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Re: [soapbuilders] Schema question

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  • Robert van Engelen
    Hi, ... Sorry, I am primarely looking for OO representations in SOAP and I think there are some problems that need to be addressed at the protocol level. Again
    Message 1 of 23 , Apr 3, 2002
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      Hi,

      > How do C# or Java come into the picture? I though you were
      > discussing the limitations of XML Schema... not C#

      Sorry, I am primarely looking for OO representations in SOAP and I think
      there are some problems that need to be addressed at the protocol level.

      Again sorry, I want to demonstrate this with Java (no preference).

      Let's define a Test program:

      import java.io.*;
      public class Test
      { public static void doit(Base b) throws IOException
      { b.print();
      }
      public static void main(String argv[]) throws IOException
      { Derived d = new Derived();
      doit(d);
      }
      }

      With Base and Derived classes:

      import java.io.*;
      public class Base
      { String zip;
      public Base()
      { zip = new String("hello");
      }
      public void print() throws IOException
      { System.out.print(zip);
      }
      public void show() throws IOException
      { System.out.print(zip);
      }
      }

      import java.io.*;
      public class Derived extends Base
      { int zip;
      public Derived()
      { zip = 3;
      }
      public void show() throws IOException
      { System.out.print(zip);
      }
      }

      When running the Test program, it will print "hello" which is the zip of Base.

      Now suppose that we implement 'doit' as a remote method. You see that it
      expects a Base class instance but we hand it a Derived class instance.

      The implementation will either:
      1. pre-convert the Derived class instance to a Base class at the sending side
      2. post-convert the Derived class instance to a Base class instance at the
      recieving side.

      #1 has the advantage that it will limit the data but the disadvantage is that
      an upgrade to the receiving server-side (to allow derived class instances)
      requires recompilation of the client.

      #2 has the advantage that the client does not have to be recompiled when the
      service is upgraded to accept derived instances.

      I recall (if correct) that SOAP 1.1 allowed for a scenario such as #2 which
      explains the fact that accessors can be ignored (unless MU=1).

      Even when you use #1, it may get you into trouble. Consider echoing a derived
      class instance:

      import java.io.*;
      public class Test
      { public static Base echo(Base b) throws IOException
      { return b;
      }
      public static void main(String argv[]) throws IOException
      { Derived d = new Derived();
      Base b;
      b = echo(d);
      b.show()
      }
      }

      This should print '3' instead of 'hello'.

      All I am saying is that SOAP and schema's don't seem to support these simple
      OO semantics for RMI.

      gSOAP does support it (using scenario #2) and I have an echo method example
      that works just like the above example. I am afraid that this is not
      interoperable and cannot be supported by SOAP/WSDL because of schema problems.

      Are there any other SOAP implementation out there that supports the above
      echo example?

      - Robert
    • Yann Christensen
      ... while XML schemas don t seem to be able to preserve basic OO semantics? From what I understand, in SOAP 1.2 the S, O, A, and P don t stand for anything.
      Message 2 of 23 , Apr 3, 2002
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        > But don't you find it strange that the O in SOAP refers to Objects
        while XML schemas don't seem to be able to preserve basic OO semantics?

        From what I understand, in SOAP 1.2 the S, O, A, and P don't stand for
        anything.

        -----Original Message-----
        From: Robert van Engelen [mailto:engelen@...]
        Sent: Wednesday, April 03, 2002 11:07 AM
        To: soapbuilders@yahoogroups.com
        Subject: Re: [soapbuilders] Schema question


        Hi Wes,

        I see. But don't you find it strange that the O in SOAP refers to
        Objects
        while XML schemas don't seem to be able to preserve basic OO semantics?

        A restriction won't work as you pointed out because the zip field of the
        base
        is overwritten with a new definition for zip. Extension seems to be more
        natural. After all, we add new fields to a base class to get a derived
        class.

        Again, if this cannot be resolved in schemas/WSDL then SOAP will not be
        suitable for object exchange. The .NET guys must have a tremendous
        problem
        at their hands when they say that C# is competative to Java while Java
        preserves simple OO semantics while C# cannot? I would like to hear some
        more, especially from the .NET people :-)

