Foundations And Future Directions of Web Services & Architecture

Charlton Barreto <charlton_b@acm.org>
W3C Web Services Description & Web Services Choreography Working Groups

WWW2006, Edinburgh, Scotland, 25 May 2006

Outline

Motivations for Web services
Infrastructure developed at W3C
What's ahead of us

Example of the use of Web services

Web merchant

Miscellaneous partners
- Banks
- Manufacturers
- Delivery services
Uses services from partners to conduct business with customers
Requires well-defined and easy integration with those services

What Web services are trying to achieve

Ease of integration
Extensibility
Interoperability
Machine-to-machine communication
Scalability

Lofty goals …

… translating to an architecture

… justifying some choices:

XML-based messages: for platform-independent machine processing
Framework focused on extensibility: facilitating interoperability
Machine-processable descriptions: facilitating integration
Loose coupling: maximizing scalability

Traditional Web interaction

Web services interaction

Web services stack

Stack of W3C Web services technologies

Messages

Messaging framework
Description formats
Looking to the future

Messaging framework for Web services

Built on top of Web technologies:

Messaging framework

SOAP Version 1.2

Core of the messaging framework
- XML-based
- Extensible
Defines:
- An envelope
- A processing model
- A binding framework

SOAP message

XML document
Represented abstractly as an XML Infoset

The SOAP envelope

SOAP message

SOAP message path

One-way message
Going from a sender to a receiver, possibly via intermediaries
SOAP body is targeted at the ultimate recipient
SOAP header blocks may be targeted at any participant along the message path

SOAP message path

Example of a SOAP message

<?xml version='1.0' ?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"> 
 <env:Header>
  <m:reservation xmlns:m="http://travelcompany.example.org/reservation" 
          env:role="http://www.w3.org/2003/05/soap-envelope/role/next"
          env:mustUnderstand="true">
   <m:reference>uuid:093a2da1-q345-739r-ba5d-pqff98fe8j7d</m:reference>
   <m:dateAndTime>2001-11-29T13:20:00.000-05:00</m:dateAndTime>
  </m:reservation>
 </env:Header>
 <env:Body>
  <p:itinerary
    xmlns:p="http://travelcompany.example.org/reservation/travel">
   …
  </p:itinerary>
 </env:Body>
</env:Envelope>

Message exchange patterns

One-way exchanges can be combined
Template that establishes a pattern for the exchange of messages between SOAP nodes
Examples:
- Request response
- Response: SOAP message following a non-SOAP request

Underlying protocols binding

Need to carry the XML document that a is SOAP message
Duty of a binding to an underlying protocol:
- Serialization of the Infoset (marshalling)
- Transmission
- Reconstruction of the Infoset (unmarshalling)
Can implement features:
- Message exchange pattern (MEP)
- Optimisation
- et cetera…

SOAP 1.2 HTTP Binding

Carries SOAP messages in an HTTP message
Implements 2 MEPs
- SOAP Request-Response: HTTP POST
- SOAP Response: HTTP GET
Implements the SOAP Web Method feature:
- POST
- GET
Allows for REST-style interactions

Simple addition service

public class MathService
{
    static int total=0;

    // Add an integer and return the total
    public int add(int a)
    {
        total += a;
        return total;
    }
    
    // Get the total of all the additions
    public int total()
    {
        return total;
    }
    
}

Deployed with Axis 1.3

Simple addition client

import org.apache.axis.client.Call;
import org.apache.axis.encoding.XMLType;
import org.apache.axis.soap.SOAPConstants;
import javax.xml.rpc.ParameterMode;

public class AddClient
{
   public static void main(String [] args) throws Exception {

       if (args == null || args.length != 1) {
           System.err.println("Usage: AddClient <int>");
           return;
       }
       
       Call call = new Call("http://localhost:8080/axis/MathService.jws");
       call.setSOAPVersion(SOAPConstants.SOAP12_CONSTANTS);

       Integer i = new Integer(args[0]);

       call.setOperationName("add");
       call.addParameter("a", XMLType.XSD_INT, ParameterMode.IN);
       call.setReturnType(XMLType.XSD_INT);

       Integer ret = (Integer) call.invoke(new Object [] { i });
       
       System.out.println("Added " + i + ". Current total: " + ret);
   }
}

POST example: adding a value

charlton@muramasa ~/ws-setup% java AddClient 432
Added 432. Current total: 3468

produces the following HTTP request:

POST /axis/MathService.jws HTTP/1.0
Content-Type: application/soap+xml; charset=UTF-8
Accept: application/soap+xml, application/dime, multipart/related, text/*
User-Agent: Axis/1.3
Host: 127.0.0.1:8080
Cache-Control: no-cache
Pragma: no-cache
SOAPAction: ""
Content-Length: 363

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Body>
    <add soapenv:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
      <a xsi:type="xsd:int">432</a>
    </add>
  </soapenv:Body>
</soapenv:Envelope>

resulting in the following HTTP reply:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie: JSESSIONID=16ADA5B3AB2CBE3BA1582201B4F8BC28; Path=/axis
Content-Type: application/soap+xml;charset=UTF-8
Date: Wed, 19 Oct 2005 14:34:48 GMT
Connection: close

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Body>
    <addResponse soapenv:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
      <ns1:result xmlns:ns1="http://www.w3.org/2003/05/soap-rpc">addReturn</ns1:result>
      <addReturn xsi:type="xsd:int">3468</addReturn>
    </addResponse>
  </soapenv:Body>
</soapenv:Envelope>

