ottawa ieee-cs seminar - july 10, 2003 1 web service offerings language (wsol): characteristics,...

1

Ottawa IEEE-CS Seminar - July 10, 2003

Web Service Offerings Language (WSOL): Characteristics, Applications, and Tools

Presenters: Kruti Patel, M.A.Sc.Vladimir Tosic, Ph.D. candidate

(work with Professor Bernard Pagurek)Department of Systems & Computer

EngineeringCarleton University, Ottawa, Canada

[email protected]@sce.carleton.ca

http://www.sce.carleton.ca/~vladimir/WSOLpublications.html

2


Outline

=> Definition of terminologyProblem that WSOL addressesClasses of service and service offeringsWSOL language constructs and examplesThe Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL benefitsFuture work

3


Definition of Terminology

Web Service (WS) - software application Identified by URIs Using XML messaging, description, and

discovery

Web Service composition (orchestration, choreography, flow, network)

Consumer(Requester)

WS

Provider(Supplier)

WS

AnotherWS

4


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

5


WSM and WSCM

Web Service Management (WSM) Management of Web Services from the same

domain of responsibility Measurement and calculation of QoS metrics,

evaluation of conditions, accounting and billing, control of the behavior of the Web Service

WS Composition Management (WSCM) Management of how Web Services co-operate Which WS co-operate in a composition What contracts (e.g., SLAs) are used

6


Outline => Problem Definition ...

Definition of terminology

=> Problem that WSOL addressesClasses of service and service offeringsWSOL language constructs and examplesThe Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL

benefitsFuture work

7


The Need for More Comprehensive Description of WS

WSDL does not formally describe important management information: classes of service, SLAs, other contracts relationships between classes of service different types of constraint (e.g., QoS) other management statements

(prices/penalties, management parties), policies

=> Our solution: WSOL (Web Service Offerings Language)

8


WSOL - Further Goals

Usability for WSM and WSCM

Lower run-time overhead The “simple consumer” assumption

Reusable specifications

Compatible with WSDL 1.1Defined using XML Schema

9


WebService

• Functionality(interfaces)• Access methods(bindings)• Location

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

WSDLdocument

WSOL document

WSOL Complements WSDL

10


Outline => Classes of Service & Service Offerings ...

Definition of terminologyProblem that WSOL addresses

=> Classes of service and service offeringsWSOL language constructs and examplesThe Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL

benefitsFuture work

11


Classes of Service for One Web Service

Discrete variations of service and QoSSame functionality (WSDL description),

but differ in constraints, prices, and/or other management issues For different consumer Web Services With different utilization of the underlying

resources

Service Offering (SO) - a formal WSOL specification of a class of service for a Web Service

12


Possible Differences between Classes of Service

Web Service

class of service 1 class of service 2 …Usage privilegesQuality, verbosity, and/or formatting of resultsGuaranteed response time / Rate and priority of

notificationPayment models (pay-per-use, subscription)Prices and/or penalties for broken guaranteesEntities involved in monitoring and management ...

13


Classes of Service vs. Potential Alternatives

Alternatives: customized SLAs, user profiles, parameterization, separate ports, …

Not a complete replacement for alternativesAn additional and complementary mechanism

Main advantages: relatively low overhead and limited complexity of required management

14


Outline => Language Constructs ...

Definition of terminologyProblem that WSOL addressesClasses of service and service offerings

=> WSOL language constructs and examplesThe Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL benefitsFuture work

15


Overview of WSOL Language Constructs

Service Offering (SO) - class of service constraints (functional, QoS, access rights)

expressions (Boolean, arithmetic, …)

statements (prices/penalties, management responsibility)

reusability constructs (extension, constraint groups, inclusion, instantiation of constraint group templates, …)

Service Offerings Dynamic Relationships (SODRs) - can change during run-time

16


ConstraintA condition to be evaluated before/after

operation invocations or periodically Contains a Boolean expression

Supported categories of constraints: Functional (pre-, post-, and future-conditions) QoS (non- or extra-functional) and periodic

QoS - using external ontologies of QoS metrics Simple access rights Generic <constraint> construct

17


Expressions in WSOLBoolean expressionsComparisonsArithmetic expressionsArray expressions - quantifiers ForAll &