        Wes Moulder wrote:
        >
        > ------=_NextPart_000_007B_01C1DB0D.2C1B77E0
        > Content-Type: text/plain;
        > charset="US-ASCII"
        > Content-Transfer-Encoding: 7bit
        >
        > Robert,
        > I believe it would have to be a restriction, not an extension, since
        > you're changing the behaviour of zip, and even then, I don't think
        > you're allowed to completely alter the type of data, just restrict its
        > possibilities.
        >
        > This is all from a vague understanding of xmlschema-1/ section 3.9.6,
        > though.
        > The multiple zip problem is still in effect, though; thus you wouldn't
        > have two zip entries.
        >
        > For better understanding of where I'm coming from, take it as if zip
        > were defined as ur-type, and string.
        > Now, send in two normalized strings. Which zip maps to which field?
        > <sequence> would say it's order dependant, right?
        > Where do parent elements go in terms of extension?
        >
        > You might also look in xmlschema-1 section 2.2.1, where it talks about
        > DataTypes.
        >
        > As far as OO goes, I don't think you can take an object that contains
        a
        > String, and replace it with an int, and have any assumptions still
        hold
        > up.
        > Take this for an example:
        >
        > Address{
        > String zip;
        > String city;
        > String country;
        > }
        >
        > and
        > USAddress :: Address {
        > Int zip;
        > }
        >
        > if I set the int on USAddress, and pass it into a function that looks
        > for an Address, the String would be empty/null, which isn't what
        you're
        > after.
        >
        > --Wes
        >
        >
        > -----Original Message-----
        > From: Robert van Engelen [mailto:engelen@...]
        > Sent: Wednesday, April 03, 2002 12:27 PM
        > To: soapbuilders@yahoogroups.com
        > Subject: Re: [soapbuilders] Schema question
        >
        >
        > Thanks!
        >
        > It is easy to overlook this kind of information in these long specs.
        >
        > One more question though: is the following legal?
        >
        > <complexType name="baseAddress">
        > <sequence>
        > <element name="city" type="xsd:string"/>
        > <element name="zip" type="xsd:string"/>
        > <element name="country" type="xsd:string"/>
        > </sequence>
        > </complexType>
        >
        > <complexType name="address">
        > <complexContent>
        > <extension base="tns:baseAddress">
        > <sequence>
        > <element name="zip" type="xsd:integer"/>
        > </sequence>
        > </extension>
        > </complexContent>
        > </complexType>
        >
        > If this is legal, is the resulting XML allowed to carry two zip
        elements
        > or
        > only one?
        >
        > I am asking this because:
        >
        > 1. gSOAP supports single inheritance. When communicating derived class
        > instances over SOAP also the base class members need to be present in
        > the
        > SOAP message (just like any OO implementation keeps base class
        > information
        > in the derived class instances).
        >
        > 2. The problem is that if schemas/WSDL disallows the above then SOAP
        is
        > not
        > suitable for OO! (or maybe it need to be accomplished with some
        tricks).
        >
        > - Robert
        >
        >
        >
        >
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        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
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        10.0pt;font-family:Arial;color:navy'>Robert,<o:p></o:p></span></font></p
        >
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>I believe it would have to be a
        > restriction, not an extension, since you’re changing the
        behaviour of zip,
        > and even then, I don’t think you’re allowed to completely
        alter the
        > type of data, just restrict its
        possibilities.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>This is all from a vague
        understanding of
        > xmlschema-1/ section 3.9.6, though.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>The multiple zip problem is still
        in
        > effect, though; thus you wouldn’t have two zip
        entries.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>For better understanding of where
        I’m
        > coming from, take it as if zip were defined as ur-type, and
        string.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>Now, send in two normalized
        strings.<span
        > style='mso-spacerun:yes'>  </span>Which zip maps to which field?
        > <sequence> would say it’s order dependant, right?<span
        > style='mso-spacerun:yes'>  </span><o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>Where do parent elements go in
        terms of
        > extension?<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>You might also look in
        xmlschema-1 section
        > 2.2.1, where it talks about DataTypes.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>As far as OO goes, I don’t
        think you
        > can take an object that contains a String, and replace it with an int,
        and have
        > any assumptions still hold up.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>Take this for an
        example:<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'>Address{<o:p></o:p></span></font></
        p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'><span
        style='mso-spacerun:yes'> 
        > </span>String zip;<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'><span
        style='mso-spacerun:yes'> 
        > </span>String city;<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'><span
        style='mso-spacerun:yes'> 
        > </span>String country;<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>}<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>and <o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>USAddress :: Address
