Merging GEDCOM files

Does anyone have any recommendations for applications or tools for merging GEDCOM files ?

I'm *still* trying to work out a usable solution to splitting the load between various cousins and relations. This invariably involves the probability that people will be working off two different sets of core files.

For example, say in my dataset Ned Murphy (born on 01/04/1900) who married Mary Smith is individual I00001 and is part fo family F00001 and in my cousins dataset Ned Murphy (born on 01/04/1900) who also married Mary Smith is individual I00045 and ispart of family F00013. These are clearly the same Ned Murphy and the same family, but my experience with merging files so far is that I will end up with 2 Ned Murphys and two families.

I would have thought that most intelligent programs would do some sort of logic check and synch up the two datasets based on a common key (an individual in both).

I had a quick look around for external applications which would do this and came across this one - http://www.genmerge.com/products.php?id=1.

However, is this not functionality that would be built into most genealogy applications anyway ? Is it not normal to have a large core database and need to merge another subsidiary one with it and have the application sort out the overlap instead of requiring manual review of (say) 500 people ?

Am I just missing something basic ?

z