GET example: retrieving the total

GET /axis/MathService.jws?method=total HTTP/1.1
Host: 127.0.0.1:8080
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 Firefox/1.0.7 (Debian package 1.0.7-1)
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language: en-us,en;q=0.8,fr;q=0.6,de;q=0.4,es;q=0.2
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Cookie: JSESSIONID=9B2EB217BEA1C3EB8DEE1FE1F5E283B9

returns:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Cache-Control: no-cache
Pragma: no-cache
Content-Type: text/xml;charset=ISO-8859-1
Content-Length: 410
Date: Wed, 19 Oct 2005 14:40:30 GMT

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Body>
    <totalResponse soapenv:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
      <totalReturn xsi:type="xsd:int">3468</totalReturn>
    </totalResponse>
  </soapenv:Body>
</soapenv:Envelope>

Note about message encoding

Examples show Axis default, using SOAP encoding:

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Body>
    <totalResponse soapenv:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
      <totalReturn xsi:type="xsd:int">3468</totalReturn>
    </totalResponse>
  </soapenv:Body>
</soapenv:Envelope>

Possibility to use document style interaction:

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <soapenv:Body>
    <ns1:totalResponse xmlns:ns1="http://localhost:8080/axis/services/MathServiceDL">
      <ns1:totalReturn>3468</totalReturn>
    </ns1:totalResponse>
  </soapenv:Body>
</soapenv:Envelope>

when deployed with:

style="wrapped" use="literal"

SOAP extensibility: SOAP modules

Identified by a URI
Headers can be added to have extra processing done to the message; for example:
- Integrity checks
- Encryption
One can ensure that a header will be processed as intended:
- Optional extensions
- Mandatory extensions
  - For example, process header block in a particular order, or don't do anything

SOAP extensibility: SOAP features

Abstract functionality, such as correlation
Implemented by a module or a binding

mustUnderstand example: updated client

import org.apache.axis.client.Call;
import org.apache.axis.encoding.XMLType;
import org.apache.axis.soap.SOAPConstants;
import javax.xml.rpc.ParameterMode;
import org.apache.axis.message.SOAPHeaderElement;
import org.apache.axis.Constants;

public class AddClientMU
{
   public static void main(String [] args) throws Exception {
       
       if (args == null || args.length != 1) {
           System.err.println("Usage: AddClient <int>");
           return;
       }
       
       Call call = new Call("http://localhost:8080/axis/MathService.jws");
       call.setSOAPVersion(SOAPConstants.SOAP12_CONSTANTS);

       SOAPHeaderElement header = new SOAPHeaderElement("http://example.com/header",
                                                        "very-important-info", "blah");
       header.setMustUnderstand(true);
       header.setActor(Constants.URI_SOAP12_ULTIMATE_ROLE);


       call.addHeader(header);

       Integer i = new Integer(args[0]);

       call.setOperationName("add");
       call.addParameter("a", XMLType.XSD_INT, ParameterMode.IN);
       call.setReturnType(XMLType.XSD_INT);

       Integer ret = (Integer) call.invoke(new Object [] { i });
       
       System.out.println("Added " + i + ". Current total: " + ret);
   }
}

returns on error:

charlton@muramasa ~/ws-setup% java AddClientMU 2
Exception in thread "main" AxisFault
 faultCode: {http://www.w3.org/2003/05/soap-envelope}MustUnderstand
 faultSubcode:
 faultString: Did not understand "MustUnderstand" header(s):{http://example.com/he
ader}very-important-info
 faultActor:
 faultNode:
 faultDetail:
        {http://xml.apache.org/axis/}stackTrace:Did not understand "MustUnderstand" header(s):{http://example.com/header}very-important-info
        at org.apache.axis.message.SOAPFaultBuilder.createFault(SOAPFaultBuilder.java:222)
        at org.apache.axis.message.SOAPFaultBuilder.endElement(SOAPFaultBuilder.java:129)
        at org.apache.axis.encoding.DeserializationContext.endElement(DeserializationContext
.java:1087)
[…]

Triggering a mustUnderstand fault

POST /axis/MathService.jws HTTP/1.0
Content-Type: application/soap+xml; charset=UTF-8
Accept: application/soap+xml, application/dime, multipart/related, text/*
User-Agent: Axis/1.3
Host: 127.0.0.1:8080
Cache-Control: no-cache
Pragma: no-cache
SOAPAction: ""
Content-Length: 616

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope
   xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <soapenv:Header>
  <ns1:very-important-info
     soapenv:role="http://www.w3.org/2003/05/soap-envelope/role/ultimateReceiver"
     soapenv:mustUnderstand="true"
     xsi:type="xsd:string"
     xmlns:ns1="http://example.com/header">
      blah
  </ns1:very-important-info>
 </soapenv:Header>
 <soapenv:Body>
  <add soapenv:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
   <a xsi:type="xsd:int">2</a>
  </add>
 </soapenv:Body>
</soapenv:Envelope>

mustUnderstand fault

HTTP/1.1 500 Internal Server Error
Server: Apache-Coyote/1.1
Content-Type: application/soap+xml;charset=UTF-8
Date: Fri, 04 Nov 2005 12:38:56 GMT
Connection: close

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope
   xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <soapenv:Header>
  <soapenv:NotUnderstood qname="ns1:very-important-info"
   soapenv:role="http://schemas.xmlsoap.org/soap/actor/next"
   soapenv:mustUnderstand="false"
   xmlns:ns1="http://example.com/header"/>
 </soapenv:Header>
 <soapenv:Body>
  <soapenv:Fault>
   <soapenv:Code>
     <soapenv:Value>soapenv:MustUnderstand</soapenv:Value>
   </soapenv:Code>
   <soapenv:Reason>
    <soapenv:Text xml:lang="en">
      Did not understand &quot;MustUnderstand&quot; header(s):{http://example.com/header}very-important-info
    </soapenv:Text>
   </soapenv:Reason>
   <soapenv:Detail>
    <ns2:hostname xmlns:ns2="http://xml.apache.org/axis/">jibboom</ns2:hostname>
   </soapenv:Detail>
  </soapenv:Fault>
 </soapenv:Body>
</soapenv:Envelope>