        {<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'><span
        style='mso-spacerun:yes'> 
        > </span>Int zip;<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>}<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        > 10.0pt;font-family:Arial;color:navy'>if I set the int on USAddress,
        and pass it
        > into a function that looks for an Address, the String would be
        empty/null,
        > which isn’t what you’re
        after.<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'>--Wes<o:p></o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal><font size=2 color=navy face=Arial><span
        style='font-size:
        >
        10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal style='margin-left:.5in'><font size=2
        face=Tahoma><span
        > style='font-size:10.0pt;font-family:Tahoma'>-----Original
        Message-----<br>
        > <b><span style='font-weight:bold'>From:</span></b> Robert van Engelen
        > [mailto:engelen@...] <br>
        > <b><span style='font-weight:bold'>Sent:</span></b>
        </span></font><st1:date
        > Month="4" Day="3" Year="2002"><font size=2 face=Tahoma><span
        style='font-size:
        > 10.0pt;font-family:Tahoma'>Wednesday, April 03,
        2002</span></font></st1:date><font
        > size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
        </span></font><st1:time
        > Hour="12" Minute="27"><font size=2 face=Tahoma><span
        style='font-size:10.0pt;
        > font-family:Tahoma'>12:27 PM</span></font></st1:time><font size=2
        face=Tahoma><span
        > style='font-size:10.0pt;font-family:Tahoma'><br>
        > <b><span style='font-weight:bold'>To:</span></b>
        soapbuilders@yahoogroups.com<br>
        > <b><span style='font-weight:bold'>Subject:</span></b> Re:
        [soapbuilders] Schema
        > question</span></font></p>
        >
        > <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times
        New Roman"><span
        > style='font-size:12.0pt'><o:p> </o:p></span></font></p>
        >
        > <p class=MsoNormal style='margin-left:.5in'><font size=2 face="Courier
        New"><span
        > style='font-size:10.0pt;font-family:"Courier New"'><br>
        > <tt><font face="Courier New">Thanks!</font></tt><br>
        > <br>
        > <tt><font face="Courier New">It is easy to overlook this kind of
        information in
        > these long specs.</font></tt><br>
        > <br>
        > <tt><font face="Courier New">One more question though: is the
        following legal?</font></tt><br>
        > <br>
        > <tt><font face="Courier New"><complexType
        name="baseAddress"></font></tt><br>
        > <tt><font face="Courier New">  <sequence></font></tt><br>
        > <tt><font face="Courier New">    <element
        > name="city" type="xsd:string"/></font></tt><br>
        > <tt><font face="Courier New">    <element
        > name="zip" type="xsd:string"/></font></tt><br>
        > <tt><font face="Courier New">    <element
        > name="country"
        type="xsd:string"/></font></tt><br>
        > <tt><font face="Courier New">  </sequence></font></tt><br>
        > <tt><font face="Courier New"></complexType></font></tt><br>
        > <br>
        > <tt><font face="Courier New"><complexType
        name="address"></font></tt><br>
        > <tt><font face="Courier New"> 
        <complexContent></font></tt><br>
        > <tt><font face="Courier New">    <extension
        > base="tns:baseAddress"></font></tt><br>
        > <tt><font face="Courier New">     
        <sequence></font></tt><br>
        > <tt><font face="Courier
        New">       
        > <element name="zip"
        type="xsd:integer"/></font></tt><br>
        > <tt><font face="Courier New">     
        </sequence></font></tt><br>
        > <tt><font face="Courier New">   
        </extension></font></tt><br>
        > <tt><font face="Courier New"> 
        </complexContent></font></tt><br>
        > <tt><font face="Courier New"></complexType></font></tt><br>
        > <br>
        > <tt><font face="Courier New">If this is legal, is the resulting XML
        allowed to
        > carry two zip elements or</font></tt><br>
        > <tt><font face="Courier New">only one?</font></tt><br>
        > <br>
        > <tt><font face="Courier New">I am asking this because:</font></tt><br>
        > <br>
        > <tt><font face="Courier New">1. gSOAP supports single inheritance.
        When
        > communicating derived class</font></tt><br>
        > <tt><font face="Courier New">instances over SOAP also the base class
        members
        > need to be present in the</font></tt><br>
        > <tt><font face="Courier New">SOAP message (just like any OO
        implementation
        > keeps base class information</font></tt><br>
        > <tt><font face="Courier New">in the derived class
        instances).</font></tt><br>
        > <br>
        > <tt><font face="Courier New">2. The problem is that if schemas/WSDL
        disallows
        > the above then SOAP is not</font></tt><br>
        > <tt><font face="Courier New">suitable for OO! (or maybe it need to be
        > accomplished with some tricks).</font></tt><br>
        > <br>
        > <tt><font face="Courier New">- Robert</font></tt><br>
        > </span></font><br style='mso-special-character:line-break'>
        > <![if !supportLineBreakNewLine]><br
        style='mso-special-character:line-break'>
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        --
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        Florida State University, 206 J. Love Bldg., Tallahassee,
        FL32306-4530
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      • Rich Salz
        The SOAP RPC encoding can send data (e.g., aliased pointers via href/id) that cannot be expressed in XML Schema. There is no requirement that WSDL use XML
        Message 3 of 23 , Apr 3, 2002
        • 0 Attachment
          The SOAP RPC encoding can send data (e.g., aliased pointers via href/id)
          that cannot be expressed in XML Schema. There is no requirement that
          WSDL use XML Schema, although it is the "preferred" (er, sorry,
          "canonical") data description.

