On 11/11/2011 5:11 AM, Thomas Beale wrote:
>
> In the current ADL 1.4-based XSDs used in openEHR, occurrences,
> cardinality and existence are expressed as XML elements. We will want
> to improve this for ADL 1.5 based XML. Now, we don't want to only take
> care of XML; we also need to make it work for JSON, and (internally)
> for dADL - neither of the latter have XML's 'attributes'. Many people
> have asked for more efficient ways of serialising. Here are some ideas
> for ADL 1.5 XML, JSON etc.
>
> ~~~~~~~~~~ first question: occurrences and cardinality ~~~~~~~~~~~~~~~~
> Occurrences and cardinality are proper intervals in the AOM
> representation. The most simplified object structure (JSON and dADL)
> for occurrences and cardinality could look as follows (I use dADL &
> occurrences here):
>
> occurrences = <
> lower = <2> -- Integer field
> upper = <10> -- Integer field
> >
>
> but the upper limit is commonly unbounded, i.e. '*' in typical
> UML-like syntax. We could do:
>
> occurrences = <
> lower = <2> -- Integer field
> upper_bounded = <True> -- Boolean field
> >
Why cant' the absence of a value mean unbounded?
occurrences = <
lower = <2>
>
Means 2..*
I vaguely remember us discussing this many moons ago but I've forgotten
the rationale..
Also, what about inclusive/exclusive values at either end
of the interval? I know that this isn't an issue for occurence and
cardinality intervals which are always inclusive - but are we proposing that
the representation of normal intervals will not use the same mechanisms
are you are proposing here?
> ~~~~~~~~~~~~~ second question:existence ~~~~~~~~~~~~
> Existence as an interval can be 0..0 (prohibited, commonly used in
> templates), 0..1 (optional, typical in the RM) and 1..1 (used in
> templates and sometimes in archetypes). Now, since archetypes and
> templates are /constraint/ structures, they can only /further
> /constrain the RM in ADL/AOM 1.5. The only possibilities for this are
> actually "0..0" and "1..1", so we could collapse existence onto a
> single Boolean for serialised representation (it could also be a
> single Boolean in the AOM, but that would be a breaking change, and
> since we already use Intervals for occurrences and cardinality, it
> does not seem worth the trouble).
>
> Thus in JSON/dADL it could be:
>
> some_attr = <
> existence = <True|False>
> >
>
> In XML:
>
> <attributes rm_attribute_name="name"*existence*="true">
> ....
> </attributes>
>
If it was just to optimize the XML I'd give this a vote of 'meh'.. but
given that existence is not really an interval because
as you say it has very few possible valid values, I think the removal of
the ambiguity by turning it into a single boolean
is probably worthwhile.
Andrew
