Re: [relax-ng] trang instance input module

[James Clark <jjc@jclark.com>]

> The comma separated list of name=value is extensible but verbose. If we
> limit the information carried in attribute values to be only the number
> of occurrences and the type, we can simplify it to:
>
> <foo bar="?, xsd:integer"/>
>
> or, if we want to draw the attention to the fact that this value has a
> special meaning, we can add some kind of brackets such as:
>
> <foo bar="{?, xsd:integer}"/>

The things about this I don't like are:

- the ? inside the attribute value: the ? conceptually applies to the 
entire attribute not merely the value

- very non-uniform with elements (although some non-uniformity seems 
unavoidable)

- attribute value with complex structure; generally I prefer attributes 
that don't require too much microparsing

Perhaps the best would be to say that literal attributes are always 
optional.  For required attributes, you have to use an element (i.e. 
eg:attribute), but the default for such an element would be that the 
attribute is required (as in RELAX NG). My thinking is that

- most of the time attributes are optional

- element syntax for attributes is least painful when the attribute is 
required

In this case, the value of a literal attribute would just specify the 
allowed value, not whether it was required/optional.  Here, one could 
follow the compact syntax and say that a name with a prefix refers to a 
builtin datatype and a name without a prefix refers to a definition.

For example,

  <foo bar="xsd:int"/>

turns into

  element foo { attribute bar { xsd:int }? }

and

  <foo bar="number"/>

turns into

  element foo { attribute bar { number }? }

For elements, we could have an eg:type attribute that allows a name with 
the same interpretation as the value of a literal attribute.  For example,

  <foo eg:type="xsd:int"/>

turns into

  element foo { xsd:int }

and

  <foo eg:type="number"/>

turns into

  element foo { number }

James