          You could, e.g., define your own "types" extgension element that
          contained a URL to a Java interface, a Corba IDL file, etc.

          It would seem that since you want to use SOAP for things that cannot be
          expressed in XML Schema, then you shouldn't use XML Schema, and you
          needn't. :)
          /R$
        • Martin Gudgin
          No, for the same reason. The effective type definition for address is;
          Message 4 of 23 , Apr 3, 2002
          • 0 Attachment
            No, for the same reason. The effective type definition for address is;

            <complexType name="address">
            <sequence>
            <element name="city" type="xsd:string"/>
            <element name="zip" type="xsd:string"/>
            <element name="country" type="xsd:string"/>
            <element name="zip" type="xsd:integer"/>
            </sequence>
            </complexType>

            Martin


            ----- Original Message -----
            From: "Robert van Engelen" <engelen@...>
            To: <soapbuilders@yahoogroups.com>
            Sent: Wednesday, April 03, 2002 7:27 PM
            Subject: Re: [soapbuilders] Schema question


            >
            > Thanks!
            >
            > It is easy to overlook this kind of information in these long specs.
            >
            > One more question though: is the following legal?
            >
            > <complexType name="baseAddress">
            > <sequence>
            > <element name="city" type="xsd:string"/>
            > <element name="zip" type="xsd:string"/>
            > <element name="country" type="xsd:string"/>
            > </sequence>
            > </complexType>
            >
            > <complexType name="address">
            > <complexContent>
            > <extension base="tns:baseAddress">
            > <sequence>
            > <element name="zip" type="xsd:integer"/>
            > </sequence>
            > </extension>
            > </complexContent>
            > </complexType>
            >
            > If this is legal, is the resulting XML allowed to carry two zip elements
            or
            > only one?
            >
            > I am asking this because:
            >
            > 1. gSOAP supports single inheritance. When communicating derived class
            > instances over SOAP also the base class members need to be present in the
            > SOAP message (just like any OO implementation keeps base class information
            > in the derived class instances).
            >
            > 2. The problem is that if schemas/WSDL disallows the above then SOAP is
            not
            > suitable for OO! (or maybe it need to be accomplished with some tricks).
            >
            > - Robert
            >
            >
            > -----------------------------------------------------------------
            > This group is a forum for builders of SOAP implementations to discuss
            implementation and interoperability issues. Please stay on-topic.
            >
            > To unsubscribe from this group, send an email to:
            > soapbuilders-unsubscribe@yahoogroups.com
            >
            >
            >
            > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
            >
            >
          • Rosimildo daSIlva
            ... I agree. The programming languages are what they are. C#, Java, C++ and others have the constructs to build Classes, Inheritance, Polymorphism, etc.These
            Message 5 of 23 , Apr 3, 2002
            • 0 Attachment
              >
              > How do C# or Java come into the picture? I though
              > you were
              > discussing the limitations of XML Schema... not C#
              >

              I agree. The programming languages are what they are.
              C#, Java, C++
              and others have the constructs to build Classes,
              Inheritance, Polymorphism, etc.These mechanisms are
              very powerful.

              At the same time, I understand where Robert is
              coming from.

              As has been debated before, XML-Schema and in some
              extent SOAP/WSDL, are
              very limited regarding modeling of systems using
              techniques sich as Object
              Orientation. The Schema limits you on how you define
              "Messages" to be delivered
              back and forth, and WSDL is very weak regarding
              composition of end-points.

              Assuming that one "portType", defines one interface.
              It would be nice
              to compose more complex interfaces ( portTypes ) using
              inheritance:

              interface SuperTV extends PublicTV, CableTV, DishTV
              {


              };

              where: PublicTV --- described by public_tv.wsdl,
              CableTV --- described by cable_tv.wsdl,
              DiskTV --- described by dish_tv.wsdl

              Now this service, super_tv.wsdl is higher level
              service that using composition
              provide a more sophisticated service that wants
              simplicity for a fee. <g>

              This is very basic, and still missing in WSDL/SOAP.
              Imagine things
              like Security, Session Managment, QoS, etc.

              Rosimildo.



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            • david_cleary
              ... Since I haven t seen a reply that tells you how to code this, here it goes. Use a union type. Here is the syntax using an anonyomous type decl and requires
              Message 6 of 23 , Apr 4, 2002
              • 0 Attachment
                --- In soapbuilders@y..., Robert van Engelen <engelen@a...> wrote:
                >
                > Hi,
                >
                > I have a question with regard to the validity of the following
                schema:
                >
                > <complexType name="address">
                > <sequence>
                > <element name="city" type="xsd:string"/>
                > <element name="zip" type="xsd:string"/>
                > <element name="zip" type="xsd:integer"/>
                > <element name="country" type="xsd:string"/>
                > </sequence>
                > </complexType>

                Since I haven't seen a reply that tells you how to code this, here it
                goes. Use a union type. Here is the syntax using an anonyomous type
                decl and requires both to be present.

