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- few archetypes use anything but ITEM_TREE because it appears that one 'can never know' if some more detail will be needed later
- TB: but what about things like Apgar, Barthel etc - surely they are linear lists?
- also, it appears that some form of 'table' structure is still needed
- ITEM_TREE, ITEM_LIST etc cannot be nested inside each other arbitrarily.
- the structures complicate the software unnecessarily, without adding much value (this would clearly be true if no/limited use is being made of ITEM_LIST, ITEM_SINGLE) - [question: by "use is being made", do you mean use of the class methods in software or use of the structuring possibilities? The structuring possibilities will remain if a structure_type variable is used.]
- Depending on how you write and divide/distribute software functionality, having ITEM_STRUCTURE subclasses may just complicate class structure and not add any value at all in server/backend/query code and storage. Storing the same structure/presentation info in a structure_type variable will still give GUI code what it needs for validation and presentation but a handful of classes less to implement and maintain e.g. on the server side. Some implementations (or parts of implementations) handle openEHR structures mainly as documents, not objects, thus only stored attributes, not object methods, are used - in those cases the methods of ITEM_STRUCTURE subclasses bring absolutely no value and a structure_type variable would be easier to handle than having to store or infer object type info.
- When learning and presenting openEHR, there will be fewer classes and one level of nesting less to consider, making the design less cluttered.
- "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." - Antoine de Saint-Exupery
- archetype paths are made longer and more complex ... MORE INFO REQUIRED - WHAT'S THE PROBLEM?** Paths are used e.g. in AQL queries - shortening or simplification of paths make queries easier to read, write and understand.
- Having fewer nesting levels to traverse in hierarchical database backends (e.g. network-DBs and XML-DBs) or ORM mapping frameworks when fetching data from queries would likely improve performance.
- Shorter paths also means less to parse and translate for the query processing software, but without measuring the impact of this it is not possible to say if it matters very much for performance in practice.
- a clear solution to the pizza problem (multi-value items & UI) is needed
- add a type that is a mixture of CLUSTER and ELEMENT, i.e. has a value and also children, to allow for the fractal nature of data, with a 'summary' value, plus underlying detail
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On existing RM 1.0.2 data |
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Discussion
Questions/thoughts from Erik Sundvall:
- The above VALUE_CLUSTER sugestion is an interesting change, and if flexibility is what is sought for, then perhaps the simplification can be taken even further...
- Now the current ITEM+ELEMENT+CLUSTER follows the composite design pattern (see c2 wiki and wikipedia http://en.wikipedia.org/wiki/Composite_pattern). But since there are not many common operations/methods shared by ELEMENTs and CLUSTERs (except the ones already in PATHABLE/LOCATABLE) then perhaps the composite design pattern is not needed/helpful in this part of the openEHR structure. (Also see discussions at CompositeConsideredHarmful and maybe this.)
- If the contents of both ELEMENT and CLUSTER are pushed up to ITEM then we get the same functionality as proposed in VALUE_CLUSTER, but with fewer classes. (ITEM_STRUCTURE will not be needed, see the "Middle and Lower IM"-suggestion further down on this page, but perhaps ITEM_STRUCTURE would be a better name than ITEM for this new super-ITEM with VALUE_CLUSTER capabilities). And one (debatable) way of looking at the ITEM/ITEM_STRUCTURE family of classes is to consider them as being just for structuring and naming nodes internally in a hierarchy and considering the the DATA_VALUE classes to be the real leafs. (Yes, debatable...)
- Perhaps what is mentioned as a "downside" above (not being able to force ELEMENT or CLUSTER) is achievable (if wanted) by archetyping a new super-ITEM to have 0 items (forcing ELEMENT-functionallity) or 1..* items (forcing CLUSTER-functionality)? Also, perhaps "value" can be archetyped as disallowed if you rally want to force value-less CLUSTER behaviour.
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