Thanks for your reply.
I find that "individuals" and "companies" each have attributes that
are completely irrelevant to the other. E.g. "individuals" have sex
and language (so e-mail can be sent to them as "Dear Sir" or "Dear
Madam" in both English and Spanish). The only time they have
information in common is when they are customers, where they have a
tax id, billing address, sales, etc.
By "company" I mean any juridical entity (I didn't use the
word "entity" in order not to confuse it with ERD entities). So
a "company" can have many "individuals" and an individual can also
have multiple "companies" (e.g. the firm he works for, a club, a
An "individual" can be of the subtype "personal_relation"
or "customer" but for some persons both types overlap (e.g. a
personal friend with whom I also do business).
I think that I cannot put 'customer' as the supertype because
many 'individuals' and 'companies' are not customers (I wish they
were :-)) so they wouldn't share the 'customer' attributes.
ATTEMPT: I thought of having an "individual_customer" and
an "company_customer" as subtypes of "individual" and "company",
But in your experience, wouldn't it be a mess to have half of the
customers in one entity and half in the other?