                <xs:element name="zip" minOccurs="2" maxOccurs="2">
                <xs:simpleType>
                <xs:union memberTypes="xs:int xs:string"/>
                </xs:simpleType>
                </xs:element>

                You need to use xsi:type in the instance if the datatype can't be
                determined by the data.

                David Cleary
                Progress Software
              • Noah Mendelsohn/Cambridge/IBM
                ... No, but the reason is either subtle (or pretty) as you prefer. Gudge has already pointed out that [1]: When two or more particles contained directly or
                Message 7 of 23 , Apr 4, 2002
                • 0 Attachment
                  Rob van Engelen asks:

                  >> One more question though: is the following legal?

                  >> <complexType name="baseAddress">
                  >> <sequence>
                  >> <element name="city" type="xsd:string"/>
                  >> <element name="zip" type="xsd:string"/>
                  >> <element name="country" type="xsd:string"/>
                  >> </sequence>
                  >> </complexType>
                  >>
                  >> <complexType name="address">
                  >> <complexContent>
                  >> <extension base="tns:baseAddress">
                  >> <sequence>
                  >> <element name="zip" type="xsd:integer"/>
                  >> </sequence>
                  >> </extension>
                  >> </complexContent>
                  >> </complexType>

                  No, but the reason is either subtle (or pretty) as you prefer. Gudge has
                  already pointed out that [1]:

                  'When two or more particles contained directly or indirectly in the
                  {particles} of a model group have identically named element declarations
                  as
                  their {term}, the type definitions of those declarations must be the
                  same.'

                  If you read [2] you will find out that when <extension> is used in a
                  schema document, the derived type has a {term} (essentially a particle)
                  which is the net content model. In your case, a sequence of city,zip,
                  country, zip (actually, I think it's
                  sequence(sequence(city,zip,country),zip)). This model group violates the
                  rule cited by Gudge. Hence, invalid.

                  Actually, if you are a real schema guru, you will note that this only
                  covers the common case in which you used the <schema> syntax to declare
                  your schema. The general case is covered at [3], combined with [1]. It
                  states:

                  "[Definition:] For a particle (call it E, for extension) to be a valid
                  extension of another particle (call it B, for base) one of the following
                  must be true:
                  1 They are the same particle.
                  2 E's {min occurs}={max occurs}=1 and its {term} is a sequence group whose
                  {particles}' first member is a particle all of whose properties,
                  recursively, are identical to those of B, with the exception of
                  {annotation} properties. "

                  In other words, the constructs from the base type appear in the same
                  particle of as the derived, and hence are subject to the rule cited by
                  Gudge.

                  In short, this example is clearly invalid, IMO at least.

                  [1] http://www.w3.org/TR/xmlschema-1/#Model_Group_details
                  [2] http://www.w3.org/TR/xmlschema-1/#declare-type
                  [3] http://www.w3.org/TR/xmlschema-1/#cos-particle-extend

                  ------------------------------------------------------------------
                  Noah Mendelsohn Voice: 1-617-693-4036
                  IBM Corporation Fax: 1-617-693-8676
                  One Rogers Street
                  Cambridge, MA 02142
                  ------------------------------------------------------------------







                  Robert van Engelen <engelen@...>
                  04/03/02 01:27 PM
                  Please respond to soapbuilders


                  To: soapbuilders@yahoogroups.com
                  cc: (bcc: Noah Mendelsohn/Cambridge/IBM)
                  Subject: Re: [soapbuilders] Schema question


                  Thanks!

                  It is easy to overlook this kind of information in these long specs.

                  One more question though: is the following legal?

                  <complexType name="baseAddress">
                  <sequence>
                  <element name="city" type="xsd:string"/>
                  <element name="zip" type="xsd:string"/>
                  <element name="country" type="xsd:string"/>
                  </sequence>
                  </complexType>

                  <complexType name="address">
                  <complexContent>
                  <extension base="tns:baseAddress">
                  <sequence>
                  <element name="zip" type="xsd:integer"/>
                  </sequence>
                  </extension>
                  </complexContent>
                  </complexType>

                  If this is legal, is the resulting XML allowed to carry two zip elements
                  or
                  only one?

                  I am asking this because:

                  1. gSOAP supports single inheritance. When communicating derived class
                  instances over SOAP also the base class members need to be present in the
                  SOAP message (just like any OO implementation keeps base class information
                  in the derived class instances).