SOAP 1.2 status

W3C Recommendation since June 2003
Basis of the messaging framework

Addressing information: Web Services Addressing 1.0

SOAP is very generic: no addressing information provided in its core capabilities
Typical interaction: HTTP request-response
Other scenarios:
- protocol without appropriate addressing capabilities
- protocol which doesn't provide correlation facilities
- send the response to an alternate location

Addressing from and to endpoints

Messages travel between endpoints
Concept of an endpoint reference (EPR):
- destination address
- reference parameters: bag of information related to an interaction
- metadata about the endpoint

Example of a EPR

<wsa:EndpointReference
     xmlns:wsa="http://www.w3.org/2005/04/addressing"
     xmlns:fabrikam="http://example.com/fabrikam"
     xmlns:wsdli="http://www.w3.org/2005/05/wsdl-instance"
     wsdli:wsdlLocation="http://example.com/fabrikam
       http://example.com/fabrikam/fabrikam.wsdl">
  <wsa:Address>
    http://example.com/fabrikam/acct
  </wsa:Address>
  <wsa:Metadata>
    <wsaw:InterfaceName>
      fabrikam:Inventory
    </wsaw:InterfaceName>
  </wsa:Metadata>
  <wsa:ReferenceParameters>
    <fabrikam:CustomerKey>
      412
    </fabrikam:CustomerKey>
  </wsa:ReferenceParameters>
</wsa:EndpointReference>

Message addressing properties

Similar to email headers
SOAP header blocks indicating source and destinations:
- wsa:From
- wsa:To
- wsa:ReplyTo
- wsa:FaultTo
Addressing metadata:
- wsa:MessageId
- wsa:RelatesTo
- wsa:Action

Example of using WS-Addressing

Web services Addressing example

Example request message

<soap:Envelope
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope"      
    xmlns:wsa="http://www.w3.org/2005/03/addressing">
  <soap:Header>
    <wsa:To>
      http://example.com/fabrikam/Purchasing
    </wsa:To>
    <wsa:Action>
      http://example.com/fabrikam/SubmitPO
    </wsa:Action>
    <wsa:MessageID>
      http://example.com/6B29FC40-CA47-1067
    </wsa:MessageID>
    <wsa:RelatesTo
        RelationshipType="http://www.w3.org/2005/03/addressing/reply">
      http://example.com/fabrikam/mid/1234
    </wsa:RelatesTo>
    <wsa:ReplyTo>
      <wsa:Address>
        mailto:client1@example.com
      </wsa:Address>
    </wsa:ReplyTo>
  </soap:Header>
  <soap:Body>
    …
  </soap:Body>
</soap:Envelope>

Example response message using `wsa:Reply-To`

<soap:Envelope
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope"      
    xmlns:wsa="http://www.w3.org/2005/03/addressing">
  <soap:Header>
    <wsa:To>
      mailto:client1@example.com
    </wsa:To>
    <wsa:Action>
      http://example.com/fabrikam/POAcceptance
    </wsa:Action>
    <wsa:From>
      <wsa:Address>
        http://example.com/fabrikam/Purchasing
      </wsa:Address>
    </wsa:From>
    <wsa:MessageID>
      mid:123@example.com
    </wsa:MessageID>
    <wsa:RelatesTo
        RelationshipType="http://www.w3.org/2005/03/addressing/reply">
      http://example.com/6B29FC40-CA47-1067
    </wsa:RelatesTo>
  </soap:Header>
  <soap:Body>
    …
  </soap:Body>
</soap:Envelope>

WS-Addressing 1.0 status

Core and SOAP binding: W3C Recommendation
Description of the extension (WSDL binding): work ongoing, covered below

Handling non-XML data

SOAP messages are XML documents
What to do with legacy binary data?
- Bitmap images (e.g. PNG)
- Other document binary formats (e.g. PDF)
Need to be part of the SOAP envelope to benefit from the SOAP processing model
Solution: include Base64-encoded data of type xs:base64Binary in the SOAP envelope

Optimizing transmission

Base64-encoding has significant processing and space overhead

Transmission issue: Transmission can be optimized
Processing issue: Base64 representation is only a logical view

XOP & MTOM

XML-binary Optimized Packaging
- An alternate serialization of the Infoset
- Optimizes serialization of binary content
SOAP Message Transmission Optimization Mechanism
- How to use XOP in SOAP

SOAP message containing binary parts

<soap:Envelope
    xmlns:soap='http://www.w3.org/2003/05/soap-envelope' 
    xmlns:xmlmime='http://www.w3.org/2004/11/xmlmime'>
  <soap:Body>
    <m:data xmlns:m='http://example.org/stuff'>
      <!-- Two binary components: a photo and a signature -->
      <m:photo>/aWKKapGGyQ=</m:photo>
      <m:sig>Faa7vROi2VQ=</m:sig>
    </m:data>
  </soap:Body>
</soap:Envelope>

SOAP message packaged with MTOM

MTOM packaging

Optimized message

MIME-Version: 1.0
Content-Type: Multipart/Related;boundary=MIME_boundary;
    type="application/xop+xml";
    start="<mymessage.xml@example.org>";
    startinfo="application/soap+xml; action=\"ProcessData\""
Content-Description: SOAP message with my pic and sig in it

