web services core technologies

Web ServicesCore Technologies• SOA and Web Services• Web Services Standards• The XML!

• SOAP• WSDL• UDDI

Service Oriented Architecture (SOA)• SOA is an example of a the composite computing model:

“an architecture that uses distributed, discovery-based execution to expose and manage a collection of service-oriented software assets”

In this model:

• capabilities (i.e. software assets) should be dynamically discoverable• should be a clear separation of the software's capabilities and its

implementation • should be possible to quickly assemble impromptu computing

communities with minimal coordinated planning efforts, installation technicalities or human intervention.

What does this entail?

• Every step of the process needs to be machine processable• Service description• Data description• Metadata description• Service discovery• Service invocation

SOA Triad of Operations

Web Service Protocols• Web Services Protocols based

on XML• Messaging

• SOAP• Service Description

• WSDL• Service Discovery

• UDDI• Many Others

• BPEL, WSRF, WS-Addressing, WS-Security,

• WS-Notification• SOAP, WSDL are de-facto

standards• UDDI less ubiquitous – but a

good example of simple publish/find.

ServiceConsumer

ServiceProvider

ServiceRegistry

Publish(UDDI)

Find(UDDI)

Describe(WSDL)

Bind(SOAP)

SOAP

• Simple Object Access Protocol (SOAP) • Now just SOAP

• Has its roots in RPC as you can tell by the name• Envelope for exchanging XML messages• Doesn’t define message exchange pattern

• Not restricted to request/response• Doesn’t specify transport protocol

• Normally tunnelled through HTTP POST, but can be any protocol that can carry a SOAP envelope

• Structurally very similar to an (X)HTML document…

SOAP Document• Envelope

• Top-level wrapper• Header (optional)

• Security and authentication information (WS-Security)

• Routing information (WS-Addressing)

• Resource information (WSRF)• …

• Body • XML encoded application data

• Attachments (optional and used less now)• Additional non XML-data

(binary, unencoded text, etc.)

SOAP Envelope(Required)

SOAP Header(Optional)

Extension Informatione.g. routing, security

SOAP Body(Required)

Application Datae.g. request, response

error

SOAP Request (HTTP)POST /InStock HTTP/1.1Host: www.stock.orgContent-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<?xml version="1.0"?><soap:Envelope

xmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Header>... (optional header information)

</soap:Header>

<soap:Body xmlns:m="http://www.stock.org/stock"><m:GetStockPrice>

<m:StockName>IBM</m:StockName></m:GetStockPrice>

</soap:Body></soap:Envelope>

HTTPHeader

SOAPEnvelope

SOAPBody

SOAPHeader

This envelope is dependent on HTTP

SOAP Response (HTTP)HTTP/1.1 200 OKContent-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle ="http://www.w3.org/2001/12/soapencoding">

<soap:Header>... (optional header information)

</soap:Header>

<soap:Body xmlns:m ="http://www.stock.org/stock"><m:GetStockPriceResponse>

<m:Price>34.5</m:Price></m:GetStockPriceResponse>


SOAP Faults

• SOAP fault sent instead of normal response if something goes wrong<Body xmlns=http://www.w3.org/2001/12/soap-envelope>

<Fault><faultcode>Client</faultcode> <faultstring>Something went wrong</faultstring> <detail>Application specific error

information</detail></Fault>

</Body>

• Fault Code• Client – Message incorrectly formed by client• Server – Problem on server so message could not

proceed• VersionMismatch – Invalid namespace for SOAP

envelope• MustUnderstand – Header element not understood

WS-Addressing

• The previous example was dependent on HTTP to have an address• WS-Addressing overcomes this• Allows addressing information to be embedded in the SOAP

header• E.g. To, From, FaultTo

• These values can also be transferred in a SOAP body using an EndpointReference xml structure

• WS-Addressing specifies how an EndpointReference can be mapped to a bunch of SOAP headers.

