, other than constraint, about the
  service offering
• Price/penalty statements
• Subscription, pay-per-use, or combinations
• Management responsibility statements
• Supplier, consumer, 3rd parties
• Inclusion statements
• Instantiations of constraint group templates
• Declarations of external operation calls

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Example WSOL Price Statement

• ltwsolprice name"Price1" service""
  portOrPortType"" operation""gt
• ltwsolnumberWithUnitConstantgt
• ltwsolvaluegt3lt/wsolvaluegt
• ltwsolunit type"currencyOntologymilliDollar"/gt
  
• lt/wsolnumberWithUnitConstantgt
• lt/wsolpricegt

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Constraint Group (CG)

• A named set of constraints, statements, and/or
  nested CGs
• Potential unit of reusability and management
  responsibility
• Single inheritance (a.k.a. extension) of CGs

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Example WSOL CG

• ltwsolCG name"CG7" service"" portOrPortType
  "" operation"..."gt
• ltwsolCG name"CG8" service"" portOrPortType
  "" operation"...gt
• lt/wsolCGgt
• ltwsolconstraint name"C7 gt...lt/wsolconstrain
  tgt
• ltwsolinclude constructName"C3"
  resService"buyStockbuyStockService"
  resPortOrPortType "buyStockbuyStockServicePort"
  resOperation"buyStockbuySingleStockOperation"
  resName"NewC3"/gt
• lt/wsolCGgt

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Constraint Group Template (CGT)

• A parameterized CG
• Begins with declaration of abstract parameters
• Parameters can be used in contained expressions
• Single inheritance of CGTs
• A CGT must be defined outside definitions of
  other CGTs, CGs, and service offering
• Instantiation of a CGT with concrete parameters
  gt a CG

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Example WSOL CGT

• ltwsolCGT name"CGT2" service"" portOrPortType
  "" operation"..."gt
• ltwsolparameter namemaxResTime"
  dataType"wsolnumberWithUnit" unit"QoSMeasOntolo
  gymillisecond"/gt
• ltwsolconstraint name "QoScons2" gt
• ltexpressionSchemabooleanExpressiongt
• ltexpressionSchemaarithmeticExpressiongt
• ltexpressionSchemaQoSmetric
  metricType"QoSMetricOntologyResponseTime
  service"" portOrPortType "" operation"...
  measuredBy"WSOL_INTERNAL"/gt
• lt/expressionSchemaarithmeticExpressiongt
• ltexpressionSchemaarithmeticComparator type
  "lt"/gt
• ltexpressionSchemaarithmeticExpressiongt
• ltexpressionSchemaarithmeticVariable
  avName"tnsCGT2.maxResTime"/gt
• lt/expressionSchemaarithmeticExpressiongt
• lt/expressionSchemabooleanExpressiongt
• lt/wsolconstraintgt
• lt/wsolCGTgt

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Syntax of a Service Offering

• Similar to a CG constraints, statements, CGs
• Single inheritance of service offerings
• No nesting of service offerings!
• Use CGs instead
• Single accounting party

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Example WSOL Service Offering

• ltwsolserviceOffering name"SO1" service
  "buyStockbuyStockService" accountingParty"WSOL-S
  UPPLIERWS"gt
• ltwsolinstantiate CGTName"CGT2"
  resService"..." resPortOrPortType"..."
  resOperation"..." resCGName"CG5"gt
• ltwsolparmValue namemaxResTime"gt
• ltwsolnumberWithUnitConstantgt
• ltwsolvaluegt30lt/wsolvaluegt
• ltwsolunit type"QoSMeasOntologymillisecond"
  /gt
• lt/wsolnumberWithUnitConstantgt
• lt/wsolparmValuegt
• lt/wsolinstantiategt
• lt/wsolserviceOfferinggt