--MIME_boundary
Content-Type: application/xop+xml; 
    charset=UTF-8; 
    type="application/soap+xml; action=\"ProcessData\""
Content-Transfer-Encoding: 8bit
Content-ID: <mymessage.xml@example.org>

<soap:Envelope
    xmlns:soap='http://www.w3.org/2003/05/soap-envelope'
    xmlns:xmlmime='http://www.w3.org/2004/11/xmlmime'>
  <soap:Body>
    <m:data xmlns:m='http://example.org/stuff'>
      <!-- Two binary components: a photo and a signature -->
      <m:photo><xop:Include 
    xmlns:xop='http://www.w3.org/2004/08/xop/include' 
    href='cid:http://example.org/me.jpg'/></m:photo>
      <m:sig><xop:Include 
    xmlns:xop='http://www.w3.org/2004/08/xop/include' 
    href='cid:http://example.org/my.hsh'/></m:sig>
    </m:data>
  </soap:Body>
</soap:Envelope>

--MIME_boundary
Content-Type: image/jpeg
Content-Transfer-Encoding: binary
Content-ID: <http://example.org/me.jpg>

// binary octets for JPEG image

--MIME_boundary
Content-Type: application/pkcs7-signature
Content-Transfer-Encoding: binary
Content-ID: <http://example.org/my.hsh>

// binary octets for signature

--MIME_boundary--

Resource representation SOAP header block

Associates a URI with some Base64 encoded data
Allowed to carry a representation of a Web resource
Internet media type can be expressed: Describing Media Content of Binary Data in XML
Useful for receivers that have limited connectivity

RRSHB example

<soap:Envelope
    xmlns:soap='http://www.w3.org/2003/05/soap-envelope'
    xmlns:rep='http://www.w3.org/2004/08/representation'
    xmlns:xmlmime='http://www.w3.org/2005/05/xmlmime'>
 <soap:Header>
  <rep:Representation resource='http://example.org/me.jpg'>
   <rep:Data
   xmlmime:contentType='image/jpeg'>/aWKKapGGyQ=</rep:Data>
  </rep:Representation>
 </soap:Header>
 <soap:Body>
  <x:MyData xmlns:x='http://example.org/mystuff'>
   <x:name>John Q. Public</x:name>
   <x:img src='http://example.org/me.jpg'/>
  </x:MyData>
 </soap:Body>
</soap:Envelope>

XOP/MTOM/RRSHB status

Released as a W3C Recommendation in January 2005

Doing something with this messaging framework

SOAP + WS-Addressing + MTOM allows complex exchange of rich information
Message exchange can be enhanced with added processing

But:

How does one know what messages are accepted by an endpoint?
How does one do useful things with Web services?

Description

Messaging framework
Description formats
Looking to the future

Describing Web services

Loose coupling: simple tasks are exposed as stand-alone services
In order to use those services and do useful things:
- Need to describe how to interact with a service: WSDL 2.0
- Need to describe interactions between a set of services: WS-CDL 1.0

What is WSDL 2.0?

Machine-processable language for describing Web services
Derived from WSDL 1.1
Standardized at W3C by the Web Services Description Working Group

Web service description (WSD)

WSD governing interaction between a requester agent and provider agent

"Provider agent" implements a Web service
"Requester agent" (a.k.a. "client") makes use of that Web service
WSD represents a "contract"
Specifies the message formats, transport protocols, locations

WSDL 2.0 Structure

Description document:

<description targetNamespace="…">

Message formats (schema types):

  <types> … </types>

Abstract interface of the service:

  <interface>
    <operation> … </operation>*
  </interface>

Binding of these messages to a protocol:

  <binding> … </binding>

Location of the service:

  <service>
    <endpoint> … </endpoint>*
  </service>

</description>

New Features in WSDL 2.0

Reusability: inheritance
Extensibility: MEPs, F&P
Web-friendly: safe operations, complete HTTP/1.1 support
SOAP 1.2 binding

Inheritance

An interface may inherit from one or more other interfaces:

WSD A inherits from WSD B and WSD C

Extension Mechanisms

Open content model [old]
- Can mix XML into WSDL from other namespaces
- @wsdl:required attribute tells WSDL processor whether it must be understood
Message Exchange Patterns [new]
Features and Properties [new]

Example of open content model extensibility

Specifying that WS-Addressing 1.0 must be used:

<binding name="reservationSOAPBinding" 
    interface="tns:reservationInterface"
    type="http://www.w3.org/2005/08/wsdl/soap12"
    wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">
  <wsaw:UsingAddressing wsdl:required="true" 
        xmlns:wsaw="http://www.w3.org/2005/03/addressing/wsdl"/>
  <operation ref="tns:opCheckAvailability"
      wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />
  <fault ref="tns:invalidDataFault" wsoap:code="soap:Sender" />
</binding>

Message Exchange Patterns (MEPs)

<operation> specifies logical message exchange
MEP defines a pattern of interaction between agents
- sequence
- cardinality
- direction
Base set of MEPs:
- In-Out, In-Only, Out-In, Out-Only
- Robust-In-Only, Robust-Out-Only (permit optional fault)
- Out-Optional-In, In-Optional-Out (reply is optional)
Extensible: other MEPs can also be used (identified by URI)

MEP example: In-Out

<operation name="location" wsdlx:safe="true"
           pattern="http://www.w3.org/2004/08/wsdl/in-out">
  <input element="s:location"
    style="http://www.w3.org/2005/05/wsdl/style/uri-style"/>
  <output element="s:temperature"/>
</operation>

