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Re: proposal for eliminating message

From: Sanjiva Weerawarana <sanjiva@watson.ibm.com>
Date: Mon, 20 Jan 2003 05:02:39 -0500
Message-ID: <004f01c2c06b$3c6d60b0$29060e09@lankabookwin2k>
To: "Martin Gudgin" <mgudgin@microsoft.com>, "Prasad Yendluri" <pyendluri@webMethods.com>
Cc: <www-ws-desc@w3.org>
MessageAre you referring to XSD's inability to handle co-occurence
constraints for attribtues? 

We're designing a language using XML as its syntax. We can choose
to use whatever legal syntactic constructs as seem appropriate
and comfortable to us. If such constructs cannot be XSD validated,
well, tough.

In this particular case I also prefer that we should spec out
whatever attributes for the type systems we choose to support
rather than the approach that Prasad prefers. However, I don't
see anything fundamentally wrong with his approach; its just
a different way ..

Sanjiva.
  ----- Original Message ----- 
  From: Martin Gudgin 
  To: Prasad Yendluri ; Sanjiva Weerawarana 
  Cc: www-ws-desc@w3.org 
  Sent: Monday, January 20, 2003 1:10 AM
  Subject: RE: proposal for eliminating message


  What is with this recent penchant for mangaling XML syntax with URIs? Since when has using the value of an attriute of type xs:anyURI to change the meaning of some other attribute been the way we do things? Oh, wait a minute, isn't that how XML namespaces work? The right way to do this is to define attributes for stuff we bake into our core spec ( which at the moment I think is just XML Schema ) and allow other type systems to use qualified attributes to do their thing, just as they do with part today.
   
  The same comments apply to the inteaction proposal.
   
  Gudge
    -----Original Message-----
    From: Prasad Yendluri [mailto:pyendluri@webMethods.com] 
    Sent: 18 January 2003 19:14
    To: Sanjiva Weerawarana
    Cc: www-ws-desc@w3.org
    Subject: Re: proposal for eliminating message


    This seems pretty reasonable to me.  One change I would like to recommend is, to split the typeIndicators into two separate attributes so that it is easily extensible others in future if needed. I.e. instead of having separate attribute name based the type-system (xsd/MIME etc.), have one attribute that identifies the type system and the other the value in the specific type system. 

    Instead of the  proposed syntax for type indicators are as follows:

xsdType="qname"
xsdElement="qname"
mimeType="string"
  
  
    We would have typeSystem="URI" type="value" (a string which is a QName for XSD). Do we still need to distinguish between "Type" and "Element" forms? 

    With this change,  the example could look as follows:


<portType name="ArchivalService">
   <operation name="StoreRecords">
      <input name="patient" typeSystem="<URI for xsd Type>" type="x:PatientIdentificationType"/>
      <input name="xrays" typeSystem="<URI for MIME Type>" type="image/jpg" minOccurs="0" maxOccurs="unbounded"/>
      <input name="reports" typeSystem="<URI for xsd Element>" type="y:LabReport" minOccurs="0" maxOccurs="unbounded"/>
      <output typeSystem="<URI for xsd Type>" type="anyURI"/>
      <fault  typeSystem="<URI for xsd Type>" type="z:SomethingWrong"/>
   </operation>
   ... other operations ...
</portType>

    Will this work?

    Regards, Prasad


    -------- Original Message -------- Subject:  proposal for eliminating message 
          Resent-Date:  Sat, 18 Jan 2003 11:05:52 -0500 (EST) 
          Resent-From:  www-ws-desc@w3.org 
          Date:  Sat, 18 Jan 2003 02:30:27 -0500 
          From:  "Sanjiva Weerawarana" <sanjiva@watson.ibm.com> 
          To:  <www-ws-desc@w3.org> 



Attached is an attempt at a compromise proposal for removing the
 construct.

Sanjiva.


--------------------------------------------------------------------------


      Removing Message
      Sanjiva Weerawarana, January 18, 2003

      1. Introduction
      This document proposes a mechanism for eliminating the <message> construct from WSDL. The proposed approach attempts at a compromise between the two extreme positions possible (keep message and replace with just a single complex type). 