                  2. The problem is that if schemas/WSDL disallows the above then SOAP is
                  not
                  suitable for OO! (or maybe it need to be accomplished with some tricks).

                  - Robert


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                • Rosimildo daSIlva
                  ... I am glad that there are people around here with that qualifications. Everytime I get close to the XML Schema spec, I feel sorry for myself, and I feel
                  Message 8 of 23 , Apr 4, 2002
                  • 0 Attachment
                    <noah_mendelsohn@...> wrote:
                    > Rob van Engelen asks:
                    >
                    > Actually, if you are a real schema guru, you will
                    > note that this only
                    > covers the common case in which you used the
                    > <schema> syntax to declare
                    > your schema. The general case is covered at [3],
                    > combined with [1]. It
                    > states:
                    >

                    I am glad that there are people around here with that
                    qualifications. <g>

                    Everytime I get close to the XML Schema spec, I feel
                    sorry for myself, and I feel so "small" thinking to
                    myself that I need the next 10 years to really
                    understand it.

                    Rosimildo.



                    __________________________________________________
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                    Yahoo! Tax Center - online filing with TurboTax
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                  • Robert van Engelen
                    Noah, Thanks. Your comments are highly appreciated. Based on this I can conclude that the extension mechanism is not suitable to implement the usual OO base
                    Message 9 of 23 , Apr 4, 2002
                    • 0 Attachment
                      Noah,

                      Thanks. Your comments are highly appreciated.

                      Based on this I can conclude that the extension mechanism is not suitable
                      to implement the usual OO base class overriding semantics. Which means that
                      a derived class (in the OO sense) must be represented with a schema
                      that is separate from the base class schema. E.g. to represent the base
                      class zip with the derived class zip I have to use a <union>. The unfortunate
                      consequence is that the base class <-> derived class information is completely
                      lost in the process and can't be retained in a WSDL document. One can argue
                      that the OO hierarchies have nothing in common with XML schemas. However,
                      since SOAP utilizes WSDL for declaring the necessary data types for RPC,
                      the OO hierarchy may be exploited by SOAP-enabled applications that have to
                      deal with object exchange. It appears that the two cannot be mixed, which is
                      unfortunate for SOAP. For example, when I declare a remote procedure in WSDL
                      with a parameter of a base type, then the procedure can never accept a derived
                      type (with additional elements) because of validation violations. A solution
                      is to write overloaded procedure definitions, one for each class. Is that a
                      recommended solution?

                      Question: Can <union> be used to refer to any schema type or only to primitive
                      schema types?

                      - Robert
                    • graham glass
                      hi robert, there is another way to look at this which i think is more useful. you *can* pass a derived schema type to a method which accepts a base schema type
                      Message 10 of 23 , Apr 4, 2002
                      • 0 Attachment
                        hi robert,
                         
                        there is another way to look at this which i think is more useful.
                         
                        you *can* pass a derived schema type to a method which accepts
                        a base schema type as long as the derived type doesn't contain
                        a field name which is a duplicate of the base name.
                         
                        i bet that 99% of the derived classes don't contain field names
                        that override those of their base classes, so this approach (with
                        a noted restriction) seems pragmatic.
                         
                        this is the kind of functionality that GLUE and many other SOAP
                        platforms support.
                         
                        cheers,
                        graham
                        -----Original Message-----
                        From: Robert van Engelen [mailto:engelen@...]
                        Sent: Thursday, April 04, 2002 4:31 PM
                        To: soapbuilders@yahoogroups.com
                        Subject: Re: [soapbuilders] Schema question


                        Noah,

                        Thanks. Your comments are highly appreciated.

                        Based on this I can conclude that the extension mechanism is not suitable
                        to implement the usual OO base class overriding semantics. Which means that
                        a derived class (in the OO sense) must be represented with a schema
                        that is separate from the base class schema. E.g. to represent the base
                        class zip with the derived class zip I have to use a <union>. The unfortunate
                        consequence is that the base class <-> derived class information is completely
                        lost in the process and can't be retained in a WSDL document. One can argue
                        that the OO hierarchies have nothing in common with XML schemas. However,
                        since SOAP utilizes WSDL for declaring the necessary data types for RPC,
                        the OO hierarchy may be exploited by SOAP-enabled applications that have to
                        deal with object exchange. It appears that the two cannot be mixed, which is
                        unfortunate for SOAP. For example, when I declare a remote procedure in WSDL
                        with a parameter of a base type, then the procedure can never accept a derived
                        type (with additional elements) because of validation violations. A solution
                        is to write overloaded procedure definitions, one for each class. Is that a
                        recommended solution?

                        Question: Can <union> be used to refer to any schema type or only to primitive
                        schema types?

