dhis2-devs team mailing list archive

[Bob Jolliffe <bobjolliffe@xxxxxxxxx>]

OK.  I've reached the conclusion that the model can and probably should be
simplified, but it is really far too much work for what I have time for
now.  The categoryoptioncombo is already deeply ingrained in many parts of
the system.  So don't hold your breath.

I'm going back to focus on my much simpler problem of exploding
categorycombooptions into dimensions and vice versa.

For querying, I can see the API needs methods added to return datavalues by
arbitrary collections of category rather than just fixed
categoryoptioncombos.  These only exist for the purpose of data collection.
I suspect that this is what Ola needs to create more flexible reporttables.
Then when configuring the reporttable you would freely select the dimensions
you were interested in.  This is of course do-able - I can see it - but my
little brain is struggling with the complexity.

Looking at a two stage process it is a matter of getting the collection of
categorycombooptionids which intersect with the given set of categories and
then passing that collection to the existing API method which returns
collections of  datavalues which match particular categorycombooptionids.

In principle if we can expose the required methods in the API then it might
be possible at some time in the future to revamp the underlying table
structure without disturbing the API.

Two final thoughts:
1.  if we are bound to the model whereby categoryoptions are free standing
entitities (ie many to many relation with categories) then, for the purpose
of import/export we are obliged to uniquely identify these as well.  So I
will have to reluctantly also put uuids on categoryoptions.  After
discussing with Abyot last night, I can see that there is some value in
having them the way they are, but we will have to live with the complexity.
What you gain on the swings you lose on the roundabouts.

2.  Indicators are not multidimensional.  Why is this?  Was it a conscious
decision resulting from earlier discussion or is it just that we haven't got
there yet?

