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Re: [soapbuilders] Schema question

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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 1 of 23 , Apr 3, 2002
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      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 2 of 23 , Apr 3, 2002
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        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
        >
        >
        >
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        >
        >
      • 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 3 of 23 , Apr 3, 2002
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          >
          > 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 4 of 23 , Apr 4, 2002
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            --- 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 5 of 23 , Apr 4, 2002
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              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 6 of 23 , Apr 4, 2002
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                <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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              • 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 7 of 23 , Apr 4, 2002
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                  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 8 of 23 , Apr 4, 2002
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                    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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                    To unsubscribe from this group, send an email to:
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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 9 of 23 , Apr 5, 2002
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                      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 10 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 11 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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                          implementation and interoperability issues. Please stay on-topic.

                          To unsubscribe from this group, send an email to:
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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 12 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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