PgSQL and integration between 2 PHP programs and a Java program

Hi,

I'm a newby so please bare with me :

I want to integrate 2 PHP scripts and a Java program that all have the
capability of using PgSQL as their databases.
The point is that all the programs have their own DB and table structure.
What I want to do is to have a single DB for all of them and have them
authenticate the users somehow that a registered user in PHP script can
login to Java program too!
suppose that PHP1 scripts have a table called members with 2 fields
"username" and "password". PHP2 has its own table called logins and have 2
fields "login_name" & "login_password". and my Java program have a table
called profiles with "plogin" and "ppass". suppose that the password field
in all the programs are MD5. Now I want to integrate them. I have read some
PgSQL help books and it seems that there are many options that PgSQL offers
for this, like inheritance, views and join. but I don't know exactly what to
do. Can anyone help please?

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Warm Regards,
Amir