Based on the paper“Myths around Web Services”

by Gustavo Alonso

Web Services & Myths Around it

Debashis RoyDeepa Saha

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What is claimed?

Web service is a natural evolution of conventional middleware necessary to meet the challenges of the Web and of B2B application integration.

Author discusses the challenges and solutions that remain relevant regardless of how emerging standards and technologies evolve.

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How the claim is proved?

Web services are an accepted & dominant standard. Web services are the best way to implement conventional

applications. Web services provide a direct link between middleware

platforms of different corporations. Dynamic binding will be a common way of working with web

services. All data will be in XML.

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Outlook towards Web services

A revolutionary technologyradical change in middleware, application integration & use of

internet.

An evolutionary stepAn additional layer on top of existing middleware and EAI

platforms.

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Presentation layer

Application logic layer

Resource managementlayer

Client

Info

rmat

ion

sys

tem

1-tier architecture2-tier architecture

Application logic layer

Resource managementlayer

Client

Info

rmat

ion

sys

tem

Presentation layer

MiddlewareApplication logic layer

Resource managementlayer

Info

rmat

ion

sys

tem

Client

Presentation layer

serv

er3-tier architecture

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From Middleware to Web Services

Web Services & Myths Around it

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Middleware

Basic infrastucture behind distributed information system

Interaction between applications across heterogeneous platforms

Solution to integrating set of servers and applications under a common service interface

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DistributedSystems

MiddlewareSystems

ProgrammingLanguagesDatabases

Operating Systems

Networking

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Types of middleware

RPC based systemsTransforms procedure calls to remote procedure callsFoundation of web services middleware

TP monitorsRPC system with transactional capabilities

Object brokersRPC system with object-oriented aspect

Object monitorTP monitors with object-oriented aspect

Message-Oriented Middleware (MOM)TP monitors with persistent message queuing feature

Message brokersMOM with message filtering and transforming capability

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Enterprise Application Integration (EAI)

Extends middleware capabilities to cope with application integration

Uses application logic layers of different middleware systems as building blocks

Integrates applications and enterprise data sources so that they can easily share business processes and data

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Middleware

Middleware

MiddlewareMiddleware

EAI

Middleware

Middleware

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Web Technologies

Web browsersHTML, Java

WebServer

MiddlewareServer

Databases

Legacy Systems

….Intra-enterprise application integration

Inter-enterprise application integration

Web Technology

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Web Services

A way to expose the functionality of an information system and making it available through standard web technologies.

“a software application identified by a URI, whose interfaces and bindings are capable of being defined, described, and discovered as XML artifacts. A Web service supports direct interactions with other software agents using XML-based messages exchanged via Internet-based protocols” [W3C]

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Web Services Architecture

Web Services &

Myths Around it

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The two Facets of Web Services architecture

Internal architectureWeb services expose internal operations to be invoked

through the web Receive requests through the web Pass the requests to the underlying IT system

External architectureA middleware architecture which integrates different web

services

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Web service architecture comprises Internal and external architecture

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Clients from other

companies

Basic architecture of a Web service implemented atop a tiered architecture

Conventional

Middleware

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External architecture of Web services

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A Quick Overview of Web Services

Web Services &

Myths Around it

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Web Service Components

Web service architecture has three componentsService requesterService providerService registry

Basic infrastructure is implemented withUDDI

A name and directory server

WSDL A way to describe services

SOAP A way to communicate

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Universal Description, Discovery and Integration

A specification that defineshow to interact with a registryWhat the entries on the registry look like

Interaction with UDDIRegistration

Adding new service descriptions to the registry

Lookup Queries to search for right services

Types of UDDI registryPublic

Open search-engines for web services

Private Created by companies for their own use

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Web Services Definition Language

Defines the interface to a web service

Types XML schema describing used data types

Messages Necessary to invoke an operation of the

service

Operations Reference to input/output message

Port type Set of operations that conform an instance of a

service

Binding Actual protocol to be used to invoke the

operations

Services and ports References to actual location of service

Types

Message

Port Type Operatio

nOperation

Binding

Service

Abstract Part

Concrete Part

Port

WSDL Specification

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Simple Object Access Protocol

A specification of a protocol wrapper

Interaction between requester, provider and registry happen through SOAP

Provides a standardized way toTransform different protocols Interaction mechanisms into XML

documents

SOAP Envelope

SOAP header

Header Block

SOAP Body

Body Block

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Interaction among the Web service components

Publish

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The Myths Around Web Services

Web Services & Myths Around it

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Web services and standards

AssumptionMost applications will speak and understand XMLAll systems will support SOAPEverybody will advertise their service in UDDI registriesAll services will be described in WSDL

RealityStandards no longer means globally unique in the B2B world.

Other competing B2B standards coexist In manufacturing – Electronic Data Interchange (EDI) In financial world – Society for World-wide Interbank Financial

Telecommunication (SWIFT)

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Web services and standards….(contd.)

FactWeb services are biased towards the protocols,

representation and standards of their underlying middleware.Web services add a new layer to the complex multi-tier

architecture Translation to and from XML Tunneling of RPC through SOAP Clients embedded in web servers Alternative port types

ProblemsAddition of a new layer on top of the complex multi-tier

system Adds significant performance overhead Developing, tuning, maintaining and evolving of multi-tier systems

becomes more complex.

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Web Services in Conventional Applications

Conventional applications using web servicesFlight reservationsCar rentalHotel booking, etc.All of them are B2C but web services were created for B2B

applications.

There are some applications which can be implemented with web services but that might not be the best way

Applications that sends periodic bug reportsApplications that automatically download or install patchesSystems that use remote service to provide a functionality

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Web Services in Conventional Applications…. (contd.)

ProblemsWeb services are loosely coupled

Not suitable for atomic transactions among financial institutions

Trust Can applications trust external web services?

Semantics Web services cannot ensure that the remote application receives

understandable data.

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Direct Connectivity Across Corporate Boundaries

ClaimWeb services provide a direct link between middleware

platforms of different corporations.

ProblemThe complexities of application integration and software

design increase.

ClaimUsing RPC through SOAP is a gateway to interconnect the IT

infrastructure of different companies.

RealityRPC results in a tight integration among the components and

make them dependent on each other.

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UDDI and Dynamic Binding

Functionality UDDI registries are web services’ catalogues for humans

only. Semantic interpretation of parameters and operations Interaction between companies are regulated by contracts

Software EngineeringDynamic binding does not make sense for web services.UDDI registry cannot do any load balancing nor any

automatic redirection to a different URI in case of failure.

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All Data will be in XML

XML is a performance nightmare.Some data types does not get along well with it. In many cases application data need not to be in XML.

XML can be used for linking heterogeneous systems.

If data format is decided, then XML becomes the syntax of SOAP only.

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Conclusion

This paper intends to give a coherent picture ofWhat web services areWhat they contributeWhere they will be applied

Web services are, at the current stage, only a natural evolutionary step from conventional application

integration platforms.

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Questions? …and may be… Answers

Web Services & Myths Around it