      The proposal is written using the shortcut syntax, but can easily be re-written using the interaction patterns syntax if desired.

      2. Undertanding <message>
      The <message> construct in WSDL was created to address the requirement that messages often consist of more than one "thing" that needs to be sent. These "things" are typically related, but not logically part of one large structure. The most prevalent example is that of some request sent along with related information (documents). The related information may be sent as attachments, but that's a question of the message serialization used and not an issue at the abstract level of service description. 

      I believe that the concept of a message consiting of multiple parts is very real and very much required. However, the use of a new construct, <message>, to represent such messages have caused much grief.


      As things stand today, the <message> construct defines a message as consisting of a set of parts, where each part is typed by some type system. The immediately supported type system is XML Schema, using the attributes "type" or "element".


      3. Proposal 
      The new syntax proposal is as follows:

1 <portType name="ncname">
2    <operation name="ncname">+
3      <input [name="xsd:string"] type-indicator [cardinality-indicator]/>*
4      <output [name="xsd:string"] type-indicator [cardinality-indicator]/>*
5      <fault type-indicator/>*
6    </operation>
7 </portType>
      Lines 2-6 define an input-output or input-only operation. Operations have names and indicate zero or more things that may be sent as input (line 3), zero or more things that the service may generate in response (line 4) and zero or more fault types, one of which the service may send instead of a response (line 5). Each "thing" is typed using some type system and indicates its cardinality. Each "thing" may optionally be named so as to allow bindings to be selective about which parts go where in building a wire format. Note that at least one input or output must be specified and that the lack of any inputs indicates that the 


      How does one specify the type? WSDL 1.1 supported XML Schema types and elements and left room for other type systems. I propose WSDL 1.2 explicitly support XML Schema and the MIME type systems. The proposed syntaxes for type indicators are as follows:


xsdType="qname"
xsdElement="qname"
mimeType="string"
  
      Thus, any input, output or fault could be typed using XML Schema or MIME. Other type systems will be supported via extensibility.


      How does one specify the cardinality? One of the issues we've had with the <message> construct is that it did not allow one to specify that a part is optional, or that a part may repeat and so on. While it is not desired to re-invent XML Schema's mechanisms for indicating cardinality, it is indeed useful to be able assert some of that information. I propose we select a compromise position whereby we allow any input, output or fault to indicate its "minOccurs" and "maxOccurs" cardinality, where minOccurs and maxOccurs are defined as per XML Schema. The proposed syntax is as follows:

<(input|output|fault) [name="xsd:string"] type-indicator [minOccurs="int"] [maxOccurs="int"]/>
      As with XML Schema, the default value for minOccurs and maxOccurs will be 1 and "unbounded" is used to indicate infinity.

      4. Relationship to Interaction Patterns Proposal
      The interaction patterns proposal has been updated to reflect the impact of this proposal and is sent along with this (see interaction-patterns-jan-18-2003.html).

      5. Example
      Consider a medical records archival service. One of the operations offered could be to store a patient record as a patient is being discharged from a hospital. The information to be sent to the archival service includes the patient identification information, copies of all of the X-Ray images that were taken during the hospital stay, and copies of all laboratory reports. The service wil return an identification token to be used when requesting the data at a later time. 

      The following portType fragment illustrates how this functionality will be expressed using the proposed new syntax:


<portType name="ArchivalService">
   <operation name="StoreRecords">
      <input name="patient" xsdType="x:PatientIdentificationType"/>
      <input name="xrays" mimeType="image/jpg" minOccurs="0" maxOccurs="unbounded"/>
      <input name="reports" xsdElement="y:LabReport" minOccurs="0" maxOccurs="unbounded"/>
      <output xsdType="anyURI"/>
      <fault xsdType="z:SomethingWrong"/>
   </operation>
   ... other operations ...
</portType>
Received on Monday, 20 January 2003 05:06:07 GMT

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