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Re: [xml-dev] XSD design question

Hi Hans-Jürgen,

I see. You'd like to share the base type among different response
types. How about defining the response type with a choice, and then
using substitution groups to specify your different response types?

Thinking out loud.

Kind regards,

On Fri, May 29, 2015 at 3:33 PM, Hans-Juergen Rennau <hrennau@yahoo.de> wrote:
> Hi Ghislain,
> this is an interesting idea, and I have not thought of that. But it seems to
> me we would then have for each operation two different response types, a
> success type and a failure type? This appears to me an increase in
> complexity perhaps not justified by the effect.
> Cheers,
> Hans-Jürgen
> Ghislain Fourny <g@28.io> schrieb am 15:28 Freitag, 29.Mai 2015:
> Hi Hans-Jürgen,
> Have you considered using a restriction rather than an extension, to
> define derived types? You could then play with occurrence indicators
> in each subtype, forbidding or allowing the one or the other.
> Kind regards,
> Ghislain
> On Fri, May 29, 2015 at 2:39 PM, Hans-Juergen Rennau <hrennau@yahoo.de>
> wrote:
>> Dear collegues,
>> I would appreciate to hear your opinion concerning an XSD design problem.
>> The goal is a general pattern for modelling web service responses which
>> are
>> required to either deliver a normal payload or, instead, deliver error
>> diagnostics. The problem at hand is whether or not to use a choice between
>> an "Errors" element and a normal payload,
>> Until now I followed a pattern consisting of such a choice:
>>        <xs:choice>
>>          <xs:element name="Errors" type="ErrorsType"/>
>>          <xs:sequence>
>>            <xs:element name="SomeData" type="xs:string"/>
>>            <xs:element name="MoreData" type="xs:string"/>
>>          </xs:sequence>
>>        </xs:choice>
>> The advantage is the clear semantics: EITHER error OR payload. Never none
>> or
>> both.
>> Unfortunately, the choice (including the error branch) canot be shifted
>> into
>> a common base type, as any extension of such a base type would come after
>> the choice, rather than extend the payload branch. Java developers
>> complain,
>> as the error structure is thus (from their point of view) repeated unduly.
>> So I wonder about the following alternative, which replaces the choice by
>> a
>> sequence: a nillable (or, alternatively, optional) error element is
>> followed
>> by the optional payload, which is provided by the response type extending
>> the base type
>>  <xs:complexType name="BaseRSType" abstract="true">
>>    <xs:sequence>
>>      <xs:element name="RS_Metadata" type="RS_MetadataType"/>
>>      <xs:element name="Errors" xsi:nil="true" type="ErrorsType"/>
>>    </xs:sequence>
>>  </xs:complexType>
>>  <xs:complexType name="FooRSType">
>>    <xs:complexContent>
>>      <xs:extension base="BaseRSType">
>>        <xs:sequence minOccurs="0">
>>          <xs:element name="SomeData" type="xs:string"/>
>>          <xs:element name="MoreData" type="xs:string"/>
>>        </xs:sequence>
>>      </xs:extension>
>>    </xs:complexContent>
>>  </xs:complexType>
>> [Note the minOccurs=0 on the sequence representing a normal payload.]
>> Advantage: the error structure has been shifted into a common base type of
>> all responses. Disadvantage: the either-error-or-payload semantics is not
>> any more captured by the schema, which would allow also an error plus a
>> payload.
>> Should you have an opinion whether to prefer the choice model or the
>> sequence model, I would like to know.
>> Kind regards,
>> Hans-Juergen Rennau
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