WS-Addressing

<wsa:EndpointReference> <wsa:Address>http://example.com/service</wsa:Address></wsa:EndpointReference>

Simple EndpointReference:

Gets mapped to SOAP Header:

<soap:Header> <wsa:MessageID>urn:uuid:2</wsa:MessageID> <wsa:To>http://example.com/service</wsa:To> </soap:Header>

EPR Can contain other info, e.g.:ReferenceParameters – application specific keysService description location – WSDL file

CM0356/CMT606 Spring 2008

EndpointReference toSOAP Headers

EndpointReference

Address

ReferenceParameters

http://server.com

Element

Element

…

SOAP Envelope

Header

Body

To

http://server.com

Element

Element

…

SOAP Request(HTTP & WS-Addressing)

POST /StockMarketService HTTP/1.1Host: www.stock.orgContent-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<?xml version="1.0"?><soap:Envelope

xmlns:soap=http://www.w3.org/2001/12/soap-envelopexmlns:wsa="http://www.w3.org/2005/08/addressing"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Header><wsa:MessageID>urn:uuid:1</wsa:MessageID>

<wsa:ReplyTo> <wsa:Address>http://example.com/business/client</wsa:Address></wsa:ReplyTo><wsa:To>http://www.stock.org/StockMarketService</wsa:To>

<wsa:Action>http://www.stock.org/GetStockMarket</wsa:Action></soap:Header>

<soap:Body xmlns:m="http://www.stock.org/stock"><m:GetStockMarket> <m:MarketName>DOW</m:MarketName></m:GetStockMarket>


HTTPHeader

SOAPEnvelope

SOAPBody

SOAPHeader

SOAP Response(HTTP & WS-Addressing)

HTTP/1.1 200 OKContent-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<soap:Envelopexmlns:soap=http://www.w3.org/2001/12/soap-envelopexmlns:wsa="http://www.w3.org/2005/08/addressing"soap:encodingStyle ="http://www.w3.org/2001/12/soapencoding">

<soap:Header><wsa:MessageID>urn:uuid:2</wsa:MessageID><wsa:RelatesTo>urn:uuid:1</wsa:RelatesTo><wsa:To>http://example.com/business/client</wsa:To>

<wsa:Action> http://www.stock.org/GetStockMarketResponse</wsa:Action></soap:Header>

<soap:Body xmlns:m ="http://www.stock.org/stock"><m:GetStockMarketResponse> <wsa:EndpointReference> <wsa:Address>http://www.dow-service.com</wsa:Address> </wsa:EndpointReference></m:GetStockMarketResponse>


SOAP• XML based• Simple and Lightweight• Compared to CORBA, RMI, DCOM etc.

• Language and OS Independent• Unlike RMI (Java) or DCOM (Windows)

• Transport Protocol Independent• Transfer Protocol Independent with WS-Addressing

• Extensible• Additional features can be included in header

• Vendor Support• IBM, Microsoft, Apache, HP, Sun, etc

WSDL

• Web Service Definition Language (WSDL)• WSDL documents describe:• Where the service resides,

and• How to invoke the service

• Generally available as web pages• e.g. http://bouscat.cs.cf.ac.uk/someService?

WSDL• Location of WSDL relative to Web Service not

specified• Like CORBA Interface Definition Language (IDL) but

more flexible

WSDL Documents (1)• Types

• What data types will be transmitted• Messages

• What messages will be transmitted• Port Types

• What operations (functions) will be supported

• Bindings• How will the messages be transmitted

on the wire?• What message protocol (e.g. SOAP)

specific details are there?• Service

• Where is the service located?