ExistsString expressions (limited)Date/time and duration expressions

(limited)Operation calls to other Web Services or

libraries within constraint evaluators

18


Statement

Information, other than constraint, about the service offering

Supported categories of statements: Price/penalty statements (subscription, pay-

per-use, or combinations) Management responsibility statements

(provider, consumer, 3rd parties) Service offering validity period Generic <statement> construct

19


WSOL Reusability Constructs

Service offering (SO) Constraint group (CG) Constraint group template (CGT) Extension (single inheritance) Inclusion Applicability domain Declaration of an operation call

Declaration of a used QoS metric

20


Constraint Group (CG)

A named set of constraints, statements, reusability constructs, and/or nested CGs Boolean ‘AND’ operation always applied

between constraints, statements Single inheritance (extension) of CGs

possible

Different groupings possible (e.g., aspects)Unit of reusability and management

responsibility

21


Constraint Group Template (CGT)

A parameterized constraint group (CG) Begins with declaration of abstract parameters Parameters can be used in contained expressions

Single inheritance (extension) of CGTs possible

Can be instantiated multiple times with different concrete parameter values

The result of an instantiation is a new CG

22


Service Offering (SO)

Syntax similarities with constraint groups (CGs) Constraints, statements, reusability constructs Single inheritance of service offerings

But, also syntax differences with CGs No nesting of service offerings! Single accounting party

Can be used for many different consumersThe same service offering can be provided by

many Web Services

23


Example WSOL Service Offering<wsol:serviceOffering name="SO1" service=

"buyStock:buyStockService" accountingParty="WSOL-SUPPLIERWS">

… <wsol:instantiate CGTName="CGT2" resService="..."

resPortOrPortType="..." resOperation="..." resCGName="CG5">

<wsol:parmValue name=“maxResTime"> <wsol:numberWithUnitConstant>

<wsol:value>30</wsol:value> <wsol:unit type="QoSMeasOntology:millisecond"/> </wsol:numberWithUnitConstant></wsol:parmValue>

</wsol:instantiate></wsol:serviceOffering>

24


Example: buyStock Web Service

buyStock Web Service

buyStockPortType buySingleStockOperation buySingleStockRequest symbol quantity buySingleStockResponse totalStockBuyingCost … buyStockBindingbuyStockPort

buyStock.wsdl ServiceOffering1

accounting party: supplier Constraint1: preCondition scope: buyStockOperation quantity > 0 Constraint2: QoSConstraint scope: buyStockOperation ResponseTime < 0.5 s Price: 0.5 $ServiceOffering2 …

buyStock.wsol

25


Service Offerings Dynamic Relationship (SODR)

Another WSOL language constructSpecified outside service offeringsSyntax: <SO1, S, SO2> - if SO1 is used, and

S are not met, SO2 is appropriate replacement

Useful for easier selection and negotiation of service offerings

Useful for dynamic adaptation of Web Service compositions

26


Outline => The Premier WSOL Parser ...

Definition of terminologyProblem that WSOL addressesClasses of service and service offeringsWSOL language constructs and examples

=> The Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL

benefitsFuture work

27


The “Premier” WSOL ParserDeveloped in JavaApache Xerces2 Java XML Parser re-usedFeatures:

Implements WSOL language constructs Validates WSOL documents (service offerings

and SODRs) & WSOL-related documents (WSDL & Ontology)

Detects various syntax and semantic errors Reports all the detected errors

Location of each error (file name, line number, etc.)Cause of each error

28


Working of the Premier WSOL Parser

input

WSOL Parser

WSOL-related Documents

WSOL Documents

input

Detects and reports syntax & semantic errors

DOM trees for WSOL &

WSOL-related documents

output

Detects and reports syntax & semantic errors

Multiple Symbol Tables

Stores and retrieves data for semantic analysis

29


WSOL Parser Example - DOM Tree

30


Premier WSOL Parser Example - Detected Syntax Error

31


Outline => Management Applications and Tools ...

