Web Services

1
Web Services

• CS-422

2
What are Web Services

• New breed of Web application
• self-contained
• self describing
• modular
• once published
• can be discovered
• located
• and invoked across the web
• application components

3
Web Services Platform

• Basic platform is XML and HTTP
• HTTP is ubiquitous
• could be done with RMI, Jini, CORBA or DCOM but
  they arent everywhere the way HTTP is
• middleware isnt always interoperable
• HTTP and the Web are simple
• the Web is a great information distribution
  vehicle
• the Web is a good way to tie middleware tools
  together
• HTTP wrappering has been around for a long time
• CORBA has used it forever to work through
  firewalls

4
To fill out the platform

• XML provides a metalanguage for
• SOAP (remote invocation)
• UDDI (trader, directory service)
• WSDL (expression of service characteristics)
• XLANG/XAML (transaction support)
• XKMS (XML Key management)
• XFS(Xmethods File System)

5
SOAP

• Simple Object Access Protocol
• defines a protocol for a uniform way of passing
  XML-encoded data, it also defines a way to
  perform remote procedure calls (RPCs) using HTTP
  as the underlying communication protocol
• the need for SOAP arises from the realization
  that the current middleware offerings, to be easy
  to use, need a WAN wrapper (HTTP)
• sending messages as XML can ensure
  interoperability
• middleware vendors are willing to include the
  tools for parsing and serializing XML in order to
  scale their approaches to wider networks
• SOAP is currently under the care of W3C and is
  frozen until such time that the W3C deems changes
  necessary

6
SOAP Message Embedded in HTTP Request
POST /StockQuote HTTP/1.1 Host
www.stockquoteserver.com
Content-Type text/xml charset"utf-8"
Content-Length nnnn
SOAPAction "Some-URI"
ltSOAP-ENVEnvelope
xmlnsSOAP-ENV"http//schemas.xmlsoap.org/soap/en
velope/" SOAP-ENVencodingStyle"h
ttp//schemas.xmlsoap.org/soap/encoding/"gt
ltSOAP-ENVBodygt
ltmGetLastTradePrice xmlnsm"Some-URI"gt
ltsymbolgtDISlt/symbolgt
lt/mGetLastTradePricegt
lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelope
gt
7
SOAP Message Embedded in HTTP Response
HTTP/1.1 200 OK Content-Type
text/xml charset"utf-8"
Content-Length nnnn
ltSOAP-ENVEnvelope
xmlnsSOAP-ENV"http//schemas.xmlsoap.org/soap/en
velope/" SOAP-ENVencodingStyle"h
ttp//schemas.xmlsoap.org/soap/encoding/"/gt
ltSOAP-ENVBodygt
ltmGetLastTradePriceResponse xmlnsm"Some-URI"gt
ltPricegt34.5lt/Pricegt
lt/mGetLastTradePriceResponsegt
lt/SOAP-ENVBodygt
lt/SOAP-ENVEnvelopegt
8
UDDI

• Universal Description, Discovery and Integration
  Service
• provides a mechanism for clients to dynamically
  find other web services
• similar to a CORBA trader
• think of it as a DNS service for business
  applications
• a UDDI registry has two kinds of clients
• those that want to publish a service (and its
  usage interfaces)
• those who want to obtain services of a certain
  kind and bind to them
• UDDI is layered over SOAP and assumes that
  requests and responses are UDDI objects send
  around as SOAP messages

9
UDDI Example
The following query, when placed inside the body
of the SOAP envelope, returns details on
Microsoft. ltfind_business generic"1.0"
xmlns"urnuddi-orgapi"gt
ltnamegtMicrosoftlt/namegt lt/find_businessgt
10
Returns ...
ltbusinessList generic"1.0" operator"Microsoft
Corporation" truncated"false"
xmlns"urnuddi-orgapi"gt ltbusinessInfosgt
ltbusinessInfo businessKey"0076B468-EB27-42
E5-AC09-9955CFF462A3"gt ltnamegtMicrosoft
Corporationlt/namegt ltdescription
xmllang"en"gt Empowering people through great
software - any time, any place and on
any device is Microsoft's vision. As
the worldwide leader in software for personal
and business computing, we strive to
produce innovative products and
services that meet our customer's
lt/descriptiongt ltserviceInfosgt ltserviceInfo
businessKey"0076B468-EB27-42E5-AC09-9955CFF462
A3"
serviceKey"1FFE1F71-2AF3-45FB-B788-09AF7FF151A4"gt
ltnamegtWeb services for smart
searchinglt/namegt lt/serviceInfogt ltserviceInfo
businessKey"0076B468-EB27-42E5-AC09-9955CFF4
62A3" serviceKey"8BF2F51F-8ED4-43FE-B66
5-38D8205D1333"gt ltnamegtElectronic Business
Integration Serviceslt/namegt lt/serviceInfogt . . lt/b
usinessInfogt lt/businessInfosgt lt/businessListgt
11
WSDL

