[DDI-users] Documenting rates in the aggregate data extension

[Humphrey Southall]

At 16:42 09/03/2004 +0100, you wrote:
>Hi
>
>I am not sure if I understand you correctly, but why cant you use a 
>none-additive nCube for this purpose? There will of course always be 
>limits to what you can do (software-wise) with none-additive aggregates, 
>but that will always be the case independent of the metadata specifications.
>
>If you could include the raw numbers that are used to calculate the rates 
>in the cube you would of course be better off, but than you would need a 
>way to specify the actual calculation formula. This is missing in the 
>current DDI-spec. At least if this is going to provide generic solution a 
>simple aggMeth=percent" would not help you much.
>
>Jostein Ryssevik/Nesstar
The background is partly that this is an on-line visualisation system, and 
the system knows quite a lot about what it can do with nCubes provided they 
are additive.  Obviously, there are going to be numbers which have so 
little to do with anything else in the system that we cannot do much with 
them at all.  However, we can do quite a lot with a pre-computed rate, and 
most obviously we can map it (the system also holds the boundaries of those 
15,000 parishes).

Another feature of the system is that it includes an additional kind of 
entity called a rate, which has three special attributes as well as the 
usual labels and text:  a denominator, a numerator and a multiplier (e.g. 
100 for a percentage) -- i.e. a basic calculation formula.  These are used 
to create meaningful maps and time series graphs from the frequency counts 
which make up most of our data.  See 
http://tiger.iso.port.ac.uk:7778/pls/nfp/gbhweb.dds.home

Best wishes,

Humphrey Southall
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    ====================================
Humphrey Southall
Reader in Geography/Director,
Great Britain Historical GIS Project
Department of Geography, University of Portsmouth
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