Hi all!

I am trying to create an database for relation between parents and
their children. I started with these Entities:

Parent
Child
Parent_Child (parent_id fk, child_id fk)

But this will only show relation between one parent and one child, so
I thought I could set up the Entity Parents to manifest the relation
between 2 parents. It's here my theory gets little rusty.

When I model this I struggle to see that it's correct

Parents Entity (Example):
parents_id (PK)
parent_id (FK)
parent_id (FK)

The second problem I struggle with is that a parent could have
children with more than one other parent. This I don't quite get a
grip of.

So if somebody have some pointers for I will appreciate it

On Sat, 05 May 2007 06:30:05 -0700, dnomade wrote:

Your initial table set-up, with one minor change, will suffice.

The change is to use as the primary key for your Parent-Child table the
combination of parent-id and child-id. This will permit you to quickly
access all of the children of any parent. (If you are using an RDBMS
that doesn't require tables to have primary keys -- no changes are required.)

This will also solve your second problem -- but retrieval will be
slow since the entire Parent-Child table will have to be searched to find
all of the parents of a child. If performance is an issue you can add a
secondary index on child-id.

HTH
Jerry-the-bookkeeper

On 5 Mai, 16:33, Jerry Gitomer <jgito... (AT) verizon (DOT) net> wrote:
Thank you for your response

I will see into the suggestion.

Thank you again

David

<dnomade (AT) gmail (DOT) com> wrote

First off, should you have an entity called "persons"? Can't a person be a
parent and also a child (of a different person, of course).

On May 5, 11:26 pm, "David Cressey" <cresse... (AT) verizon (DOT) net> wrote:

David Cressey:
How will this help?

I can't see that this will help to fin the relation between a parent
and the other parents he/she has children with. Could you please
explain it for me please

Thanks in advanced
David

On May 7, 6:24 pm, dNomade <dnom... (AT) gmail (DOT) com> wrote:

To clarify, in its simplest form you could use a structure like this:

relationships(name*,parent*)
* = (compound) PRIMARY KEY

To obtain a list of all the people with whom a given individual has co-
authored children:

SELECT r2.* FROM relationships r1
JOIN relationships r2 ON r2.name = r1.name
WHERE r1.parent = 'john lennon'
AND r2.parent <> 'john lennon';

result:

name________parent
julian lennon__cynthia lennon
sean lennon__yoko ono lennon

dnomade (AT) gmail (DOT) com wrote:
to decide what kind of business rules you are going to have in these
relationships. However, in this day and age many things are confused.
Even in Genealogy a person can only have 2 parents. Adults however can
have many children with sometimes with a legal spouse and sometimes with
multiple partners not married. When you think of a birth certificate,
you have to look at the elements on the certificate; Location, Date,
time, Father Mother.

People are born
People may be married
People have Parents
People have children

These kind of relationships can be very complicated.