Dynamic Adaptation of Service Compositions Using Service

Offerings

Presenter: Vladimir Tosic (work with K. Patel, B. Pagurek, B. Esfandiari)Network Management & Artificial Intelligence

Lab Department of Systems & Computer Engineering

Carleton University, Ottawa, Canada

Outline

Introduction to service-based software systems Overview of goals, definition of terminology, and an

example

Our research Research goals and our approach Service offerings and WSOL Dynamic adaptation capabilities The example revisited Current status and future work The DAMSC infrastructure

Conclusions; questions and answers

Service-Based Software Systems

“Software is a service” business modelApplications decomposed into distributed

components - services

Different terminology: service components, Web Services, e-services, dynamic services, eUtilities, …

Web Services industrial initiatives from Microsoft, IBM, HP, Sun, Oracle, …

Standards by W3C (World Wide Web Consortium)

Some Goals of the Work on Web Services

Faster development of complex software systemsFlexible, adaptable, and agile business

relationshipsAd hoc A2A (Application-to-Application) and B2B

(Business-to-Business) integration

Interoperability of heterogeneous Web ServicesLeveraging existing Internet/Web infrastructure;

based on XML (Extensible Markup Language)“Scalability to the Web”

=> Application area: e- and m-business systems

Definition of aService Component

A unit of service provisioning and management Encapsulates some service functionality and

appropriate dataSoftware-based and/or hardware-based

Composable, reusable, and replaceableMain use - service compositionsSupplier and consumer

A special case: Web Service

Example

An m-commerce system built from third-party pay-per-use service components

UserManager

ProductInfoRepository

ProductStockManager

OrderManager

Server(includes ShoppingCart states)

ClientInteraction

CreditCardVerification

Our Research Goals

Service compositions have to be managedDynamic and autonomous adaptation is one

management activityApproaches based on finding alternative service

components are not always appropriate

We work on additional and complementary support within service components to dynamically and autonomously adapt the composed

service components and their relationships, without breaking these relationships

Our Approach

Dynamic adaptation using manipulation of classes of service Introduce the concept of classes of service for

service components (extrapolate the corresponding concepts from telecommunications)

Develop appropriate adaptation capabilities & algorithms

Implementation-independent solutions and their mapping to Web Services

Appropriate infrastructure and its prototypes

Multiple Classes of Service

Variations of service and QoS (Quality of Service)

Same functionality, but differ in constraints functional constraints non-functional (QoS) constraints authorization policies cost …

Increase chances to succeed in the market by broadening the market segment

Enable balancing limited underlying resources, as well as the price/performance ratio

A Service Offering

A formal specification of a class of serviceAllowed combinations of interface-level service

offerings determine component-level service offerings

Specified separately from the specification of functionality

Constraint dimensions are separated for easier specification, but integrated into service offerings for easier choice by consumers

Specification of relationships between service offerings is a very important issue

Service Offerings vs. Potential Alternatives

Various potential alternativesService offerings are an additional &

complementary mechanism for differentiation of service and QoS

Not a complete replacement for alternatives

Advantages of service offerings include: additional flexibility relatively low overhead limited complexity of required management support for dynamic adaptation mechanisms

WSOL - Web Service Offerings Language

Explicit and formal specification of various constraints and service offerings for Web Services in XML supports dynamic selection of Web Services minimizes unexpected feature interactions

Extends WSDL (Web Services Description Language)

We are working on prototypes for: a WSOL parser with syntax and some semantic checks (automatic generation of WSOL files using Java) (Java code generation from WSOL and WSDL specifications)

Reusing and extending existing Web Services tools

WSOL - Current Status& Future Work

WSOL prototype parserCurrent issue: functional constraints that

include complex expressionsFuture work: other constraints, particularly

different dimensions of QoS

Separation and integration of constraint dimensions is the main open issue

Relationships between service offerings will be specified using a combination of constraint dimensions and roles

Motivation for Dynamic Adaptation Capabilities

Goal: accommodate changes without breaking relationships between service components

Based on dynamic manipulation of service offerings

Cannot completely replace finding alternative service components, but a useful complement

Advantages include: adaptation speed enhanced robustness of relationships between service

components simplicity and relatively low overhead

ThreeDynamic Adaptation Capabilities

1. Switching between service offerings Initiated by the service component or its consumers

2. Deactivation/reactivation of service offerings With automatic accommodation of affected

consumers

3. Creation of new appropriate service offerings Not creation of new functionality The service component decides when it is possible

and allowed

The M-Commerce System Example Revisited

Benefits of service offerings and the suggested dynamic adaptation mechanisms

UserManager

ProductInfoRepository

ProductStockManager

OrderManager

Server(includes ShoppingCart states)

ClientInteraction

CreditCardVerification

DAMSC Infrastructure

DAMSC - Dynamically Adaptable and Manageable Service Compositions

Goal: to support service offerings the suggested dynamic adaptation capabilities sessions (supplier-consumer associations that

remember state of the interaction; handle persistent interactions)

Infrastructure inside service components Complements works that suggest management

infrastructure outside service components

A proof-of-concept prototype - for Web Services

DAMSC - Current Status& Future Work (Part I of II)

Standardized management operations/interfaces Investigating use/extension of the Common

Information Model (CIM)

Support for service offerings includes: storage of service offerings inside service components informing consumer about active and available service

offerings storage of relationships with other service components

Support for dynamic adaptation includes: storage of relationships between service offerings storage of rules for creation of new service offerings

DAMSC - Current Status& Future Work (Part II of II)

Dynamic adaptation will be supported in sessions It should not destroy the session state

Support for sessions Standardization of session-management operations A session element stores information about a session

at the supplier side It should also contain the constraint-checking code Automatic generation of session elements (except

code!) A number of open issues remain

Relating DAMSC to other approaches for managing service components and service compositions

Some Related Work

Web Service industrial initiatives and standards; management approaches in these initiatives

Adaptation by finding alternative service components

Network/system/application/service management

Differentiated services and classes of service in telecommunications and TINA (Telecommunications Information Networking Architecture

Formal specification of constraints for software

Conclusions (Part I of II)

This research is about improving flexibility, adaptability, and agility of service compositions

The suggested capabilities complement prior works More appropriate than alternatives in some

circumstances

Main advantages: adaptation speed enhanced robustness of relationships between service

components simplicity and relatively low overhead limited complexity of required management

However, our approach has limitations

Conclusions (Part II of II)

The research has theoretical and practical relevance The overall problem has not been previously addressed Practical relevance - e.g., for compositions of e- and m-

business Web Services

Critical analyses are conducted at all research stages To determine benefits and limitations

Proof-of-concept prototypes for Web Services To check feasibility, uncover hidden issues, and

demonstrate contributions WSOL - there are already some results DAMSC - in the beginning stages of development

Questions and Answers,For More Information…

For more information… WWW site:

http://www.sce.carleton.ca/netmanage/ Contact e-mail: vladimir@sce.carleton.ca