The Approach :- 
Establish the Business Rules or FACTS
The Facts define what is known about the 'Things of Interest' in the area being studied. 
They establish an English-language version of the relationships between the 'Things of Interest' 
which can be understood and agreed to by the key people such as Users. 
This is very useful when the 'Things' become Entities or Tables in the Database.

The purpose of defining the Facts is to establish common understanding and agreement of the important 
terms and concepts involved in Genealogy. 
I added some additional Facts after discussions with Rory on December 14th. 2007.
1. Families
An individual can be in zero or one Family.
In other words, an Individual may or may not be part of a Family, but cannot be in more 
than one Family at one time.

2. Relationships
Two Individuals can be in one and only one Relationship at any point in time.
In fact, my design allows for two people to be in more than one Relationship, but I can't think of 
any examples right now !
This is regardless of whether they are members of a Family.
For example, a Parent will always have a Parent/Child Relationship with their Children, even if the 
Parents get divorced.

A note on Families :-
The Model has to allow for the concept of a family. 
In other words, to define one family from another so that an individual can be a member of 
more than one family, for example, step parents. 

A. The Things of Interest are :- 
A.1 Individuals
A.2 Relationships

B. Business Rules :-
B.1 Every INDIVIDUAL can be involved in zero or many RELATIONSHIPS.
B.2 Each INDIVIDUAL plays a ROLE in a RELATIONSHIP.
B.3 Every RELATIONSHIP involves two INDIVIDUALS.

C. Valid Relationships are :-
C.1 Families
C.2 Marriages

The Data Model supports an infinite number of RELATIONSHIPS, 
which can be easily added to the RELATIONSHIPS Table as required.

D. Valid Roles are :-
C.1 Brother
C.2 Daughter
C.3 Father
C.4 Husband
C.5 Mother
C.6 Partner
C.7 Sister
C.8 Son
C.9 Wife

The Data Model supports an infinite number of ROLES, 
which can be easily added to the ROLES Table as required.