Types

Messages

Port Types

Bindings

Service

WSDL Documents (2)

Port(http://host/)

Binding(e.g. SOAP)

Port

Binding

Port Type

Operation(s)(in) Message (out) Message

Service

Abstract Definition

• Service can have multiple ports• A port is an endpoint to which

messages are sent• e.g. http://cs.cf.ac.uk/service

• Each port is bound to:• A message protocol

• e.g. SOAP• A port type• via the binding element

• Port types specify:• Operation name• Input message type• Output message type

• Types defined using XML Schemas

WSDL Documents (3)

<message name="getBookRequest"><part name="param" element="isbn"/>

</message>

<message name="getBookResponse"><part name="resp" element="book"/>

</message>

<portType name="bookPortType"><operation name="getBook"> <input message="getBookRequest"/> <output message="getBookResponse"/></operation>

</portType>

AbstractDefinition ofService

point to xmlin the typessection

WSDL Documents (4)<binding type="bookPortType" name="bookBind">

<soap:binding style="document"transport="http://schemas.xmlsoap.org/soap/http"/>

<operation name=“getBook”> <soap:operation soapAction="getBook"/> <input> <soap:body use="literal"/> </input> <output> <soap:body use="literal"/> </output></operation>

</binding>

<service name="Hello_Service"> <port binding="bookBind" name="bookPort"> <soap:address location="http://localhost/bookservice"/> </port>

</service>

UDDI

• Universal Description, Discovery and Integration (UDDI) Protocol• Originally Microsoft, IBM and Ariba• Registry for business services• Like a phone book for Web Services, although not

actually restricted to Web Services• XML-based

• UDDI directory contains three components• White Pages - Businesses• Yellow Pages – Services provided by the

businesses• Green Pages – How these services can be

accessed

UDDI – White Pages

• Information about businesses• Name• Description of the business

• Potentially multiple languages• Contact information

• Address• Phone number• etc.

• Other information• Dun & Bradstreet Universal Numbering System number

(D.U.N.S)

UDDI Data Model (1)

<businessEntity businessKey=“ABCD”> <name>BBC</name> <description> ... </description></businessEntity>

UDDI – Yellow Pages

• Classification of services/businesses based on standard taxonomies• Standard Industrial Classification (SIC)

• 7361 = Services - Employment Agencies• 7385 = Services - Telephone Interconnect Systems

• United Nations Standard Products and Services Code (UNSPSC)• 93141800 = Employment • 83111603 = Cellular telephone services

• A business may provide multiple services

UDDI Data Model (2)


<businessService serviceKey=“EFGH” businessKey=“ABCD”> <name>News</name></businessService>

<businessService serviceKey=“IJKL” businessKey=“ABCD”> <name>Weather</name></businessService>

UDDI – Green Pages

• Information and service bindings, i.e. how a service can be accessed• Web Service related

• Web Service address• Parameters

• Non-Web Service related• E-mail• FTP• CORBA• Telephone

• A service may have multiple bindings (e.g. a Web Service binding, a telephone binding)

UDDI Data Model (3)

<bindingTemplate> bindingKey=“IJKL” serviceKey=“EFGH”> <description> Web Page </description> <accessPoint> http://news.bbc.co.uk </accessPoint></bindingTemplate>

<bindingTemplate> bindingKey=“MNOP” serviceKey=“EFGH”> <description> Web Service </description> <accessPoint> http://bbc.co.uk/news </accessPoint> <tModelInstanceDetails> <tModelInstanceInfo tModelKey=”QRST”/> </tModelInstanceDetails> </bindingTemplate>



UDDI - tModels

• No explicit link between UDDI and WSDL• Binding template contains access point (i.e. where

to contact the service)• But no information on how to interface with the

access point (such as expected data types)• tModel (Technical Model) associates an interface

description with a binding• e.g. WSDL

• Multiple bindings may refer to the same interface (tModel)• e.g. The airline industry may define a standard

ticket booking interface, multiple airlines may implement this interface

UDDI Data Model (4)

<bindingTemplate> bindingKey=“MNOP” serviceKey=“EFGH”> <description> Web Service </description> <accessPoint> http://bbc.co.uk/news </accessPoint> <tModelInstanceDetails> <tModelInstanceInfo tModelKey=”QRST”/> </tModelInstanceDetails> </businessTemplate>

<tModel tModelKey=”QRST”> <overviewDoc> <overviewURL> http://bbc.co.uk/news?wsdl </overviewURL> </overviewDoc></tModel>



