dhis2-devs team mailing list archive

[Lars Helge Øverland <larshelge@xxxxxxxxx>]

Just a quick battlefield story from what we experience in Sierra Leone where
we are facing insufficient internet connectivity and must resort to offline
deployments. The districts are quite rural and we experience an "offset"
when distributing new databases (metadatasets), which means that for each
update there will be districts that still exports data to the national
server using the previous metadataset for some time until the new set has
percolated completely.

Like Bob says we deal with different types of changes, the ones I can think
of are

1) Adding of elements (dataelements, orgunits) (in the national database)
2) Removal of elements (in the national database)
3) Updates of element names/properties (in the national database)

The point of departure is that the current solution where an export message
contains both data and metadata and we match on the display name of elements
is not appropriate, and that we will move to using dedicated, agreed and
stable metadata identifiers of some sort. As Jo says we are not planning for
versioning in 2.0.7.

For the current solution the implication of the mentioned changes
when importing data from the out-of-date districts into the national
database for the change types respectively are as follows:

1) No data will come in. No problem.
2) Old metadata elements will continue to come in. Minor problem.
3) Metadata elements and its data which represents the same element will
come in but under a different name. Big problem and source for complete
chaos.

With the new proposed solution with stable metadata identifiers the
situations is like this when receiving data from the out-of-date districts:

1) No data will come in. No problem. As before.
2) Data will be ignored as the metadata identifier will not match anything
in the national database. No problem.
3) Data will match on the stable identifier even if the name/properties are
changed. No problem.

So in the offline deployment of the "regular" DHIS scenario this move will
be a huge improvement. It might not be perfect and there might be situations
I have not thought about but it will help to alleviate the bigger problems.

I am not sure how relevant this is in Jo's mobile scenario.

Lars

PS. That said I am not sure how appropriate the versioning paradigm is in
this scenario. What if you want to change the name or add an element in the
national database, should we then deny all out-of-date districts to report
any data at all? Can we live well with what is described above?