Regards
Bob

2009/9/29 Bob Jolliffe <bobjolliffe@xxxxxxxxx>

> 2009/9/29 Abyot Gizaw <abyota@xxxxxxxxx>
>
>>
>>
>> On Tue, Sep 29, 2009 at 9:16 PM, Jason Pickering <
>> jason.p.pickering@xxxxxxxxx> wrote:
>>
>>> I think Abyot raises some good points, especially his last one about
>>> differenences of what the age dimension really is.
>>>
>>> I think the biggest challenge is going to be how to unite the concepts
>>> of a multidimensional data element (as it is currently implemented
>>> with categories) and a data element that has no multidimensionality,
>>> at least in the sense of it not being assigned any categories.
>>>
>>
>> Isn't this what we have in the current system? If you are not assigning
>> any combination of categories for a dataelement (well of course for the sake
>> of consistency - from programming logic point of view - implicitly a default
>> category combination with one default category having one default option is
>> assigned - it is like putting your value at zero on the dimensions axis)
>> then the dataelement has no dimensionality.
>>
>
> I don't really like the default category idea.  The way I have currently
> proposed there is no default category.  By default a dataelement has no
> dimensions.  It doesn't need a default dimension.  And also by default the
> dimensionelementcombination in datavalue is NULL.
>
>
>>
>>
>>>
>>> What about the following scenario. Could the cateogry/category combos
>>> be transformed somehow into a sort of data element generator? Users
>>> could define a dimensionality set, assign a master data element, and
>>> DHIS would create all of the necessary data elements. So a category
>>> combination of Patient Status (OPD, IPD, Deaths) and Age (Under 1
>>> ,Under 5 and Over 5) and template data element (Clinical malaria)
>>> would produce :
>>>
>>> OPD Under 1 Clinical Malaria {OPD, Under 1, Clinical Malaria}
>>> OPD Under 5 Clinical Malaria {OPD, 1-5, Clinical Malaria}
>>> OPD Over 5 Clinical Malaria ...
>>> OPD Clinical Malaria Total {OPD, All ages, Clinical Malaria}
>>> ...
>>> ..
>>> ..
>>> IP Clinical Malaria Total {IP, All ages, Clinical Malaria}
>>> ...
>>> ...
>>> ...
>>> Deaths Clinical Malaria Total {Deaths, All ages, Clinical malaria}
>>> Clinical Malaria Total {All patient status, All ages, Clinical malaria}
>>>
>>> Each one of those data elements would then be assigned a set of
>>> dimensions, and a set of dimensional elements.
>>> The cateogries functionality would simply be an artifact to produce
>>> multiple data elements, without having to enter them seperately, which
>>> if I understood Ola yesterday, was one of its intended purposes.
>>>
>>> Now, for those of use such as myself, that do that have already create
>>> dozens of data elements with different dimensions in their names (but
>>> no where in a relational table) we could assign the dimensionality in
>>> a seperate step (post-facto as Bob mentioned earlier). I might want to
>>> assign a "uber" dimension of "Communicalble" and "Non-communicable" to
>>> a disease type that might not have anything to do with the definition
>>> of the data element itself, but would be simply for analysis purposes
>>> later.  Again, I may be rehashing my previous emails here, but from a
>>> pure SQl standpoint, the approach I suggest here makes sense to me, in
>>> terms of queries of how to pull this into a crosstab as well as how to
>>> generate a fact table that something like an OLAP server could deal
>>> with
>>>
>>> This approach might seem to resolve the issue of how to deal with
>>> these two different beasts, but unfolding the multidimensional data
>>> element into simpler components. Meaning that the
>>> cateorgy/combos/options would be used as a templating mechanisms, but
>>> that dimensionality could be assigned through a separate set of
>>> relations.  Perhaps this is what is represented in the diagram, but I
>>> will need to study it tomorrow after some sleep.
>>>
>>> I do think that that dimenional elements should not be able to be
>>> share by dimensions, and that dimensions and dimensional elements
>>> should not be able to be deleted without lots of bells and whistles
>>> going off once they have been assigned to data elements.
>>>
>>
>> What is wrong with that as long as values are not associated with them? I
>> think we will be falling back to the current implemention instead - like
>> dimensional elements should not be deleted once values are assigned to their
>> combinations.
>>
>
> I agree.  I think we all will agree on this much.
>
>
>>
>>
>>>
>>> I guess the key question is whether data elements should be able to
>>> have multiple DimensionElementCombinations, which I think is the
