How Web Services Work

7/28/2019 How Web Services Work

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Web services Definition:

Software components that can be

published, located, and run over theInternet using Extensible MarkupLanguage (XML)

Used to: Allow other applications to call

modules of code remotely with XML

Expose data in a database as XML

Send XML messages


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Extensible Markup Language (XML) Definition:

A markup language that describes data in astructured and human-readable text format

Example:Craig Duncanstudent37.3

Related to HTML, but more powerfulbecause XML can be modified and extended Has become the de facto standard for

representation of information content Has become the language of choice for

information exchange


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Web services diagram

Note: Simple Object Access Protocol (SOAP) is an XML message format


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Reasons to use Web services Applications can be built that are:

Platform-independent Distributed Secure

Web services will become the commonarchitecture for system and applicationintegration Based on open industry standards

Companies and government agencieswill be able to easily communicate withcustomers and external partners


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More reasons to use

Web services Loosely-coupled and flexible systems

are more useful than hard-wired andmonolithic ones: Example World Wide Web Service Oriented Architecture (SOA)

Companies and government agencieswill be able to access software remotely

that they or others have already built(reuse) Organizations will be able to extend the

life and value of legacy systems byexposing existing data as XML


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Even more reasons to use

Web services Developers will be able to integrate

applications: Quickly Easily Inexpensively

Software development and maintenancetime will be reduced Increase efficiency 30% Gartner

Data can be secured using industrystandard security methods: Secure Socket Layer (SSL) protocol

Public-key certificates WS-Security


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Web services issues Not a silver bullet

Web services provide plumbing betweenapplications

However, plumbing is essential Easy to write, hard to get right

Distributed and asynchronous software isthe hardest to develop and debug

However, not impossible XML is wordy

Takes up a lot of processor timeand bandwidth

However, up to a 90% compression ratio


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Web services technologies

(all based on XML)Name Abbreviation Use

Extensible MarkupLanguage

XML Language

Universal Description,Discovery, and Integration

UDDI Discovery

Web Services DescriptionLanguage WSDL Description

Simple Object AccessProtocol

SOAP Request and receivemessages


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Ordering at a restaurant diagram


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Calling a Web service diagram


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Web Service Description

Language (WSDL) Description

Web service equivalent of a menu

Uses XML to describe what the Webservice can do: Interface information (available functions)

Function data types

Function location information (URL address) Choice of application transfer protocol


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Application transfer

protocol choices Hypertext Transfer Protocol (HTTP)

Simple Mail Transfer Protocol (SMTP)

File Transfer Protocol (FTP) Blocks Extensible Exchange Protocol

(BEEP): A replacement for HTTP in critical

applications A generic application layer template

Uses XML to define the protocol syntax

Peer-to-peer (can be used client/sever)

Avoids the use of port 80


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Simple Object Access

Protocol (SOAP)Request and receive messages

Web service equivalent of an order

A Remote Procedure Call (RPC)that consists of XMLsent over HTTP

Other transport protocols can be used Similar in structure to a letter:

A message is written in XML

The message is wrapped in anXML envelope


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Sample SOAP request message

N99


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Sample SOAP response message

Brandywine Airport

West Chester, PA3347


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Development platforms Latest development environments and tools

understand Web service technologies:

Microsoft .NET platform

Java 2 Standard Edition (J2SE) platform

Programmers using .NET and Java do notneed to create or view UDDI, WSDL, orSOAP files directly

.NET developers only have to mark a functionwith a [WebMethod] attribute and it can becalled across the Internet

Java developers use the @Remote attribute


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Distributed application problems Developers writing distributed

applications need a way to provide: Security

Message integrity

Message confidentiality

Authentication

Authorization

Non-repudiation Reliability

Transactions

Etc.


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Solution: Web Services

Architecture (WSA) Set of infrastructure protocols that solve the

problems that every distributed applicationwritten with Web services faces

Allows developers to concentrate on writingsoftware

Similar to the U.S. Post Office:

You can place an addressed, stamped, and sealed

envelope in a mailbox and you dont have to worryabout anybody looking inside it or how it will get toits destination

You have the option to use additional services likecertified mail


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WSA design principles General purpose

Independent of application domain

Standards-based Uses widely accepted protocols

Federated

No central point of control, administration,or failure

Modular

Protocols can be used individually or

work together


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WSA security protocols diagram


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WS-Security The most important WSA security protocol

because the other security protocols use it

Provides message integrity: XML Signature

Uses an algorithm to create a message digest

The recipient compares the digest to the message

The digest needs to be encrypted

Security tokens (identity authentication) Username and password (needs SSL or VPN) X.509 certificate

Kerberos ticket

Provides message confidentiality: XML Encryption

Security tokens (same as above)


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More WSA protocols WS-ReliableMessaging

Allows messages to be delivered in the

presence of software and network failures WS-Addressing

Defines Web service endpoints whichallow message transmission through

gateways and firewalls WS-Routing

Allows a SOAP message to specifya virtualized path through a network


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Even more WSA protocols WS-Attachments

Allows attached files (documents,

pictures, sound, video, etc.) to besent with SOAP messages

WS-Transactions

Allows applications using more than one

Web service to coordinate changes Etc.


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Sample SOAP message with

WSA information in the header

http://ws.c3daero.com/getairportinformation

soap://c3daero.com/airports

mailto:[email protected]

uuid:84b9f5d0-33fb-4a81-b02b-5b760641c1d6

DJbchm5gK...

...

...

Documents

How Web Services Work