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Based on the paper“Myths around Web Services”
by Gustavo Alonso
Web Services & Myths Around it
Debashis RoyDeepa Saha
2
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.
3
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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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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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
12
Web Technologies
Web browsersHTML, Java
WebServer
MiddlewareServer
Databases
Legacy Systems
….Intra-enterprise application integration
Inter-enterprise application integration
Web Technology
13
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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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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Clients from other
companies
Basic architecture of a Web service implemented atop a tiered architecture
Conventional
Middleware
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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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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.