                        - Robert


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                      • Noah Mendelsohn/Cambridge/IBM
                        Exactly the answer I would have given. Schema s type system is at best an 80/20 as a basis for representing this or that existing object system. First of all,
                        Message 11 of 23 , Apr 5, 2002
                        • 0 Attachment
                          Exactly the answer I would have given. Schema's type system is at best an
                          80/20 as a basis for representing this or that existing object system.
                          First of all, most programming languages emphasize inheritance of methods
                          rather than data (though there is no-doubt data inheritance going on as
                          well, but in many uses of OO only the methods are made public or protected
                          and are thus part of the overt interface contract.) Anyway, another
                          glaring hole is that schema makes no attempt at multiple inheritance (a
                          conscious keep it simple compromise.) Covering redefinition of a
                          like-named member property is probably below multiple-inheritance in terms
                          of the number of users who have screamed that they can't effectively
                          mapped to our system.

                          ------------------------------------------------------------------
                          Noah Mendelsohn Voice: 1-617-693-4036
                          IBM Corporation Fax: 1-617-693-8676
                          One Rogers Street
                          Cambridge, MA 02142
                          ------------------------------------------------------------------







                          "graham glass" <graham@...>
                          04/05/02 02:33 AM
                          Please respond to soapbuilders


                          To: <soapbuilders@yahoogroups.com>
                          cc: (bcc: Noah Mendelsohn/Cambridge/IBM)
                          Subject: RE: [soapbuilders] Schema question

                          hi robert,

                          there is another way to look at this which i think is more useful.

                          you *can* pass a derived schema type to a method which accepts
                          a base schema type as long as the derived type doesn't contain
                          a field name which is a duplicate of the base name.

                          i bet that 99% of the derived classes don't contain field names
                          that override those of their base classes, so this approach (with
                          a noted restriction) seems pragmatic.

                          this is the kind of functionality that GLUE and many other SOAP
                          platforms support.

                          cheers,
                          graham
                          -----Original Message-----
                          From: Robert van Engelen [mailto:engelen@...]
                          Sent: Thursday, April 04, 2002 4:31 PM
                          To: soapbuilders@yahoogroups.com
                          Subject: Re: [soapbuilders] Schema question


                          Noah,

                          Thanks. Your comments are highly appreciated.

                          Based on this I can conclude that the extension mechanism is not suitable
                          to implement the usual OO base class overriding semantics. Which means
                          that
                          a derived class (in the OO sense) must be represented with a schema
                          that is separate from the base class schema. E.g. to represent the base
                          class zip with the derived class zip I have to use a <union>. The
                          unfortunate
                          consequence is that the base class <-> derived class information is
                          completely
                          lost in the process and can't be retained in a WSDL document. One can
                          argue
                          that the OO hierarchies have nothing in common with XML schemas. However,
                          since SOAP utilizes WSDL for declaring the necessary data types for RPC,
                          the OO hierarchy may be exploited by SOAP-enabled applications that have
                          to
                          deal with object exchange. It appears that the two cannot be mixed, which
                          is
                          unfortunate for SOAP. For example, when I declare a remote procedure in
                          WSDL
                          with a parameter of a base type, then the procedure can never accept a
                          derived
                          type (with additional elements) because of validation violations. A
                          solution
                          is to write overloaded procedure definitions, one for each class. Is that
                          a
                          recommended solution?

                          Question: Can <union> be used to refer to any schema type or only to
                          primitive
                          schema types?

                          - Robert


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                          implementation and interoperability issues. Please stay on-topic.

                          To unsubscribe from this group, send an email to:
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                        • Robert van Engelen
                          Noah and Graham, Thanks! Please allow me to elaborate on this a little further for sake of clarity and usefulness to the SOAP interop community after which (I
                          Message 12 of 23 , Apr 5, 2002
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                            Noah and Graham,

                            Thanks!

                            Please allow me to elaborate on this a little further for sake of clarity
                            and usefulness to the SOAP interop community after which (I hope) this
                            issue can be closed.

                            gSOAP does support single inheritance and allows a derived class to be passed
                            to a method that accepts a base class.

                            However, to generate valid WSDL schemas for the 1% of code that does in fact
                            override base class fields needs some tweaking by renaming derived class fields
                            (in the language domain) to unique element names (in the schema domain).
                            I was just concerned that this renaming might break interoperability
                            between OO-based SOAP implementations (whatever that means) and I am very
                            interested to hear how other SOAP implementations handle this. [Note that gSOAP
                            has a fully automatic mapping from C/C++ data types to SOAP data types.]

                            As a general solution, a field 'F' of a derived class 'D' can be renamed to an
                            element '<D.F>' in case 'F' is a field in a base class. Any WSDL importer will
                            just use this (unique) element and doesn't need to be concerned about
                            overriding issues.