>>> current implementation. I am just not sure this will work with a
>>> combination of DHIS2-type-multidimensional elements, and DHIS1.4-type
>>
>> data elements.
>>>
>>
>> Can anyone explain me how the DHIS2 multidimensional dataelement concept
>> fails to handle the DHIS 1.4 dataelements - sorry may be I missed this from
>> your earlier discussion? I think the way I see it - if the objective is on
>> OLAP, pivoting/querying, then what we need is not to change the model -
>> instead to develop more APIs which can pull data along a dimension, varying
>> degree of overlappings across dimensions - or more generally aggregation of
>> values over a flexible set of dimensionelementcombinations !
>>
>
> Again I am with you mostly on this.  In fact that has been my suggestion
> all along - to push the functionality into the API.  But having said that I
> think the current model is too double-jointed and complex.  I have seen by
> trying to unpick the dimensions using xslt I need too many hash tables which
> is inefficient.  This no doubt would also translate into too many SQL
> clauses.  By trimming the requirement that dimensionelements are freely
> assignable the model becomes a good bit simpler.  Beyond that it is mostly
> changing names.
>
>
>>
>> Using the example above -  {OPD, IPD}, {Male, Female},{Under 1, 1-5, Above
>> 5} and malaria as base dataelement
>>
>> What we have currently is an API to provide values for
>>
>> Malaria(OPD,Male,Under 1)
>> Malaria(OPD,Male,1-5)
>> Malaria(OPD,Male,Above 5)
>> Malaria(OPD,Female,Under 1)
>> Malaria(OPD,Female,1-5)
>> Malaria(OPD,Female,Above 5)
>> ....
>> ...
>>
>> And if I understood correctly .. what is required is to have registred
>> cases of
>>
>> Malaria in the OPD,
>> Malaria in the IPD
>> Malaria for Males
>> Malaria for Females
>> ....
>> ..
>>
>> Malaria In the OPD but only those Female
>> Malaria In the IPD but for male
>> ..
>> ..
>> ..
>> we can list different combinations....
>>
>> or finally ask ...... for the Malaria
>>
>> Isn't this a simple question of Aggregation? Does the multidimensional
>> datamodel have a limitation to handle the above requirements - or am I
>> talking a different stuff here?
>>
>
> No I believe it can probably be done - but yet it doesn't seem to have been
> done.  When I started looking at how I might do it I realized that it could
> also be simplified.
>
> Regards
> Bob
>
>
>>
>>
>>>
>>> Enough for today.
>>>
>>> Thanks for this Bob. It is a good start.  Can't you make this diagram
>>> in DocBook so I can edit it? :D
>>>
>>> Regards,
>>> Jason
>>>
>>>
>>>
>>> On Tue, Sep 29, 2009 at 8:01 PM, Abyot Gizaw <abyodia@xxxxxxxxx> wrote:
>>> > Yes your suggestion is doable and less is better .... but I think the
>>> > requirement from the field is more complex.
>>> >
>>> > If, for a moment, we stop talking about datavalues and talk about
>>> > dataelements - why are we talking about dimension combinations?
>>> >
>>> > Because you are assuming a dataelement to have only one dimension. Am I
>>> > correct? If that is the case, I see a little bit of inconsistency here.
>>> > DataElement talks about one dimesion, but its corresponding value talks
>>> > about combination of dimensions.
>>> >
>>> > Yes from the datavalue I can have dimensionelementcombinations, pick
>>> > dimensionelments regroup and put them in their corresponding dimesions
>>> -- in
>>> > the end telling me from which dimension they came from. But from this
>>> point
>>> > onwards I am no more talking about a value of a single dataelement but
>>> a
>>> > value for combination of dataelements (because I have to pull different
>>> > dataelements which can give me the identified dimensions) .... but is
>>> this
>>> > what we want?
>>> >
>>> > The other point I would like the raise is - will there not be any
>>> limitation
>>> > on the flexibility of the system when putting the restriction "A
>>> Dimension
>>> > has many DimensionElements.  But a DimensionElement is a member of only
>>> one
>>> > Dimension" ? Not only system flexibility problem, I see a logical
>>> problem as
>>> > well. Because if we think for example beyond the obvious
>>> > SEX(male,female,unknown) - I see a strong need for letting
>>> dimensionelements
>>> > to be member of multiple dimensions: For example take the other obvious
>>> > dimension - AGE. And assume <5 yrs, 5-10 yrs, and <5 yrs as its
>>> > dimesionelements. May be such scaling of the AGE dimension is
>>> approrpiate
>>> > for Malaria case, but for TB case people might be interested to break
>>> the
>>> > AGE dimension into <5yrs, 5-10yrs, 10-15yrs, >15yrs - so how are we
>>> going to
>>> > handle cases like this? Are we going to define a number of <5yrs or are