Marking Operations as Safe

"Safe": requester agent incurs no obligation beyond invoking the operation
- Analogous to HTTP GET
- Can be implemented with SOAP 1.2 SOAP-Response MEP, or HTTP GET
Permits:
- Pre-fetch
- Re-fetch
- Safe exploration

<operation name="location" wsdlx:safe="true"
           pattern="http://www.w3.org/2005/05/wsdl/in-out">
  <input element="s:location"
    style="http://www.w3.org/2005/05/wsdl/style/uri-style"/>
  <output element="s:temperature"/>
</operation>

Bindings

Binding specifies transport protocol details
Bindings are defined for:
- SOAP 1.2
- HTTP/1.1 (including over SSL)
- SOAP 1.1 (for backward compatibility)

SOAP 1.2 Binding

Can specify use of SOAP 1.2 modules
Can describe SOAP Response MEP
Supports (new) SOAP 1.2 fault description format
Can specify underlying protocol to use (e.g. HTTP): reuse of HTTP binding mechanisms

SOAP 1.2 Binding Example

<binding name="SoapBinding" interface="m:CompleteInterface"
  type="http://www.w3.org/2005/05/wsdl/soap"
  wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP/"/>
  <!-- Use of MTOM -->
  <wsoap:module
   uri="http://www.w3.org/2004/08/soap/features/http-optimization"/>
  <operation ref="m:location"/>
  <operation ref="m:set">
    <input messageLabel="In">
      <!-- Required use of a security extension -->
      <wsoap:module required="true"
      uri="http://accurateweather.example/mySecurityExtension"/>
    </input>
    <output messageLabel="Out"/>
  </operation>
</binding>

Axis example: http://localhost:8080/axis/MathService.jws?wsdl

Only WSDL 1.1 is supported by Axis 1.3:

<?xml version="1.0" encoding="UTF-8"?>
<wsdl:definitions
    targetNamespace="http://localhost:8080/axis/services/MathServiceDL"
    xmlns:apachesoap="http://xml.apache.org/xml-soap"
    xmlns:impl="http://localhost:8080/axis/services/MathServiceDL"
    xmlns:intf="http://localhost:8080/axis/services/MathServiceDL"
    xmlns:tns1="http://doclit"
    xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
    xmlns:wsdlsoap="http://schemas.xmlsoap.org/wsdl/soap/"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<!--WSDL created by Apache Axis version: 1.3
Built on Oct 05, 2005 (05:23:37 EDT)-->
 <wsdl:types>
  <schema elementFormDefault="qualified" targetNamespace="http://doclit" xmlns="http://www.w3.org/2001/XMLSchema">
   <element name="add">
    <complexType>
     <sequence>
      <element name="in0" type="xsd:int"/>
     </sequence>
    </complexType>
   </element>
   <element name="addResponse">
    <complexType>
     <sequence>
      <element name="addReturn" type="xsd:int"/>
     </sequence>
    </complexType>
    </element>
   <element name="total">
    <complexType/>
   </element>
   <element name="totalResponse">
    <complexType>
     <sequence>
      <element name="totalReturn" type="xsd:int"/>
     </sequence>
    </complexType>
   </element>
  </schema>
 </wsdl:types>

   <wsdl:message name="totalResponse">
      <wsdl:part element="tns1:totalResponse" name="parameters"/>
   </wsdl:message>

   <wsdl:message name="totalRequest">
      <wsdl:part element="tns1:total" name="parameters"/>
   </wsdl:message>

   <wsdl:message name="addResponse">
      <wsdl:part element="tns1:addResponse" name="parameters"/>
   </wsdl:message>

   <wsdl:message name="addRequest">
      <wsdl:part element="tns1:add" name="parameters"/>
   </wsdl:message>

   <wsdl:portType name="MathServiceDL">

      <wsdl:operation name="add">
         <wsdl:input message="impl:addRequest" name="addRequest"/>
         <wsdl:output message="impl:addResponse" name="addResponse"/>
      </wsdl:operation>

      <wsdl:operation name="total">
         <wsdl:input message="impl:totalRequest" name="totalRequest"/>
         <wsdl:output message="impl:totalResponse" name="totalResponse"/>
      </wsdl:operation>
   </wsdl:portType>

   <wsdl:binding name="MathServiceDLSoapBinding" type="impl:MathServiceDL">

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

      <wsdl:operation name="add">
         <wsdlsoap:operation soapAction=""/>

         <wsdl:input name="addRequest">
            <wsdlsoap:body use="literal"/>
         </wsdl:input>
         <wsdl:output name="addResponse">
            <wsdlsoap:body use="literal"/>
         </wsdl:output>
      </wsdl:operation>

      <wsdl:operation name="total">
         <wsdlsoap:operation soapAction=""/>
         <wsdl:input name="totalRequest">
            <wsdlsoap:body use="literal"/>
         </wsdl:input>
         <wsdl:output name="totalResponse">
            <wsdlsoap:body use="literal"/>
         </wsdl:output>
      </wsdl:operation>

   </wsdl:binding>

   <wsdl:service name="MathServiceDLService">
      <wsdl:port binding="impl:MathServiceDLSoapBinding" name="MathServiceDL">
         <wsdlsoap:address location="http://localhost:8080/axis/services/MathServiceDL"/>
      </wsdl:port>
   </wsdl:service>
</wsdl:definitions>

