About the calculation:
Ah, I see, the assignment seems like a good solution. But why would I need a
function to calculate a score that is just a sum of a number of values, instead
of a few +-operators?
Multiplicities/data binding:
The there exists case is clear. However, what if I have four events, all having
four elements, each with dv_quantity as value. Say I want the magnitude of the
last of these quantities to be larger than the sum of the first three. Before I
could write something like:
for_all $event in /data/events[id3]
$event/data/items/element[id6]/value/magnitude >
$event/data/items/element[id4]/value/magnitude +
$event/data/items/element[id5]/value/magnitude +
$event/data/items/element[id6]/value/magnitude
(I omitted a few node ids here that are not important for the example)
Not the most readable - but it does the job. With data binding, how do I
express this? There no longer seems to be a path lookup outside of data
binding, so I can’t write:
for_all $event in $events
$event/data/items/element[id6]/value/magnitude >
$event/data/items/element[id4]/value/magnitude +
$event/data/items/element[id5]/value/magnitude +
$event/data/items/element[id6]/value/magnitude
And binding all the separate paths to variables doesn’t work either – they will
be bound as lists, and there is no way to iterate over four lists of values at
once.
Note that a path that points to a single typed dvquantity in an archetype can
still point to many items in the RM if somewhere up the tree there is a list or
a set, for example more than one observation. So if you really want them to be
typed on validation time, you need to check every attribute in the path to see
if it can point to more than one value, then either make it a
List<List<Integer>> or define in which order to add it as a single list.
I implemented it by determining type at runtime, but it’s possible otherwise.
This means that very often you need a for all statement, in which case data
binding doesn’t really help. I defined some tricks with the basic operators
also working on equally sized lists to make things a bit easier to understand
for modelers. That’s why I asked about the execution rules. The tricks I did
can be easily rewritten into for_all statements if we need to have them removed.
This leads to more interesting cases when you flatten rules to an OPT 2
template, to obtain a single artifact that can be used for many things,
including rule evaluation. That is very doable right now by prepending some
paths and adding some for_all statements. I’m not sure how to do that with data
binding.
Regards,
Pieter Bos
From: openEHR-technical <[email protected]> on behalf
of Thomas Beale <[email protected]>
Reply-To: For openEHR technical discussions
<[email protected]>
Date: Friday, 1 February 2019 at 14:16
To: "[email protected]" <[email protected]>
Subject: Re: Rules in archetypes - what are the requirements?
Thanks Pieter,
this is very useful.
On 01/02/2019 12:54, Pieter Bos wrote:
For us the main requirement of the rules is to calculate the value of other
fields based on other fields. Only the checking of assertions has relatively
little added value for the use cases our customers encounter. I would find it
very hard to explain to any users or modelers that they can write checks that
do the actual score calculation, but that they cannot actually use the
calculated value anywhere. So we ignore this limitation altogether.
the obvious solution to that requirement seems to be to a) use functions and b)
to allow assignment:
rules
-- assert that manually set total is correct
check $apgar_total_value == apgar_total ($apgar_heartrate_value,
$apgar_breathing_value, $apgar_reflex_value, $apgar_muscle_value,
$apgar_colour_value)
rules
-- assign total value
$apgar_total_value = apgar_total ($apgar_heartrate_value,
$apgar_breathing_value, $apgar_reflex_value, $apgar_muscle_value,
$apgar_colour_value)
Also the value binding seems to have an case that has not been covered:
it is possible that a single path lookup results in a list of values. This
means a single path-bound variable will contain multiple values (so a list of
values). In the old case, you could handle this with a for_all statement to
express that the assertion should be valid within the scope of a single event,
for all events. How could value binding solve this? The same question applies
to output variable binding as well as input variable binding.
conceptually, rules statements are typed, so in this case, the type will be
List<Real> or List<DvQuantity> or whatever. In that case, expressions need to
treat it in the normal way, i.e. with List or Set operators that obtain single
values. E.g.
$systolic_bp_samples: List<Real>
there_exists v in $systolic_bp_samples : v > Systolic_bp_threshold implies ....
These kinds of things (and for_all) are documented in the Expression Language
draft<https://specifications.openehr.org/releases/LANG/latest/expression_language.html#_collection_operators>.
Related to this, both the current and proposed specification is missing
execution rules, especially when paths lookup to a list of values instead of a
single variable and how to handle that. For example what does the following
mean when /data/events/data/items/element[id3]/value/magnitude resolves to more
than one value?
I don't see how it can, since that path is defined to be of type Real (not
List<Real> or Set<Real> etc) by the RM definition of DvQuantity. But I'm
probably missing something in the sense of your question...
Anyway, the more I can find out about current requirements, working solutions,
workaround etc, the better - the intention is to evolve the expression facility
in archetypes to match those needs and to be as useful as possible.
- thomas
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