>>> we
>>> > going to use the same <5yr dimensionelement ?
>>> >
>>> >
>>> > Thank you
>>> > Abyot.
>>> >
>>> >
>>> >
>>> > On Tue, Sep 29, 2009 at 4:45 PM, Bob Jolliffe <bobjolliffe@xxxxxxxxx>
>>> wrote:
>>> >>
>>> >> OK.  Here's my first attempt to rationalize things.  Please excuse the
>>> >> attachments.  I try not to send attachments to mailing lists but these
>>> are
>>> >> at least fairly small.  (And Lars I will write it up in docbook after
>>> >> fishing for feedback).
>>> >>
>>> >> My primary aim has been to disturb the existing model as little as
>>> >> possible whilst trying to simplify wherever possible.
>>> >>
>>> >> Attached oldmodel.png shows the participants in the existing model.
>>> As
>>> >> you can see there are 11 tables in all.  I haven't showed the
>>> relations as
>>> >> it becomes a bit of a web.
>>> >>
>>> >> Also attached is a proposed amended database model which bears
>>> sufficient
>>> >> similarity to the old that migration between the two should be
>>> feasible.
>>> >> But it is down to 6 tables.  And I have named the tables according to
>>> the
>>> >> terms we have been discussing.  Of course this is just the database
>>> model.
>>> >> I've also put together an XML view of what some sample dataset might
>>> look
>>> >> like.  There is also a UML model required which would be richer than
>>> the
>>> >> underlying datamodel, but one step at a time ....
>>> >>
>>> >> Walking through:
>>> >>
>>> >> 1.  DataElements can have Dimensions.  And different dataElements can
>>> (and
>>> >> hopefully will) share some of the same Dimensions.  So there is a
>>> m-to-n
>>> >> relationship between the two necessitating an extra table
>>> >> (DataElementDimensions).  An example of a Dimension is SEX.  Nothing
>>> new
>>> >> here.
>>> >>
>>> >> 2.  Dimensions have DimensionElements.  So SEX for example might have
>>> >> DimensionElements "Male", "Female", "Unknown".  A big difference from
>>> the
>>> >> old model is that there is 1-n relationship between DimensionElements
>>> and
>>> >> Dimensions.  A Dimension has many DimensionElements.  But a
>>> DimensionElement
>>> >> is a a member of only one Dimension.
>>> >>
>>> >> 3.  DataValues represent the values at intersection of these
>>> Dimensions.
>>> >> Keeping with the spirit of the old model this intersection is
>>> represented by
>>> >> a single key, DimensionElementCombination.  The
>>> DimensionElementCombinations
>>> >> would be populated when a new Dimension is added to a DataElement.
>>> Like the
>>> >> original model there is some fragility here.  Changing dimensions on
>>> >> dataelements could create a situation where datavalues become orphaned
>>> or
>>> >> misdirected.  The API must have robust methods for defending this
>>> integrity
>>> >> particulalrly when updating the structural metadata.  But this is
>>> perhaps
>>> >> doable.  Either way its not worse than we have.
>>> >>
>>> >> I haven't given a name to DimensionElementCombinations.  From the
>>> examples
>>> >> I have seen from SL this seems to be unnecessary.  The names I have
>>> seen
>>> >> being used are generally simply contrived from the dimensions or
>>> (worse
>>> >> still) from the categoryoptions.  What is important is that
>>> dataelements can
>>> >> have sets of dimensions.
>>> >>
>>> >> And then much of what is different is just a renaming of the original
>>> >> entities.    From the attached XML file I think you can see some of
>>> the
>>> >> issues faced re names and identifiers.  I find myself following a sort
>>> of
>>> >> convention of CODE, Name, Description and UUID.  CODE's must be unique
>>> >> within the scope of the database.  I suppose this is close to what we
>>> >> currently call ShortName.  I would like to place constraints on CODES
>>> in
>>> >> terms of length and also the disallowing of spaces and other funny
>>> >> characters.  The reason being that we may well have to use these codes
>>> in
>>> >> making up uri's.  So CODES must be unique.  For the moment we could
>>> keep
>>> >> name unique but should migrate from it.  Its a matter of rewriting all
>>> our
>>> >> comparators I guess.  UUIDs I am told are unique through some sort of
>>> >> divinity so we apparently do not need to worry about them :-)
>>> >>
>>> >> I've also tried to reduce the number of knees on the donkey - from 11
>>> >> tables to 6.  I believe this can be done whilst preserving the
>>> existing
>>> >> functionality.  This arangement would make it much more sensible to
>>> produce
>>> >> the XML I need to produce.  I'm hoping that it would also be more
>>> friendly
>>> >> to those who would be trying to pivot the data across dimensions.