Axis example in WSDL 2.0: heading

<?xml version="1.0" encoding="UTF-8"?>
<description
    targetNamespace="http://localhost:8080/axis/services/MathServiceDL" 
    xmlns:tns="http://localhost:8080/axis/services/MathServiceDL"
    xmlns:sns="http://doclit"
    xmlns="http://www.w3.org/2005/08/wsdl"
    xmlns:wsdlsoap="http://schemas.xmlsoap.org/wsdl/soap/"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:wsoap="http://www.w3.org/2005/08/wsdl/soap"
    xmlns:whttp="http://www.w3.org/2005/08/wsdl/http"
    xmlns:wsdlx= "http://www.w3.org/2005/08/wsdl-extensions">

Axis example in WSDL 2.0: messages

   <types>
    <xsd:schema targetNamespace="http://doclit">

      <xsd:element name="total"/>

      <xsd:element name="totalResponse">
        <xsd:complexType>     
	  <xsd:sequence>      
	    <xsd:element name="totalReturn" type="xsd:int"/>
	  </xsd:sequence>
	</xsd:complexType>
      </xsd:element>

      <xsd:element name="add">
        <xsd:complexType>
	  <xsd:sequence> 
	    <xsd:element name="a" type="xsd:int"/>
	  </xsd:sequence>
	</xsd:complexType>
      </xsd:element>
            
      <xsd:element name="addResponse">
        <xsd:complexType>
	  <xsd:sequence>      
	    <xsd:element name="addReturn" type="xsd:int"/>
	  </xsd:sequence>
	</xsd:complexType>
      </xsd:element>
            
    </xsd:schema>    
   </types>

Axis example in WSDL 2.0: interface

   <interface name="MathService">

      <operation name="add" pattern="http://www.w3.org/2005/08/wsdl/in-out"
                       style="http://www.w3.org/2005/08/wsdl/rpc">
         <input element="sns:add"/>
         <output element="sns:addResponse"/>
      </operation>

      <operation name="total" pattern="http://www.w3.org/2005/08/wsdl/in-out"
                      wsdlx:safe="true">
         <input element="sns:total"/>
         <output element="sns:totalResponse"/>
      </operation>

   </interface>

Axis example in WSDL 2.0: SOAP binding

   <binding name="MathServiceSoapBinding"
            type="http://www.w3.org/2005/08/wsdl/soap"
            wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

     <operation ref="add" wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response/"/>

     <operation ref="total" whttp:location="?method=total"
                     wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response/"/>

   </binding>

Axis example in WSDL 2.0: service

   <service name="MathServiceService"
            interface="tns:MathService">

     <endpoint binding="tns:MathServiceSoapBinding" name="MathEndpoint"
              address="http://localhost:8080/axis/services/MathServiceDL"/>
   </service>

</description>

Generating a Web service client from a WSDL document

charlton@muramasa ~/ws-setup% java org.apache.axis.wsdl.WSDL2Java \
http://localhost:8080/axis/services/MathServiceDL\?WSDL

charlton@muramasa ~/ws-setup% ls localhost/axis/services/MathServiceDL
MathServiceDL.class         MathServiceDLServiceLocator.class
MathServiceDL.java          MathServiceDLServiceLocator.java
MathServiceDLService.class  MathServiceDLSoapBindingStub.class
MathServiceDLService.java   MathServiceDLSoapBindingStub.java

Generating a Web service client from a WSDL document (continued)

import localhost.axis.services.MathServiceDL.*;

public class WSDLMathClientDL {
    public static void main(String[] args) {
             Integer i = new Integer(args[0]);

             try {
               MathServiceDLService service = new MathServiceDLServiceLocator();
               MathServiceDL endpoint = service.getMathServiceDL();
               int ret = endpoint.add(i);

               System.out.println("Added " + i + ". Current total: " + ret);
             } catch (Exception e) {
               System.err.println("Exception caught: " + e);
             }
    }
}

HTTP Binding

Far more comprehensive than in WSDL 1.1
Supports GET, POST, PUT, DELETE, as well as all other HTTP methods
Can specify:
- Input, output and fault serialization
- Transfer codings
- Authentication requirements
- Use of cookies
- Use of HTTP over TLS (https)

Also provides a URL replacement syntax:

whttp:location="http://ws.foo.example/{country}/{city}"

can be serialized as:

http://ws.foo.example/Scotland/Edinburgh

Status of WSDL 2.0

W3C Candidate Recommendation, i.e. implementation testing:
- Core language
- Predefined extensions: MEPs, SOAP 1.2 and HTTP bindings
- Primer
Updated Working Drafts:
- SOAP 1.1 binding
- RDF mapping

Web Services Choreography Description Language 1.0

What is WS-Choreography?

Peer-to-peer global model operating between loosely coupled components and systems that operate to perform a common task
Each component or system may reside on different networks and have different levels of reliability and performance
Established global behavioural contract
Used across domains of control to ensure harmony (interoperability, etc.)
Based on a formalised description of external observable behaviour across domains

What is WS-CDL?

WS-CDL is the Choreography Description Language

Language that can be used to describe collaboration protocols of cooperating [Web] Service participants in which:
- Services act as peers
- Interactions may be long-lived and stateful
A CDL-based description is a multi-participant contract that describes the common observable behaviour of the collaborating service participants

Where do WS-CDL, WSDL and SOAP fit into WS-*?

WS-CDL, WSDL + SOAP in WS-*

Motivations

IT FUD

Motivations

Order from Chaos

Using CDL

One would use CDL

To ensure interoperability of services
- Guaranteed since services must conform to a common behavioural multi-party contract specified in the CDL
To create more robust services
- They can be validated statically and at runtime against a choreography description
To reduce the cost of implementing services
- Through ensuring conformance to the expected behaviour in the CDL
- This in turn can can be used to guide and structure testing
- Reduces the overall time to deployment of a service
To formally encode agreed multi-party business protocols such as fpML, FIX, SWIFT and TWIST
- Parties can use these protocols can be assured of conformance and interoperability
- Ensures collaborative development can deliver

Using CDL

How would one use CDL?