Definition of terminologyProblem that WSOL addressesClasses of service and service offeringsWSOL language constructs and examplesThe Premier WSOL parser

=> Management applications and toolsRelated work and summary of WSOL

benefitsFuture work

32


Applications of WSOLWeb Service management: monitoring,

measurement, evaluation, accounting, control Using WSOL service offerings as simple contracts

Dynamic adaptation and management of Web Service compositions Using manipulation of WSOL service offerings

Dynamic selection and negotiation of Web Services and classes of service

33


WSOL Support for Management Functional Areas

QoS constraints - performance mgmt.Price/penalty statements - accounting

managementFunctional constraints - fault managementManagement responsibility statements -

configuration management (part.)Access rights - security management (part.)=> Service offerings - a lightweight

alternative to SLAs and other contracts

34


Management Parties: Example

ConsumerWS

AccountingParty

QoSConstraintEvaluation

Party

MeteringParty Provider

WS

35


Web Service Offerings Infrastructure (WSOI)

Infrastructure for WSOL-related WSM For measurement and calculation of QoS metrics For evaluation of constraints For accounting and billing

Based on open-source Apache Axis SOAP engine Additional modules and data structures

Infrastructure for WSOL-related WSCM Will be discussed in forthcoming slides

36


Dynamic Adaptation Using Manipulation of WSOL SOs

Switching between service offerings Provider- or consumer-initiated

Deactivation and reactivation of SOs With accommodation of affected consumers

Deletion of deactivated SOs Creation of new SOs (same WSDL files)

Provider decides when it is possible and allowed

Deactivation, reactivation, deletion, and creation of SODRs

37


WSOL Support for Manipulation of Service Offerings

Service offerings dynamic relationships (SODRs) - for switching, deactivation, and reactivation of service offerings

Reusability constructs (static relationships between service offerings) - for creation of service offerings, partially for the other mechanisms Examples: extension, inclusion, constraint group

template instantiation

38


WSOI Support for Manipulation of Service Offerings

Special data structures Implementation of algorithms and

protocols for the manipulation of SOsSpecial port types with management

operations for: exchange of management information, manipulation of service offerings, manipulation of SODRs, providing information about available SOs, comparisons of service offerings, …

39


Manipulation of Service Offerings vs. Alternatives

Alternatives: re-negotiation of SLAs, switching of Web Services, re-composition of Web Services, …

Comparisons of delays and memory overhead using analyses and experiments

SO1FA1

SN1

SO2SN2a)

SO1

SO2

FA1

SN1

b)

40


Benefits of Manipulation of Service Offerings

Simpler, faster, and incurs less overhead than re-negotiation of SLAs and switching or re-composition of Web Services

Provides additional flexibilityEnhances robustness of WS

compositions

Not a complete replacement for alternatives Can be used as a lightweight complement

to other dynamic adaptation mechanisms

41


Outline => Related Work & Summary of WSOL Benefits ...

Definition of terminologyProblem that WSOL addressesClasses of service and service offeringsWSOL language constructs and examplesThe Premier WSOL parserManagement applications and tools

=> Related work & summary of WSOL benefits

Future work

42


Some Related Work

Differentiated services (e.g., in telecom)Formal specification of various constraints

Specification of SLAs for Web Services: WSLA (Web Service Level Agreements) - IBM WSML (… Management ...) - HP

WS-Policy - IBM/Microsoft/BEA/SAPDAML-S - the Semantic Web communityOGSA (Open Grid Services Architecture)

43


Summary of Benefits of WSOL ...

Expressive power

Features with lower run-time overhead

Support for management applications

44


Expressive Power

Formal specification of various categories of constraints and management statements

Multiple classes of service per Web Service

Mechanisms for reuse of specificationsDescription of both static and dynamic

relationships between service offerings

Extensibility using XML Schema mechanisms and external ontologies

45


Lower Run-time Overhead

Classes of service

One language for multiple types of constraint and management statements

Support for management third parties

Periodic and occasional evaluation of constraints

46


Support for Management Applications

Formal specification of various constraints and management statements

Specification of management third parties and the specific accounting party

Reusability constructs determine static relationships between service offerings

Special notation for dynamic relationships between service offerings

47


Outline => Future Work ...

Definition of terminologyProblem that WSOL addressesClasses of service and service offeringsWSOL language features and examplesThe Premier WSOL parserManagement applications and toolsRelated work and summary of WSOL

benefits

=> Future work

48


Future Work

Minor improvements of WSOL Full prototype implementation of the Web

Service Offerings Infrastructure (WSOI) Further experiments with the manipulation

of service offerings and alternatives Full implementation of a prototype WSOL

compilerIntegration of WSOL with UDDI and

BPEL4WS…

49


Questions, please ...

For further information: [email protected]

[email protected]/~vladimir/

WSOLpublications.html