"All we want are the facts ma'am." -Sgt. Joe Friday

A fact is the fundamental unit of information used by the Family module. It represents a single line in a GEDCOM file which contains

1. Depth indicator (DI) of a fact in a fact hierarchy (0 - n)
2. A fact code (think of it as a class name)
3. fact value (the actual data).

The one exception to this format is a "root" fact (explained below) which stores an xref value between the depth indicator and the fact code and has no fact value. The family module maintains the general idea but with a significant change. Instead of the 0 - n DI the module uses a relationship table to track which facts relate to each other. The module also add a field to link facts with their node (if one exists) and another to store an xref¹.

GEDCOM Example:
0 @1@ INDI
1 NAME John C. /Doe/
1 BIRT
2 DATE Jan 1870
2 PLAC Durham, Durham, North Carolina
2 SOUR @S2@
3 NOTE month and year listed on census form
1 DEAT
2 DATE 31 Dec 1907
2 PLAC Hillsborough, Orange, North Carolina

Family Module Tables:
family_facts

family_relations

It may be best to think of this as a tree structure. ² The individual node (fid 1) is a "root" fact or "root node" because it had a GEDCOM level of 0 meaning that it has no parent. This root node has 3 child nodes: fid 2 (NAME), fid 3 (BIRT), & fid 6 (DEAT). The name node (fid 2) simply stores a value. The birth (fid 3) and death (fid 6) nodes have additional children instead of values. ³ Each root node also has an xref value so that other trees can point to this node (fact 1 has the xref "1" in the example above). No child nodes can have an xref value although a child node may store an xref pointer to a root node in its value field (fact 6 points to the fact with an S2 xref in the example above).