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Chapter 3

Web Services

Phil Feibish

IT 3653


From: From P2P to Web Services and Grids

Peers in a Client/Server World

Taylor, Ian J. Springer, 2005

9/13/2005

From: Taylor, 2005

2

Quote


Tim Berners
-
Lee, inventor of the World Wide Web,
noted….


“As we look forward, we are tempted to distinguish
between the multimedia world of information targeted
for human perception, and the well
-
defined world of
data which machines handle … The Web technology
must allow information intended for a human to be
effectively presented, and also allow machine
processable data to be conveyed. Only then can we
start to use computers as tools again.”

9/13/2005

From: Taylor, 2005

3

Introduction


Web historically contained data for human
consumption



Text or database info converted into HTML human
-
readable format.



Poor format for
machine
-
to
-
machine
communication



Next generation Web must handle
data
, not just
text
.



Must have links to data sources in machine
-
to
-
machine useable formats.

9/13/2005

From: Taylor, 2005

4

3.1.1 What do we need?


Machine
-
to
-
Machine Web communication



XML (a standard data format)


3 core technologies

1.
SOAP (an envelope for the XML message)

2.
WSDL (description for the interface for the
Web service)

3.
UDDI (lookup service for dynamically
locating Web services)

9/13/2005

From: Taylor, 2005

5

Figure 3.3: Web Services

9/13/2005

From: Taylor, 2005

6

XML


eXtensible Markup Language


An extremely simple dialect of SGML


Structured document of
self
-
describing data



XML

is the format used for representing and
exchanging data on the Web.

9/13/2005

From: Taylor, 2005

7

Web Services


Def: a software system designed to support
interoperable machine
-
to
-
machine interaction
over a network.



In simple terms, Web services provide the
definitions (and infrastructure) to allow
applications to exchange XML messages with
each other.

9/13/2005

From: Taylor, 2005

8

Web Services


Another Def: a distributed systems
technology that users standard Internet
protocols to move XML documents between
services processes.



Simply, Web services are software programs
that enable applications to talk to each other
remotely via XML messages.

9/13/2005

From: Taylor, 2005

9

How does it work?


A program sends a request to a remote Web
service containing an XML message and optionally
receives a response.



Although web servers are the next generation
Internet,
Web services do NOT need a Web
server to run at all!



A minimal Web service has 3 components:

1.
The service

2.
The document (XML)

3.
The address (TCP, HTTP, etc)

9/13/2005

From: Taylor, 2005

10

A minimal Web service

9/13/2005

From: Taylor, 2005

11

Web Services Architecture


Web Services are
interoperable

and
loosely
coupled.


See figure 3.6

9/13/2005

From: Taylor, 2005

12

Figure 3.6

9/13/2005

From: Taylor, 2005

13

Questions?