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Re: optional, but at least one required

From: Marie Bilde Rasmussen <mariebilderas@gmail.com>
Date: Thu, 11 Oct 2007 11:19:48 +0200
Message-ID: <c36097090710110219j7a3c4eare8a6e85871b6d519@mail.gmail.com>
To: "Pete Cordell" <petexmldev@tech-know-ware.com>
Cc: "Virginia Wiswell" <vwiswell@verizon.net>, xmlschema-dev@w3.org
This syntactic workaround used to avoid UPA violation: (ab*|b) used to
express (a|ab|b) is the only way I know of  to solve the problem.



But I do think that schemas become harder to construct and very much harder
to read and communicate about when reformulated like this.


And, just as Virginia, I could use a constraint on a sequence- or
choice-element, saying that "it should contain something" (i.e. at least one
child element) to be valid, even though all the members were optional,
something like




My impression is that the negavtive impact on construction and readability
grows very fast when the number of alternatives raises.



Consider the case where we must apply the same requirements to a larger
number of elements. In my dictionary-data, I require, that entries for
homonyms are sorted after their part of speech, e.g. common nouns before
proper nouns before verbs before prepositions. There kan be 0, 1 or more
entries of every type, but my homonyms-element must contain at least one
entry. I would love to write:



<xsd:element name="homonyms">

<xsd:sequence>

      <xsd:element ref="commonNoun-entry minOccurs="0"
maxOccurs="unbounded"/>

      <xsd:element ref="properNoun-entry minOccurs="0"
maxOccurs="unbounded"/>

      <xsd:element ref="verb-entry minOccurs="0" maxOccurs="unbounded"/>

      <xsd:element ref="preposition-entry minOccurs="0"
maxOccurs="unbounded"/>

</xsd:sequence>

</xsd:element>



and be able to express some "at least one entry"-constraint at the
<xsd:sequence>-level



But I cannot do this, so I have to implement my rule this way:



<xsd:element name="homonyms">

<xsd:choice>

<xsd:sequence>

      <xsd:element ref="commonNoun-entry maxOccurs="unbounded"/>

      <xsd:element ref="properNoun-entry minOccurs="0"
maxOccurs="unbounded"/>

      <xsd:element ref="verb-entry minOccurs="0" maxOccurs="unbounded"/>

      <xsd:element ref="preposition-entry minOccurs="0"
maxOccurs="unbounded"/>

</xsd:sequence>

<xsd:sequence>

      <xsd:element ref="properNoun-entry maxOccurs="unbounded"/>

      <xsd:element ref="verb-entry minOccurs="0" maxOccurs="unbounded"/>

      <xsd:element ref="preposition-entry minOccurs="0"
maxOccurs="unbounded"/>

</xsd:sequence>

<xsd:sequence>

      <xsd:element ref="verb-entry maxOccurs="unbounded"/>

      <xsd:element ref="preposition-entry minOccurs="0"
maxOccurs="unbounded"/>

</xsd:sequence>

<xsd:sequence>

      <xsd:element ref="preposition-entry maxOccurs="unbounded"/>

</xsd:sequence>

</xsd:choice>

</xsd:element>



In real life, we have about 15 different kinds of entries, so you can
imagine how overwhelming that part of the schema is.


I guess some of you will now tell me to use Relax NG instead. Unfortunatley,
I don't have that option. So I am not asking for an answer or solution,  I
would just like to hear some opinions on the issues.


-Marie



**********

Marie Bilde Rasmussen

editor, MA BSc

Gyldendal Publishers, Copenhagen (Denmark)

(dictionaries)

www.gyldendal.dk

**********


2007/10/11, Pete Cordell <petexmldev@tech-know-ware.com>:
>
>
> To be pedantic, removing the second <xsd:element ref="a"/> prevents the
> Unique Particle Attribution violation for _a_.  We then need to work
> around
> this change by adding minOccurs="0" to element b so we allow what we want.
>
> :-),
>
> Pete.
> ----- Original Message -----
> From: "Virginia Wiswell" <vwiswell@verizon.net>
> To: "Pete Cordell" <petexmldev@tech-know-ware.com>; "Virginia Wiswell"
> <vwiswell@verizon.net>
> Cc: <xmlschema-dev@w3.org>
> Sent: Thursday, October 11, 2007 2:35 AM
> Subject: Re: optional, but at least one required
>
>
> >
> > So the minOccurs="0" on element b prevents the Unique Particle
> Attribution
> > violation for b?
> >
> > This is perfect, Pete. Thanks so much for helping me out.
> >
> > On Wed, 10 Oct 2007 19:22:51 +0100
> >  "Pete Cordell" <petexmldev@tech-know-ware.com> wrote:
> >>
> >> Hi Virginia,
> >>
> >> Your schema should indeed yield a Unique Particle Attribution
> violation.
> >> The reason is that when a parser reads element a, it is not immediately
> >> obvious whether it corresponds to the first definition of a or the
> >> second.
> >>
> >> You can get around this by changing your schema to:
> >>
> >>  <xsd:element name="parent">
> >>   <xsd:complexType>
> >>    <xsd:choice>
> >>      <xsd:sequence>
> >>        <xsd:element ref="a"/>
> >>        <xsd:element ref="b" minOccurs="0"/>
> >>      </xsd:sequence>
> >>      <xsd:element ref="b"/>
> >>    </xsd:choice>
> >>   </xsd:complexType>
> >>  </xsd:element>
> >>
> --
> =============================================
> Pete Cordell
> Codalogic
> for XML Schema to C++ data binding visit
> http://www.codalogic.com/lmx/
> =============================================
>
>
>
>
Received on Thursday, 11 October 2007 09:19:57 GMT

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