• From: Nora M Dowling <ndowling@m...>
• To: Roger L Costello <costello@m...>, "xml-dev@l..."<xml-dev@l...>
• Date: Mon, 12 Oct 2020 17:26:45 +0000

Roger,

What I think is that there should be a documentation annotation in the XSD
that indicates that the first title element is for the primary title as
specified in reference document [book schema standard, dated CCYY-MM-DD]. 

In your second example, what is the assurance that only one of the title
elements will hold the primary attribute set to true? Seems like you need a
different schema. If the spec says it has to be first, and it doesn't appear
first, how the code is written will make a difference. One shouldn't infer
what the code is doing based on what is in an XML instance document. 

-Nora


-----Original Message-----
From: Roger L Costello <costello@m...> 
Sent: Monday, October 12, 2020 12:43 PM
To: xml-dev@l...
Subject:  What is the meaning of the first child element for an
element that is repeatable? 

Hi Folks,

A specification says that a book has one or more titles. Here is an example
of how the developers implemented the specification:

<Book>
    <Title>Draft No. 4</Title>
    <Title>On the Writing of Prose</Title> </Book>

The specification says that the first title is the primary title.

To obtain the primary title, the developers created an application that
queries the <Book> element for the first child <Title> element. For the
example, this <Title> element is fetched:

    <Title>Draft No. 4</Title>

Do you agree with the developer's approach to obtaining the primary title?

The developers implemented the XML Schema this way:

<element name="Book">
    <complexType>
        <sequence>
            <element name="Title" maxOccurs="unbounded" type="string" />
        </sequence>
    </complexType>
</element>

That says Book contains one or more Title elements. It says nothing about
ordering the <Title> elements. It does not say that the primary title must
always be the first child <Title> element of <Book>.

It seems to me that there is a risk with creating applications which assume
the first child <Title> element of <Book> is the primary author. Do you
agree that there is a risk? 

Do you avoid the risk?

To avoid the risk, do you add additional information to explicitly indicate
which <Title> element holds the primary title? E.g.,

<Book>
    <Title primary="true">Draft No. 4</Title>
    <Title>On the Writing of Prose</Title> </Book>

Or is that being excessively cautious?

/Roger






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• References:
  • What is the meaning of the first child element for an element that isrepeatable?
    • From: Roger L Costello <costello@m...>