Transcript Information System Infrastructure II

Web Services
Information Systems Infrastructure II
Chris Lau
[email protected]
(c) University of Toronto MIE456 2004
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Overview
What are they?
 Examples of web services
 Technologies associated with web
services
 Misconceptions of web services

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What are Web Services?


A collection of functions packaged together as a
single entity that is published onto network for
use by other programs*
What it is NOT:
 win32
technologies, J2EE, CORBA, CGI scripting
 all the above are based on different standards

Web services based on XML (eXtensible
Markup Language)
 standard
* Glass, G. “The Web
Services (r)evolution.”
way of representing data
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Examples of Web Services

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Microsoft Passport authentication service
Dentist appointment booking service that returns
dentist availability when given a date and time
Procurement service where supplies can be
purchased when provided with an item code and
quantity
Translation service converting English to French
Numerous other examples
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Major Web Services Technologies

3 main technologies:
 Simple Object Access Protocol (SOAP)
 standard packaging structure for XML documents over
variety of Internet protocols (e.g. SMTP, HTTP, FTP)
 Web Service Description Language (WSDL)
 XML technology describing interface of web service in a
standard way
 Universal
Description, Discover, and Integration
(UDDI)

worldwide registry of web services
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Major Web Services Technologies
(cont’d)

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Functionality as a whole greater than the sum
of its parts
Relationship between the three technologies:
Source: “Java Web Services.” Chappell, D., and Jewel, T
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Web Services Architecture
Web services can contain other web
services
 e.g. www.toronto.com portal may have a
restaurant finder as a web service

 May
access Mapquest as a web service to
retrieve directions and map
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Web Services Architecture
Source: “Java Web Services.” Chappell, D., and Jewel, T
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Web Services in a Broad
Perspective
Source: “Performance Considerations for Mobile Web Services.” M. Tian, T. Voight, T. Naumowicz, H. Ritter, J. Schiller
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Web Service Cost-Benefit Example

Dollar Rent A Car integration with
Southwest Airlines Co.
 both

companies operate different servers
Southwest customers can book flights AND rent
cars from Dollar Rent-A-Car without leaving their
site
 only
cost ~$1 / transaction, compared with $5
/ transaction through travel agent network
 savings in the millions ($$)!!!
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Benefits

Interoperability
 all
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three technologies supported by major vendors
Ubiquity
 communicate

through various protocols
Low barrier to entry
 concept
easy to understand, free toolkits to
implement web services

Industry support
 e.g.
allow Microsoft .NET web service communicate
with IBM VisualAge service
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Basic Web Service Model

3 main components
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processing of data into well-defined XML documents
XML document  the cornerstone of Web Services
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contains all information sent to service for processing
documents a web service can process defined via an XML schema
two entities in communication must have access to same
description
usually described using WSDL
address (aka port reference)  where is the service?
additional component is the envelope


a protocol used for message encapsulation
ensures XML document separated from other communication
processes
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Basic Web Service Model
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Almost all web
services use SOAP
protocol
Two elements:
 contains all
system info
 body  contains XML
document to be
processed
 header
Source: “Web Services and the Sun ONE
Developer Platform.” Ort, E.
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Misconceptions of Web Services

Web services often hyped as the latest
distributed object technology
 misconception

lead to limited acceptance
Disagreements among standards bodies,
vendors greatest threat to large-scale
success of web services
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Misconception: Web services are
just like distributed objects

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FACT: not reliable and transaction processing
not up-to-par with distributed systems
no distributed object characteristics (e.g.
CORBA):
 e.g.
objects, object references, life cycle (instantiate
to release), serialization, method interfaces, garbage
collection, etc.

do not define relationships or states between
service invocations, but rather identifies ongoing
conversations
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Misconception: Web Services are
the Internet’s RPC
RPC identifies remote procedures,
deciding which states should be provided
at invocation, includes extensive error
handling mechanisms
 FACT: web service only provide
abstraction for transferring XML
documents and for a remote service entity
to process them

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Misconception: Web Services only
use HTTP
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FACT: web services “transport agnostic”  i.e.
through any protocol
 e.g.
HTTP, TCP, UDP, SMTP, MQ-series, JMS, etc.
 most run on HTTP, since existing infrastructure
already using HTTP  high ROI
Web services can be transported across many protocols
Source: Vogels, W. “Web Services Are Not Distributed Objects”, IEEE Internet Computing.
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Misconception: Web Services need
web servers

FACT: do not require
 several
toolkits allow web-server-independent
deployment (i.e. WASP, WSE, Artix,
DocSOAP)

early web services exploited web server
application server functionality
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Misconception: Web Services are
reliable since they use TCP
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FACT: in some instances, no error notification if
deliver to remote peer
web services routing may go through many
intermediaries not using TCP
web services require end-to-end reliability:
remains to be seen
messages must be processed in order they were
sent
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Misconception: It’s Impossible to
debug web services

perceived since developer does not “own”
both ends
 cross-vendor
interoperability, WSDL versions
also issues

emerging diagnostic tools to mitigate this
 program to log traffic, perform
what if scenarios, analysis features
 SOAPscope
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Summary
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Web services based on XML, and 3
technologies: WSDL, SOAP, UDDI
Web services do NOT follow the object model as
CORBA or RMI
Web services are still unreliable, compared to
distributed systems
Web services can use large variety of protocols
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References
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Chappell, D., and Jewel, T. (2002), “Chapter 1: Welcome to Web
Services”, Java Web Services, O’Reilly Publishing.
Glass, G. “The Web Services (r)evolution.” http://www4.ibm.com/software/developer/library/ws_peer1.html
Vogels, W. “Web Services Are Not Distributed Objects”, IEEE
Internet Computing.
http://weblogs.cs.cornell.edu/AllThingsDistributed/archives/000343.h
tml
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