Re: Genealogical evidence and data model

Tim Powys-Lybbe wrote:
> In message of 20 Jan, Ian Goddard <goddai01@[EMAIL PROTECTED]
> wrote:
> 
>> singhals wrote:
>>> But, I'd venture to suggest that out of any 100 
>>> genealogists at least 51% _still_ want a program to record their 
>>> conclusions so they can print it out.  
>> If that wish were properly implemented things wouldn't be so bad.  But 
>> when I get back to the mid C18th the only conclusion for quite a number

>> of lines is "A or B" or even "A or B or C".
>>
>> S/W which assumes that pedigrees can always be resolved unambiguously 
>> won't handle this situation.  I can't believe that the situation is 
>> uncommon so how do users of such S/W cope?  Do they simply stop
entering 
>> their results when they get back to an ambiguity?  Do they allow their 
>> S/W to dictate to them that they should choose what might at the time 
>> appear to be the most likely ancestor and discard the rest?  Do they 
>> generate parallel universes of databases to handle all the alternative 
>> combinations?
> 
> I detect here, though I could be wrong, a thesis that it is possible to
> prove facts by logic.  Computers are products of logic.  So computers
> can easily prove genealogical facts.
> 

No. It's simply remarking on the fact that if the designer of a program 
assumes that the data will fit an unambiguous structure then they will 
fail to design a program which can handle alternatives.  And asking what 
users do when confronted with a situation which the designer has not 
envisaged.

> Regrettably this is not logic.  Logic is not about truth claims, it is
> about the rules of truth claim and thus its subject is all statements
> whether true or false.

Ah, I see how I misled you.  I wasn't using "or" as a logical operator 
but simply saying that, for example, "Mary Collier who was the bride in 
this marriage was either Mary daughter of George Collier whose baptism 
is recorded in record A or Mary daughter of Abel Collier whose baptism 
is recorded in record B".

> 
> If you want to establish facts you have got to give reasons and state
> that these, to you, imply certain conclusions.  Others can then see what
> you are on about and make decisions on whether they agree or not.  That
> is the fun of human discourse.
> 
> For my money, then, if you have some vague or inconclusive data, you
> should set it out and your comments in Notes to the people concerned.
> If you think that your arguments give a heavy balance of probabilities
> of identifying a person, then say that and, even, put that person in
> your database with the presumed connections.

This is where things start to get problematic.  The S/W I've seen would 
do this, in the example I gave, by merging Mary Collier the bride with 
one of the Mary Colliers who was baptised with little or no provision of 
demerging if subsequent informations shows the initial choice to have 
been wrong.

A better way of handling it would be to keep as separate the entities 
representing the bride and the baptisms and provide a field in one of 
the entities which can record the link to another.  All that's then 
needed in the event of a change of mind is to null out this field.  An 
even better way of handling it would be to provide a different type of 
entity which is a link.  The link would be a better place to hold the 
arguments and an *****sment of their strength.  It would even be 
possible to use such an entity to hold a negative association e.g. 
"these are different people".  Using a separate entity for this purpose 
makes it much easier to record the alternatives as one can provide as 
many alternative links as required.

> 
> This sort of problem gets all the more acute if you go into dealing with
> medieval people where the surviving do***ents are very few and can be
> difficult to interpret.  But this does not mean that it is impossible to
> establish a genealogy.  Though it should mean that medieval genealogy is
> a far better exercise of reasoning and discussion than any other,
> because there are so many people who share an interest in the small
> numbers of people whose records have survived.   Of course, like so many
> areas of human debate, sometimes tempers can and do get a little frayed!
> 
I know - I read s.g.m!

-- 
Ian

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