>>> >>
>>> >> Jason do you think this works for you?  I might have missed out
>>> something
>>> >> really fundamental.  Abyot, you've been through this process before -
>>> am I
>>> >> missing something?  From the DataValue you can see DimensionElements.
>>> And
>>> >> once you know a DimensionElement you also know the Dimension to which
>>> it
>>> >> belongs.  I think thats queryable.  Will have to hydrate with some
>>> data and
>>> >> see.
>>> >>
>>> >> Shaking the multidimensional model up like this would obviously have
>>> >> implications.  But I suspect most of it is taking stuff away rather
>>> than
>>> >> adding new so it might just be doable.  Less is more.
>>> >>
>>> >> Not spending time with docbook yet, till I get some feedback.
>>> >>
>>> >> Cheers
>>> >> Bob
>>> >>
>>> >> 2009/9/29 Bob Jolliffe <bobjolliffe@xxxxxxxxx>
>>> >>>
>>> >>> Hi
>>> >>>
>>> >>> On the back of Jason and others comments, I've reached the conclusion
>>> >>> that we cannot really live with the MD model the way it is.  Whereas
>>> I think
>>> >>> it is (just about) workable there are some serious optimizations we
>>> can and
>>> >>> should do.  I am going to put my other work back a day or two and
>>> propose
>>> >>> some changes in a branch.
>>> >>>
>>> >>> I think central to the inefficiency is the many-many relation between
>>> >>> categories and categoryoptions.  This strikes me as illogical as well
>>> as
>>> >>> being cumbersome in the UI.  Do we really want to be able to make
>>> categories
>>> >>> with options like {'0<5','6-10','Male','Out of stock','35-40'}.
>>> Reducing
>>> >>> the relation between categories and category options to 1-n cuts two
>>> tables,
>>> >>> should make sql queries more efficient and grokkable and also matches
>>> other
>>> >>> models such as sdmx better.
>>> >>>
>>> >>> The other possiible inefficiency is the dimensionset.  It can be
>>> useful
>>> >>> in some contexts but I'm guessing that when querying the data (which
>>> we want
>>> >>> to be fast) it is not relevant.  A dataelement can have dimensions.
>>> The
>>> >>> fact that some dataelements have the same combinations of dimensions
>>> is very
>>> >>> useful to know for some purposes, but it should be possible to get
>>> from the
>>> >>> dataelement to the dimension directly.
>>> >>>
>>> >>> On the other side of the road is the hierarchical dimensionality idea
>>> I
>>> >>> see Ola and Jason have been discussing, where dimensions are composed
>>> >>> (perhaps post-facto) of uni-dimensional dataelements rather than
>>> decomposed
>>> >>> into pre-structured dimensional elements.  I suspect that:
>>> >>> 1.  we need both; and
>>> >>> 2.  from the API, user and reporting perspective they should look the
>>> >>> same (ie a dataelement can have dimensions - how they come about
>>> should not
>>> >>> be a concern at the end point).
>>> >>>
>>> >>> I'll try out some of these ideas and point you to the branch.
>>> >>>
>>> >>> Regards
>>> >>> Bob
>>> >>>
>>> >>> 2009/9/29 Lars Helge Øverland <larshelge@xxxxxxxxx>
>>> >>>>
>>> >>>>>
>>> >>>>> Thanks for the explanations Jason. The multidimensional model is
>>> quite
>>> >>>>> complicated, is poorly documented, and as you say is DHIS-centric
>>> in the way
>>> >>>>> that it is built around the DHIS notion of a Data Element.
>>> >>>>>
>>> >>>>
>>> >>>> Could we assemble and put some of the text being written on the list
>>> to
>>> >>>> docbook?
>>> >>>>
>>> >>>>>
>>> >>>>> That said, and I think Jason already has made a strong case for
>>> this,
>>> >>>>> also in a 100% DHIS2 scenario you will need more flexibility in
>>> defining
>>> >>>>> dimensions to your data than what categories can provide. Being
>>> able to
>>> >>>>> define data dimensions independent of data collection is powerful
>>> and should
>>> >>>>> be supported in a better way than what data element groups provide
>>> today.
>>> >>>>> Given that we already have the orgunit group set code in place I
>>> would
>>> >>>>> assume that adding group sets to data elements could be a
>>> relatively
>>> >>>>> straight forward thing to do (but then again, I am not the
>>> programmer...).
>>> >>>>
>>> >>>> I don't see any implications in adding this to the system, it won't
>>> >>>> require changes to the existing model as the association goes from
>>> the
>>> >>>> groupset to the groups. We can prioritize this for the 2.0.3
>>> release.
>>> >>>>
>>> >>>>
>>> >>>> _______________________________________________
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>>> >>>>
>>> >>>
>>> >>
>>> >>
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>>> >
>>> >
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>>>
>>
>>
>