                            When gSOAP would import such as schema though, gSOAP could in fact declare a
                            derived class with field 'F' to recreate the (language-specific) OO hierarchy
                            with member overriding.

                            Interestingly enough, this approach allows for both OO implementations and
                            non-OO implementations to cope with schemas derived by extension. Maybe
                            I am reinventing the wheel here?

                            - Cheers, Robert
                          • Noah Mendelsohn/Cambridge/IBM
                            Thanks. I would have thought there were other potential member name issues. For example, if your programming language allows variable names to have
                            Message 13 of 23 , Apr 5, 2002
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                              Thanks. I would have thought there were other potential member name
                              issues. For example, if your programming language allows variable names
                              to have characters that are not XML Name characters. In general, I would
                              expect that for real interop of some particular inheritance model, someone
                              would have to write a specification saying: "here's how we map member
                              names that aren't legal XML names, here is how we rename members in the
                              1% of cases where a derived class does an incompatible override of a base,
                              etc."

                              ------------------------------------------------------------------
                              Noah Mendelsohn Voice: 1-617-693-4036
                              IBM Corporation Fax: 1-617-693-8676
                              One Rogers Street
                              Cambridge, MA 02142
                              ------------------------------------------------------------------







                              Robert van Engelen <engelen@...>
                              04/05/02 11:40 AM
                              Please respond to soapbuilders


                              To: soapbuilders@yahoogroups.com
                              cc: (bcc: Noah Mendelsohn/Cambridge/IBM)
                              Subject: Re: [soapbuilders] Schema question


                              Noah and Graham,

                              Thanks!

                              Please allow me to elaborate on this a little further for sake of clarity
                              and usefulness to the SOAP interop community after which (I hope) this
                              issue can be closed.

                              gSOAP does support single inheritance and allows a derived class to be
                              passed
                              to a method that accepts a base class.

                              However, to generate valid WSDL schemas for the 1% of code that does in
                              fact
                              override base class fields needs some tweaking by renaming derived class
                              fields
                              (in the language domain) to unique element names (in the schema domain).
                              I was just concerned that this renaming might break interoperability
                              between OO-based SOAP implementations (whatever that means) and I am very
                              interested to hear how other SOAP implementations handle this. [Note that
                              gSOAP
                              has a fully automatic mapping from C/C++ data types to SOAP data types.]

                              As a general solution, a field 'F' of a derived class 'D' can be renamed
                              to an
                              element '<D.F>' in case 'F' is a field in a base class. Any WSDL importer
                              will
                              just use this (unique) element and doesn't need to be concerned about
                              overriding issues.

                              When gSOAP would import such as schema though, gSOAP could in fact declare
                              a
                              derived class with field 'F' to recreate the (language-specific) OO
                              hierarchy
                              with member overriding.

                              Interestingly enough, this approach allows for both OO implementations and
                              non-OO implementations to cope with schemas derived by extension. Maybe
                              I am reinventing the wheel here?

                              - Cheers, Robert


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                            • Robert van Engelen
                              ... That s an accurate observation. I came up with conventions for special characters. For example, element maps to ns2__x_DOT_y_z, assuming that
                              Message 14 of 23 , Apr 8, 2002
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                                > Thanks. I would have thought there were other potential member name
                                > issues. For example, if your programming language allows variable names
                                > to have characters that are not XML Name characters. In general, I would

                                That's an accurate observation. I came up with conventions for special
                                characters. For example, element <ns1:x.y-z> maps to ns2__x_DOT_y_z,
                                assuming that ns1 refers to the same namespace URI as ns2 (light validation).

                                This way, I can map

                                class ns__X
                                { int n;
                                };
                                class ns__Y:ns__X
                                { int n;
                                int m;
                                };

                                to

                                <?xml version="1.0" encoding="UTF-8"?>
                                <schema
                                xmlns="http://www.w3.org/2001/XMLSchema"
                                xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
                                xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
                                targetNamespace="XXXXX"
                                xmlns:ns="XXXXX">
                                <complexType name="X">
                                <sequence>
                                <element name="n" type="xsd:int" minOccurs="0" maxOccurs="1"/>
                                </sequence>
                                </complexType>
                                <complexType name="Y">
                                <complexContent>
                                <extension base="ns:X">
                                <sequence>
                                <element name="ns:Y.n" type="xsd:int" minOccurs="0" maxOccurs="1"/>
                                <element name="m" type="xsd:int" minOccurs="0" maxOccurs="1"/>
                                </sequence>
                                </extension>
                                </complexContent>
                                </complexType>
                                </schema>

                                and vice-versa. I made a change to my schema generator to accomodate
                                overriding. Is the use of the element name="ns:Y.n" valid in this case?

                                - Robert
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