UIDs are only created when you create a new person, of import one that doesn’t have one, which means that most of the UIDs in my database were created when I migrated the tree made by my parents from Brother’s Keeper to PAF, somewhere around 2004.
When I moved to Gramps, in 2010, I made made sure that it imported all UIDs made by PAF, even though Gramps didn’t actually use them. And that means that most of the UIDs that I now have in my tree are about 20 years old, and stable.
When I import new branches from FamilySearch, with Ancestral Quest or RootsMagic, Gramps imports the UIDs assigned by those programs, and the same goes for persons added on-line on Ancestry, mostly from hints. They get a UID created by Ancestry, which also follows the same industry standard, adopted from PAF. This means that in my tree on Ancestry, most UIDs are the ones created by PAF, in 2004.
This means, that, if you don’t merge persons, each one has only one UID, and that’s the one that’s transferred through GEDCOM from one program to another. This also means that you don’t have a UID per application, but that you do have one per person, and tree author.
When you merge persons, most programs delete one UID, because their data model doesn’t accept more than one. And the fact that Gramps doesn’t do that is just a consequence of the way that Gramps deals with attributes, where all UIDs are stored. And in most cases, I remove one of these afterwards, because I know that most programs can’t deal with more than one, or remove one on import without telling me, which means that in my tree, it’s still one man, one UID. And by sticking to one, I know that I can follow the new composite person everywhere, because all programs that I use import that one UID. And that includes Gramps.
In a way this means that I’m the authority assigning UIDs to the persons in my tree. And when I’m careful, and don’t create the same person in two different programs, like on Ancestry and in Gramps, each person has only one UID, and no more.
And that means that, when I export this person from Gramps
0 @I0000@ INDI
1 NAME William /Trye/
2 GIVN William
2 SURN Trye
1 SEX M
1 BIRT
2 DATE 1578
2 PLAC Hardwicke, Gloucestershire, England, United Kingdom
1 DEAT
2 DATE 13 MAR 1609
2 PLAC Gloucester, Gloucestershire, England, United Kingdom
1 _UID B9F4535B0AE65341B28116E843B8F3B0AED3
1 CHAN
2 DATE 14 JUL 2023
3 TIME 21:34:58
and later export him from Ancestry
0 @I122582933599@ INDI
1 NAME William /Trye/
2 GIVN William
2 SURN Trye
1 SEX M
1 BIRT
2 DATE 1578
2 PLAC Hardwicke, Gloucestershire, England, United Kingdom
1 DEAT
2 DATE 13 Mar 1609
2 PLAC Gloucester, Gloucestershire, England, United Kingdom
1 UID B9F4535B0AE65341B28116E843B8F3B0
1 NOTE Ontleend aan “Mormonen”
he can be automatically merged by a program like PAF. I tested that today, and it still works, when I replace the UID tag in Ancestry’s GEDCOM by _UID. And this works even without the checksum, which was apparently removed by Ancestry.
PAF can merge these persons automatically, because they have the same UID, name and vitals, when compared by date and place title. And that means that in a scenario where you upload your tree to Ancestry, add a few dozen persons from hints, and change some for whom you find new sources, and then download it again, you can focus on the 1 % that can’t be merged by UID, and that’s a huge time saver, all made possible by that one UID.