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Frequency

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Frequency

by welshofficer » Fri Mar 03, 2017 5:05 pm

How does Frequency work? I was hoping to look for taxa with 3 or fewer records in a county, so grouped by taxa and frequency >=3.

However, this gives some surprising results. I assume it's accounting for duplicates but on clicking on the results for some of the taxa with a frequency of 3, I came up with significantly more records - even more distinct monads/ tetrads.

I thought it might not be unreasonable to ignore older records or duplicates or hectads, but this seems more than that!

Polly
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Re: Frequency

by welshofficer » Fri Mar 03, 2017 5:18 pm

Ah, I think I've worked it out. It does work as I expect, but the example was Allium ampeloprasum. There are three records of the species but also 13 records of subsp. babingtonii which also come up when you search for A. ampeloprasum.
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Re: Frequency

by admin » Fri Mar 03, 2017 5:24 pm

Hi Polly,

Thanks for the example.

This does look like incorrect behaviour - it's completely illogical that grouping should ignore infra-specific taxa.

The query works better if, instead of grouping by 'taxon name (including qualifier and authority)' you instead use 'species (excluding higher ranks)':

https://database.bsbi.org/search.php#re ... 2a27e4199f
Tom Humphrey
Database Officer, Botanical Society of Britain and Ireland (BSBI)
c/o Centre for Ecology and Hydrology,Maclean Building, Crowmarsh Gifford, Wallingford, Oxon, OX10 8BB, UK.
tom.humphrey@bsbi.org
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Re: Frequency

by welshofficer » Fri Mar 03, 2017 5:33 pm

Interesting, but still not perfect. That way it comes up with species including s.l. and if you click on them you also get the taxa within the s.l.

I'm not worried about it, as long as I know how it's working!

Thanks,

Polly
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Re: Frequency

by admin » Fri Mar 03, 2017 6:08 pm

Efficient hierarchical grouping needs more work. The problem is that currently, to do it strictly correctly would result in queries that would be unacceptably slow. Instead I use some short-cuts that are optimised from grouping by species but break in some cases, for example s.l. aggregates and also with some problematic rose hybrid hierarchies (where distinct f x m and m x f parent combinations muck things up).

I need a better solution that works properly in all cases. That would allow better aggregate treatment of microspecies - e.g. allowing for the possibility of grouping Taraxacum at section level rather than at species - something that would be useful for the My County survey coverage reports.

The DDb taxon hierarchy has some 'interesting' complexities, e.g.
Ilex aquifolium 'Variegata' is a direct child of both Ilex aquifolium and Ilex cv. (and ought to appear as part of both of those in a grouped search) but Ilex aquifolium is not a child of Ilex cv.
Tom Humphrey
Database Officer, Botanical Society of Britain and Ireland (BSBI)
c/o Centre for Ecology and Hydrology,Maclean Building, Crowmarsh Gifford, Wallingford, Oxon, OX10 8BB, UK.
tom.humphrey@bsbi.org
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