• Web Services Definition Language
• provides a way for service providers to describe
  the basic format of web service requests over
  different protocols or encodings
• used to describe
• what a web service can do
• where it resides
• how to invoke it
• UDDI registries describe many aspects of web
  services including the binding details. WSDL fits
  into the subset of a UDDI service description
• WSDL provides a template for how services should
  be describes and bound by their clients

12
WSDL (more)

• WSDL defines services as collections of network
  endpoints or ports
• the abstract definition of endpoints and messages
  is separated from their concrete network
  deployment or data format bindings
• this allows reuse of abstract definitions of
  messages which are abstract definitions of the
  data exchanged and port types which are abstract
  definitions of collections of operations
• a port is defined by associating a network
  address with a reusable binding, a collection of
  ports define a service

13
WSDL Element Types

• Types - a container for data type definitions
  using some system ( like XSD)
• Messages - an abstract, typed definition of data
  being communicated
• Operations - an abstract description of an action
  supported by the service
• Port Type - an abstract set of operations
  supported by one ot more endpoints
• Binding - a concrete protocol and data format
  specification for a particular port type
• Port - a single endpoint defined as a combination
  of a binding and a network address
• Service - a collection of related endpoints

14
Sample
lt?xml version"1.0"?gt ltdefinitions
name"StockQuote"
targetNamespace"http//example.com/stockquote.wsd
l" xmlnstns"http//example.com/st
ockquote.wsdl" xmlnsxsd1"http//e
xample.com/stockquote.xsd"
xmlnssoap"http//schemas.xmlsoap.org/wsdl/soap/"
xmlns"http//schemas.xmlsoap.org/
wsdl/"gt lttypesgt ltschema targetNamespace"http//ex
ample.com/stockquote.xsd"
xmlns"http//www.w3.org/1999/XMLSchema"gt
ltelement name"TradePriceRequest"gt ltcomplexTypegt lt
allgt ltelement name"tickerSymbol"
type"string"/gt lt/allgt lt/complexTypegt lt/elementgt lt
element name"TradePrice"gt ltcomplexTypegt ltallgt ltel
ement name"price" type"float"/gt lt/allgt lt/complex
Typegt lt/elementgt lt/schemagt lt/typesgt
(cont.)
15
Sample (cont.)
ltmessage name"GetLastTradePriceInput"gt ltpart
name"body" element"xsd1TradePriceRequest"/gt lt/m
essagegt ltmessage name"GetLastTradePriceOutput"gt lt
part name"body" element"xsd1TradePrice"/gt lt/mes
sagegt ltportType name"StockQuotePortType"gt ltopera
tion name"GetLastTradePrice"gt ltinput
message"tnsGetLastTradePriceInput"/gt ltoutput
message"tnsGetLastTradePriceOutput"/gt lt/operatio
ngt lt/portTypegt ltbinding name"StockQuoteSoapBindin
g" type"tnsStockQuotePortType"gt ltsoap
binding style"document" transport"http//sche
mas.xmlsoap.org/soap/http"/gt ltoperation
name"GetLastTradePrice"gt ltsoapoperation
soapAction"http//example.com/GetLastTradePrice"/
gt ltinputgt ltsoapbody use"literal"
namespace"http//example.com/stockquote.xsd"
encodingStyle"http//schemas.xmlsoap.org/so
ap/encoding/"/gt lt/inputgt ltoutputgt ltsoapbody
use"literal" namespace"http//example.
com/stockquote.xsd" encodingStyle"http/
/schemas.xmlsoap.org/soap/encoding/"/gt lt/outputgt lt
/operationgt lt/bindinggt . .
16
XLANG

• Optional to the Web Services Platform
• Stands for eXtensible Language
• XLang is a notation for expressing the
  compensatory actions for any request that needs
  to be undone. The web services infrastructure can
  leverage XLang specifications to perform complex
  undo operations.

17
XAML

• Transaction Authority Markup Language
• provides a traditional two-phase commit
  transactional semantics over web services

18
XKMS

• XML Key Management Specification
• an effort by Microsoft and Verisign to integrate
  PKI and digital certificates (which are used for
  securing Internet transactions) with XML
  applications
• The key idea is to delegate the signature
  processing to a trust server on the Web, so that
  thin or mobile clients don't have to carry around
  the smarts to do all this themselves.
• XKMS relies on the XML Signature specification
  already being worked on by W3C and on anticipated
  work at W3C on an XML encryption specification.

19
XFS

• XMethods File System
• The XMethods filesystem service enables you to
  post and read files via a SOAP interface.
• This system enables developers to create services
  that utilize centralized, persistent data.
  Ideally, this type of filesystem can be used to
  centralize the storage of information which can
  be accessed by multiple nodes.
• For example, one could use this space to support
  automatic patch updates. XFS provides a client
  tool that integrates the XFS web service into a
  Windows Explorer shell. Windows Explorer is then
  integrated with the XML-SOAP-based file system.
• XFS is an open-source initiative by
  xmethods.com, the momentum of which is unclear.
  However, the idea is technically attractive