Through a validating design/editing tool
- For example, one implemented as an Eclipse plug-in
To describe one's multi-party contract in terms of a global model rendered in CDL
Through additional CDL-based tools to generate
- Skeletal code or endpoints (Java, C#, BPEL, etc.) that ensure the service behaviour conforms to the CDL
- Test programs that generate appropriate messages based on the CDL
Use additional CDL-based tools to provide runtime verification of services
Import the necessary information types (e.g. fpML + CDL) to promote collaborative design

Using CDL

WS-CDL is a design language

For describing the technical contract to be enforced between peer participants
To generate endpoint skeletal behaviour (i.e. only the observable business logic)
To generate endpoint monitors that enforce behaviour
To generate test scripts or used in conjunction with test scripts to validate the contract

CDL components

Package
- Information - data
- Participants - service locations that implement a set of roles
- Roles - service endpoints (e.g. WSDL)
- Relationships - association between roles
- Channel types - communication channel definitions
- Choreography - the multi-party behavioural contract details

CDL components

Choreography
- Composable unit that describes the behaviour between the defined participants based on the roles they play, and the channels they use to interact
Channel instances
- Represents the communication 'pipe' established between two roles
- The channel type, associated with the instance, may permit an instance of a channel to transfer other channel instances as valid messages (i.e. channel passing)

CDL components

Interaction
- Describes a communication between two participants along a channel instance
- For example, request-response, one-way, etc.
Workunits
- Represents a grouping construct for a set of contained activities
- Can define a guard condition, to make these activities conditional
- Can express a repetition condition, to indicate whether the activities should be repeated
- Can be used for synchronisation based on the variables used in the guard condition

CDL components

Activities
- Sequence - describes a sequence of activities
- Parallel - describes a parallel set of activities
- Choice - describes a mutually exclusive set of activities
- Perform - describes an enclosed choreography to be performed
- Variable assignment - describes the assignment of variable information

CDL components

Exceptions
- A special kind of workunit associated with a choreography
- Enabled when an exception is detected
Finalizers
- Defines a set of activities
- When a 'performed' choreography completes successfully, it can enable one or more of these finalizers
- One of these finalizers can be selected by the performing choreography to complete the work associated with the 'performed' choreography (e.g. Confirm of Cancel)
- This model can be used to provide compensation, as well as support a range of coordination models

CDL structure

Example

Buyer, Seller, Credit Agency, Shipper
- Buyer barters with the Seller to get a price
- Buyer accepts a price and places an order
- Seller checks Buyer's credit worthiness
- Seller requests delivery from Shipper
- Shipper sends delivery details to Seller and Buyer
How do we write this down today?
- Bubble and stick
- Sequence diagrammes
- WS-CDL

Example - bubble and stick

Bubble & Stick

Example - bubble and stick

Bubble & Stick: Buyer/Seller

Example - bubble and stick

Bubble & Stick: Credit Check/Ship

Example - sequence diagrammes

Sequence Diagramme: Normal Collaboration

Example - sequence diagrammes

Sequence Diagramme: Bartering Collaboration

Example - sequence diagrammes

Sequence Diagramme: Credit Rejection Collaboration

Example - sequence diagrammes

Sequence Diagramme: Normal Collaboration

Example - WS-CDL

Interactions
A request-response, request, response
Typed (messages are typed)
Pairing of sends-receives between "roles"
Interactions occur on a channel

Example - some interactions

Some Interactions

Example - some interactions

Some Interactions

Interaction dependencies

To define a choreography of interactions, one must first

define roleTypes
define relationshipTypes
define informationTypes
define tokenTypes
define channelTypes

Role types

Role Types

Relationship types

Relationship Types

Information types

Information Types

Token types

Token Types

Channel types

Channel Types

Channel types

Channel Types

Choreography dependencies

Then to complete defining a choreography, one must

declare variables
declare relationshipTypes

Choreography

Interactions and ordering

Interactions and Ordering

Bartering process

Bartering Process

Bartering process

Bartering Process

Dependent workunits

Dependent WorkUnits

Dependent workunits

Dependent WorkUnits

Dependent workunits

Dependent WorkUnits

Workunits

WorkUnits

Workunits

WorkUnits

Comparison

BPEL
- Orchestration implies a centralised control mechanism
- Recursive Web service composition
- Executable language
- Requires Web services

Comparison

CDL
- Choreography has no centralised control - it is shared instead between domains
- Description language
- Does not require Web services, but it targeted to deliver over them
- CDL doesn't make a distinction betweeen BPEL or any other endpoint language

Approach

Based on simple contract-like mechanisms
- Deadlock-freedom (Kobayashi, 99, 00)
- Liveness (Kobayashi, 01; Yoshida, et al, 02)
- Security (Abadi, et al; Cardelli and Gordon; Berger, Honda, Yoshida)
- Resource management (Tofte; Kobayashi; Gordon and Dal Zillo; Yoshida, et al)
- Race-condition detection (refs)
- Extension to CCS/CSP and π-calculus (Milner)

Approach

Choreography Approach

Example - tools

Bartering process - but without variables
- WS-CDL editor
  - Tree-based editor based on structural clarity
- Testing
  - Testing a choreography by simulating messages that make up interations