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Example buyStock Web Service
buyStock Web Service
buyStock.wsdl
buyStock.wsol
ServiceOffering1 accounting party supplier
Constraint1 preCondition scope
buyStockOperation quantity gt 0 Constraint2
QoSConstraint scope buyStockOperation
ResponseTime lt 0.5 s Price 0.5
ServiceOffering2
buyStockPortType buySingleStockOperation
buySingleStockRequest symbol
quantity buySingleStockResponse
totalStockBuyingCost buyStockBinding buySt
ockPort
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WSOL Support for Reuse of Specifications

• To model similar, but somewhat different, classes
  of service
• Supported reuse mechanisms
• Inclusion statements
• Specialization of scope (for inclusion,
  instantiation)
• Grouping CGs, CGTs, and service offerings
• Nesting of CGs
• Single inheritance (a.k.a. extension) CGs, CGTs,
  and service offerings
• Templates CGTs

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Dynamic Relationships Between Service Offerings

• Dynamic Run-time
• For easier selection and negotiation of service
  offerings
• For dynamic adaptation of Web Service
  compositions
• Specified outside service offerings
• Syntax ltSO1, S, SO2gt

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WSOL Applications and Tools ...

• Definition of terminology
• Problem definition
• Classes of service and service offerings
• WSOL language constructs and examples
• gt Applications and tools
• Related work and summary of WSOL benefits
• Future work

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Applications of WSOL

• Web Service management monitoring, metering,
  accounting, and control
• Contracts and SLAs between Web Services
• Dynamic and autonomous adaptation and management
  of Web Service compositions
• To further increase agility, flexibility,
  adaptability
• Dynamic selection and negotiation of Web Services
  and classes of service

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Example Management Third Parties
Supplier WS
Consumer WS
Accounting Party
Metering Party
QoS Constraint Evaluation Party
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Prototype WSOL Tools

• WSOL parser with syntax checks and some semantic
  checks
• Future work
• Automatic generation of Java constraint-checking
  code from WSOL and WSDL
• Using composition filters and/or other
  aspect-oriented (AO) approaches?
• Java API for generation of WSOL files

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WSOL Related Work Summary of WSOL Benefits
...

• Definition of terminology
• Problem definition
• Classes of service and service offerings
• WSOL language constructs and examples
• Applications and tools
• gt Related work summary of WSOL benefits
• Future work

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Some Related Work

• Differentiated services
• Formal specification of various constraints
• Specification of SLAs for Web Services
• WSLA (Web Service Level Agreements) - IBM
• WSML ( Management ...) - HP
• WSEL ( Endpoint ) - IBM (no detail yet)
• DAML-S - the Semantic Web community
• OGSA (Open Grid Services Architecture)

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Summary of Benefits of WSOL ...

• Expressive power
• Reduced run-time overhead
• Orientation towards management applications

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Summary of Benefits of WSOL Expressive Power

• Formal specification of various categories of
  constraints and management statements
• Multiple classes of service per Web Service
• Mechanisms for reuse of specifications
• Description of both static and dynamic
  relationships between service offerings
• Extensibility through external ontologies of QoS
  metrics and measurement units

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Summary of Benefits of WSOL Reduced Run-time
Overhead

• Classes of service
• One language for various constraints
• Metering and monitoring of WSOL specifications
  can be done by 3rd parties
• SOAP intermediaries or probes
• Reasoning about WSOL service offerings can be
  outsourced to specialized Web Services

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Summary of Benefits of WSOL Management
Applications

• Simple contracts and SLAs that can be monitored,
  metered, and controlled
• Manipulation of service offerings useful in both
  Web Service Management (WSM) and Web Service
  Composition Management (WSCM)
• Development of tools in progress

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WSOL Related Work Summary of WSOL Benefits
...

• Problem definition
• Classes of service for one Web Service and
  definition of a service offering
• WSOL language features and examples
• Applications and tools
• Related work and summary of WSOL benefits
• gt Future work

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Future Work

• Improved tools
• Improved syntax
• Research of Web Service Composition Management
  (WSCM) applications of WSOL
• Compatibility with WSDL 1.2
• Compatibility with BPEL4WS (Business Process
  Execution Language for Web Services)

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Questions, please ...