UDDI Query

<find_business> <findQualifiers> <findQualifier> uddi:uddi.org:findQualifier:exactMatch </findQualifier> </findQualifiers> <name> BBC </name></find_business>

• Also find_service, find_binding, find_tModel• NOTE: This search is lexical

Putting It All Together

ServiceConsumer

ServiceProvider

ServiceRegistry

Publish(UDDI)

Find(UDDI)

Describe(WSDL)

Bind(SOAP)

<businessEntity> <name>Book Club</name> <businessService> <name>Book Service</name> <bindingTemplate> <description>Web Service</description> <tModelInstanceDetails> <tModelInstanceInfo tModelKey=”QRST”/> </tModelInstanceDetails> </bindingTemplate> <tModel tModelKey=”QRST”> <overviewDoc> <overviewURL> http://cs.cf.ac.uk/bookservice?wsdl </overviewURL> </overviewDoc> </tModel> </businessService> </businessEntity>

<find_service> <findQualifiers> <findQualifier> exactMatch </findQualifier> </findQualifiers> <name> Book Service </name></find_service>

http://cs.cf.ac.uk/bookservice


ServiceConsumer

ServiceProvider

ServiceRegistry

Publish(UDDI)

Find(UDDI)

Describe(WSDL)

Bind(SOAP) http://cs.cf.ac.uk/bookservice

<message name="getBookRequest"> <part name="param“ element="isbn"/></message><message name="getBookResponse"> <part name="resp" element="book"/></message><portType name="bookPortType"> <operation name="getBook"> <input message="getBookRequest"/> <output message="getBookResponse"/> </operation></portType><binding type="bookPortType" name="bookBind"> <soap:binding style="document" transport=http://schemas.xmlsoap.org/soap/http <operation> <soap:operation soapAction="getBook"/> <input> <soap:body use="literal"/> </input> <output> <soap:body use="literal"/> </output> </operation></binding><service name="Hello_Service"> <port binding="bookBind" name="bookPort"> <soap:address location="http://cs.cf.ac.uk/bookservice"/> </port> </service>


ServiceConsumer

ServiceProvider

ServiceRegistry

Publish(UDDI)

Find(UDDI)

Describe(WSDL)

Bind(SOAP) http://cs.cf.ac.uk/bookservice

<soap:Envelope <soap:Body> <getBookRequest> <isbn>0004702670</isbn> </getBookRequest> </soap:Body></soap:Envelope>

<soap:Envelope <soap:Body> <getBookResponse> <book> <title>Harry Potter</title> <author>J.K. Rowling</author> <date>2005-10-05</date> </book> </getBookResponse> </soap:Body></soap:Envelope>

Discussion

• What have we seen here?• A lot of XML!• What about Service Orientation? How do the

technologies support his?• SOAP as a simple, transport/transfer

independent envelope is useful.• Applications can put everything they need in it

to make messages self describing• Supports transactions/security/adressing etc.

And What About WSDL?• The abstractions defined by WSDL are Object Oriented and

encourage RPC style interactions.• Operations

• = methods• Input type/Output types

• = method parameters• Ports - collections of related operations

• = a Class/Interface• PortBinding - Instance of the Port

• = Object• This is not very service oriented! It often results in RPC

interactions simply wrapped in complex XML.

And UDDI?• The idea of UDDI is good• But it’s very complicated• Wants to cover everything• But searching is limited to lexical queries• It never really took off

• The two main public UDDI repositories run by MS and IBM have shut down

• Why?• Perhaps because of complexity• Perhaps because companies do not want to share their

commodities in this way– They want more control over how their services are

published and accessed.– Hence UDDI still works, but mainly behind the corporate

firewall - NOT on an internat scale

Conclusion

• SOA• What is it, what are its benefits?• How do core Web Service technologies support SOA?

• SOAP• Simple protocol for exchanging XML messages• Extensible via header

• WSDL• Language for defining web services

• Operations• Inputs/Outputs• Object Oriented in spirit

• UDDI• Registry for business services

• Not tied to Web Services• Complex data structures• Only supports lexical matching without extensions