It won't surprise you to learn that I like things as they are. Here are my
reasons:
1. I dispute the metric according to which:
<optional><attribute name="foo"/></optional>
is more verbose than
<attribute name="foo" occurs="optional"/>
Why is an element node plus an attribute node less verbose than two element
nodes? Are we counting characters here? If that's the case, then perhaps
we should change to <opt>, <plus>, <star> (just kidding).
2. It would complicate the spec:
(a) It would seriously uglify the simple syntax (in Section 5 of the spec).
Instead of
| <oneOrMore> nonEmptyPattern </oneOrMore>
| <group> nonEmptyPattern nonEmptyPattern </group>
we would have
| <group occurs="oneOrMore"> nonEmptyPattern </group>
| <group> nonEmptyPattern nonEmptyPattern </group>
(b) The full syntax would become more complicated. In the grammar in
section 3, in the pattern production, we would have to add an attribute to
18 or so of the choices.
(c) The transformation rules would become more complicated.
3. RELAX NG provides a number of operators that operate on one or more
patterns to produce a new pattern. At the moment all such operators are
consistenly expressed as an element. I believe this consistency contributes
both to ease of learning and ease of implementation. With the proposed
change, we would be giving special treatment to three operators. Why is it
right to treat oneOrMore as an attribute but list, say, as an element?
They are both unary operators on patterns. Surely they should be given a
consistent syntactic treatment.
4. In W3C XML Schema, although the concrete syntax uses attributes, at the
component level the repetition is a separate component (a particle). This
reflects the fact that conceptually a oneOrMore/zeroOrMore/optional
operator is logically separate from the pattern to which it is applied. In
RELAX NG, we don't have a separate component layer; rather we use a
simplified form of our syntax. I believe this is a very important
simplifying factor in the spec. However, to make this work well, we need
the concrete syntax to cleanly reflect the conceptual structure. I believe
using attributes for occurrence operators would be a step backwards in this
respect.
--On 05 July 2001 16:30 +0900 Murata Makoto <> wrote:
> Currently, to declare optional attributes, we write
>
> <optional>
> <attribute ..>
> </attribute>
> <optional>
>
> To declare a collection of many optional attributes, we write
>
> <define name="commonAttributes">
> <optional>
> <attribute ..>
> </attribute>
> <optional>
> <optional>
> <attribute ..>
> </attribute>
> <optional>
> ...
> <optional>
> <attribute ..>
> </attribute>
> <optional>
> </define>
>
> Isn't this verbose?
>
> Quite a few people in the XML Schema WG think that elements for */+/? are
> too verbose and have chosen "maxOccurs"" and minOccurs". RELAX Core has
> chosen "occurs".
>
> Cheers,
>
> Makoto
>
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