Hi Pieter, "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?"
It is an open question but one advantage of using the function approach, with simple values is that it can encapsulate the algorithm without too much dependency on understanding openEHR paths or path -bindings. That should allow broader engagement with non-openEHR specialists. My preference is to support use of openEHR datatypes within the expression (albeit perhaps in reduced format), as otherwise passing units etc as scalars starts to get cumbersome. e.g $apgar_heartrate, $apgar_breathing, $apgar_reflex, $apgar_muscle, $ apgar_colour) where each of these is actually an ordinal, rather than a scalar value. Not such a good example but think of a BMI calc, where the units used for height and weight are critical We can learn a lot from GDL experience in this regard. Ian Dr Ian McNicoll mobile +44 (0)775 209 7859 office +44 (0)1536 414994 skype: ianmcnicoll email: i...@freshehr.com twitter: @ianmcnicoll Co-Chair, openEHR Foundation ian.mcnic...@openehr.org Director, freshEHR Clinical Informatics Ltd. Director, HANDIHealth CIC Hon. Senior Research Associate, CHIME, UCL On Fri, 1 Feb 2019 at 14:53, Pieter Bos <pieter....@nedap.com> wrote: > 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 <openehr-technical-boun...@lists.openehr.org> > on behalf of Thomas Beale <thomas.be...@openehr.org> > *Reply-To: *For openEHR technical discussions < > openehr-technical@lists.openehr.org> > *Date: *Friday, 1 February 2019 at 14:16 > *To: *"openehr-technical@lists.openehr.org" < > openehr-technical@lists.openehr.org> > *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 > > > > _______________________________________________ > openEHR-technical mailing list > openEHR-technical@lists.openehr.org > > http://lists.openehr.org/mailman/listinfo/openehr-technical_lists.openehr.org >
_______________________________________________ openEHR-technical mailing list openEHR-technical@lists.openehr.org http://lists.openehr.org/mailman/listinfo/openehr-technical_lists.openehr.org
