Assigning Complex Categories to Contacts - very interesting question

Thanks in advance for your help on this dilemma! --

MY GOAL:

I am designing what should be a simple contacts database and we need to be able to assign contacts to multiple categories, such that:

1- users can continually add categories

2- users can change the name of categories (e.g. from "donor" to "giver") and have filemaker automatically update this name for all entries that have this category

3- Each contact can have many categories, and each category can have many contacts (obviously)

4- It is easy to get together a found set of records and quickly add them all to the same category.

THE PROBLEM:

I thought I would do this using 3 files - contacts.fp5, categories.fp5, and a bridge file, categoryassignments.fp5. Then I'd display and add the category assignments through a portal in the contacts file. BUT - with a large database, and if it is in a multi-user environment, wouldn't this take too long to search/sort etc. because it has to make the cross-file index... Also, to add large groups of records to a single category would take minutes because I'd have to create a record in the bridge file for each new assignment.

I know there is a solution out there, this can't be a one-of-a-kind dilemma. What tricks can I use?

Thank you so much!

Chris