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@mitre.org>
Sent: Monday, October 12, 2020 12:43 PM
To: xml-dev@lists.xml.org
Subject: [xml-dev] 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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