WS-CDL editor: Buyer-Seller

Buyer-Seller

WS-CDL editor: Simple RFQ

Simple Request For Quote

WS-CDL editor: Good test script

Good Test Script

WS-CDL editor: Bad test script

Bad Test Script

WS-CDL editor: Good simulation

Good Simulation

WS-CDL editor: Bad simulation

Bad Simulation

Status of WS Choreography

W3C Candidate Recommendation, i.e. implementation testing
- Core language
Updated Working Draft:
- Primer

What's ahead of us

Messaging framework
Description formats
Looking to the future

Looking into the future

Additional messaging extensions
Increased description capabilities

Policies: constraints and capabilities

Heterogeneous set of extensions implemented
Requirements on facets of those
Need to find a common set of extensions used to interact
Held a workshop in October 2004

Semantics in Web service descriptions

Different levels of description:
- Service taking an integer as an argument
- Service using a ISBN number as an argument
- Service giving the availability of a book identified by an ISBN number
Semantics for a service can be:
- Implied
- Expressed in human-understandable form
- Expressed in machine-readable form
More expressive descriptions; e.g.:
- Intent of a service
- Kind of data being deal with

Semantics: setting expectations

Will greatly enhance use of services
Examples of use:
- Connect two services, ensuring that they speak the same language with same meaning
- Merge data from different sources (e.g. title & titre)
- Out of a list of 50 existing services, select only the 2 candidates that actually do what the user wants
- Automatic recovery from failure, etc.
Held a workshop in June

Internationalization

Web Services Internationalization: WS-I18N
Preferences and configuration to provide culturally sensitive or multi-lingual operations
SOAP and WSDL extensions

<env:Envelope>
 <env:Header>
  <i18n:international>
   <i18n:locale>en-US</i18n:locale>
   <i18n:preferences>
    <ldml:collation>
     <ldml:alias source="de_DE" type="phonebook"/>
    </ldml:collation>
   </i18n:preferences>
  </i18n:international>
  …
 </env:Header>
 <env:Body>
  …
 </env:Body>
</env:Envelope>

Privacy

Looked at expressing privacy statements in WSDL 2.0
Using The Platform for Privacy Preferences 1.1 (P3P1.1)
Simple proposal

    <operation
     name="OperationAddr" 
     pattern="http://www.w3.org/2003/11/wsdl/in-out"
     p3patt:p3p="http://example.com/p3p-pol1.xml">
      <input message="mytypes:addrUpdate"/>
      <output message="mytypes:updateResp"/>
    </operation>

Databinding

XML Schema Patterns for Databinding
Developing a set of XML Schema patterns and their usage
allowing developers to access the data structure in Web services and other toolkits efficiently
Also chartered to build a test suite and to address versioning in coordination with:
- W3C TAG
- Web Services Description Working Group
- XML Schema Working Group

References

W3C Web Services Activity page
- http://www.w3.org/2002/ws/
W3C XML Protocol page
- http://www.w3.org/2000/xp/Group/
W3C Web Services Description 2.0 page
- http://www.w3.org/2002/ws/desc/
W3C Web Services Choreography 1.0 page
- http://www.w3.org/2002/ws/chor/
WS-Policy page
- http://www-128.ibm.com/developerworks/library/specification/ws-polfram/
W3C Semantic Web page
- http://www.w3.org/2001/sw/
This talk: http://charltonb.typepad.com/talks/052506-cbb-www2006/
Linked from http://www.w3.org/Talks/

Foundations And Future Directions of Web Services & Architecture

Outline

Example of the use of Web services

What Web services are trying to achieve

… translating to an architecture

Traditional Web interaction

Web services interaction

Web services stack

Messages

Messaging framework for Web services

SOAP Version 1.2

SOAP message

The SOAP envelope

SOAP message path

Example of a SOAP message

Message exchange patterns

Underlying protocols binding

SOAP 1.2 HTTP Binding

Simple addition service

Simple addition client

POST example: adding a value

GET example: retrieving the total

Note about message encoding

SOAP extensibility: SOAP modules

SOAP extensibility: SOAP features

mustUnderstand example: updated client

Triggering a mustUnderstand fault

mustUnderstand fault

SOAP 1.2 status

Addressing information: Web Services Addressing 1.0

Addressing from and to endpoints

Example of a EPR

Message addressing properties

Example of using WS-Addressing

Example request message

Example response message using wsa:Reply-To

WS-Addressing 1.0 status

Handling non-XML data

Optimizing transmission

XOP & MTOM

SOAP message containing binary parts

SOAP message packaged with MTOM

Optimized message

Resource representation SOAP header block

RRSHB example

XOP/MTOM/RRSHB status

Doing something with this messaging framework

Description

Describing Web services

What is WSDL 2.0?

Web service description (WSD)

WSDL 2.0 Structure

New Features in WSDL 2.0

Inheritance

Extension Mechanisms

Example of open content model extensibility

Message Exchange Patterns (MEPs)

MEP example: In-Out

Marking Operations as Safe

Bindings

SOAP 1.2 Binding

SOAP 1.2 Binding Example

Axis example: http://localhost:8080/axis/MathService.jws?wsdl

Axis example in WSDL 2.0: heading

Axis example in WSDL 2.0: messages

Axis example in WSDL 2.0: interface

Axis example in WSDL 2.0: SOAP binding

Axis example in WSDL 2.0: service

Generating a Web service client from a WSDL document

Generating a Web service client from a WSDL document (continued)

HTTP Binding

Status of WSDL 2.0

Web Services Choreography Description Language 1.0

What is WS-CDL?

Where do WS-CDL, WSDL and SOAP fit into WS-*?

Motivations

Motivations

Using CDL

Using CDL

How would one use CDL?

Example response message using `wsa:Reply-To`