To keep genealogy files manageable, enable easy sharing, and make special reports, you will want to keep the file size at less than 5,000 persons and maintain a logical branch of your relations.  The logic may be based on the contributors to your data, ancestry, location, or special needs.  What ever the reason, the task is easy if planned in advance, but in most cases, the task will be complex because the data base became too cumbersome to handle or you wish to share a meaningful portion with another relation.

The steps discussed will use terms relevant to PAF software but are applicable in process within most genealogy software.  [Please note that some genealogy software have this ability built-in, but most do only ancestor and descendant forms of spliting.]

• Determine how many persons there are in your master data base ( File / Properties ).
• Make a second copy of the master data base ( File / Save As / "workname" / Save ) to make a working data base and open it ( File / Open / "workname" / OK ).
• Pick a family record in the working data base that has one parent to be split.  This should be a family unit that is a good place to break off the portion of relatives desired.  If you are looking for ancestors only or descendants only, this process will be dramatically simple, but usually you want all relations of the selected individual (parents, children, ancestors, and descendants).
• Note all family member numbers ( RIN ) and marriage numbers ( MRIN ) as well as marriage details and sources.
• Break marriage ( Edit / Marriage / Delete ).
• Prepare to export a partial GEDCOM file ( File / Export . . . / Partial / Select ).
• Clear all previously selected (tagged) persons ( All / Clear ).
• Pick any individual that is in the new split group ( highlight by RIN or name ).
• Select all related persons ( All Related / Select ).   Note the number of persons selected.
• If the number of persons selected is the same as the number of persons in the master data base, there is another marriage to break.   Repeat the above from "Pick a ".  This marriage will sometimes be difficult to find.
• If the number of persons is not within the desired range, delete the working data base ( File / Delete . . . / "workname" /   Delete / Yes ), and try again using the master data base to create a new working data base.
• Continue the partial export process ( OK / Export . .  / "namepartial" / Export ) using an appropriate name.
• Begin a new data base ( "namepartial" ) using the just exported GEDCOM as input ( File / New / "namepartial" / Save / File / Import . . . / "namepartial" / Import ).
• Return to the master data base and export the family(s) that were broken ( File / Export . . . / Partial / Select / All / Clear ), select either parent of the broken family ( highlight by RIN or name ) , select family members ( Family / Select / As a parent with spouse . . . / OK / OK ), and export the family to a temporary ( "tempname" ) GEDCOM file ( Export . . . / "tempname" / Export ).
• Open the new "namepartial" data base ( File / Open / "namepartial" / OK ) and import the "tempname" GEDCOM ( File / Import . . . / "tempname" / Import ).
• Use the merge feature of your software to combine duplicate entries of the family ( Tools / Match/Merge . . . ) using the noted RIN above as your initial find.
• Delete the "workname" file ( File / Delete . . . / "workname" /  Delete / Yes ).
• Once satisfied that the "namepartial" file contains the appropriate individuals, families, notes, sources, and media references, return to the master data base file and trim the excess persons.  It would be appropriate to make another "workname" file ( File / Save As / "workname" / Save ) and open it ( File / Open / "workname" / OK ).
• Break the links of individuals to the previously selected target family(s) ( children, parents, . . . ) leaving only the common couple so that a note or link can be used to reference between data bases.
• Prepare to export a partial GEDCOM file ( File / Export . . . / Partial / Select ).
• Clear all previously selected (tagged) persons ( All / Clear ).
• Pick any individual that is in the master group ( highlight by RIN or name ).
• Select all related persons ( All Related / Select ).   Note the number of persons selected.
• If the number of persons selected is the same as the number of persons in the master data base, there is another marriage to break.   Repeat the above from "Break the ".
• If the number is within 2 times the number of broken families of the original master number less the number in the "namepartial" file, then continue the export.
• Continue the partial export process ( OK / Export . .  / "namemaster" / Export ) using an appropriate name.
• Begin a new data base ( "namemaster" ) using the just exported GEDCOM as input ( File / New / "namemaster" / Save / File / Import . . . / "namemaster" / Import ).
• Once satisfied that the new "namemaster" file contains the appropriate individuals, families, notes, sources, and media references, delete the original master data base  ( File / Delete . . . / "originalname" /  Delete / Yes ).  You may want to wait several weeks / months before doing this step to be certain that no data was lost, but be sure to do all of your updates to your new data bases.

Congratulations on performing major data base surgery.  You will be pleased with the results and the process can be reversed at any time.  I use a variation of the process to prepare GEDCOM files for specific interest groups and reports, but leave the master data base in tact and make all updates to the master data base only.

Obviously, this process is not to be interrupted with other activities, so plan on at least an hour of uninterrupted quiet to be sure that it is done without flaw.

You may want to use the Reorder program on GEDCOM files made from your new data bases to place the families in a logical order.  Creating a new data base from this reordered GEDCOM will help organize your postings and reports.  You may want to use the Report program to prepare a narrative report of ALL vital information in your data base (not just ancestor or descendant).