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
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