Question: Setup:  

One table called `documents` with columns `author_id` and `reviewer_id` (among others).  

One table called `users` with column `user_id`.

I need to create two referential integrity links:  

One-to-many between `user_id` and `author_id`.  

One-to-many between `user_id` and `reviewer_id`.

In other words, these two columns in `documents` are independent of one another, but both should have a value that is a valid `user_id`.

Adding either one of these relationships works fine. When I try to add a second relationship in the `Edit Relationships` window, Access complains with the following message:

*Microsoft Office Access can't enforce referential integrity for this relationship.*

I've searched, but couldn't find any solutions to this. Any ideas on how this relationship could be configured?

Answer: 
To add two individual relationships from one table to two different fields in another, you need to have multiple instances of the parent table in the relationship window.

So, you'd add your Users and Documents table to the relationships window and create the first relationship. Then add the Users table to the relationship window a second time (it will be aliased as Users\_1), and then add the second relationship from this aliased copy. 

This is completely consistent with the same way you'd define two such joins in the QBE, so I'd say it's not problematic at all. But it's not necessarily obvious!
This is not a direct answer to your question, but if I were you I would use another data model to implement the complex many-to-many relation between `Documents` and `Users` by creating a third table called `DocumentsUsers` with the following fields:

```
PK  documentUser_id (*)
FK  document_id
FK  user_id
    documentUser_type

(*) or you could alternatively use document_id + user_id as a PK... 

```

The documentUser\_type field will hold the relation type, ie 'user', 'reviewer', etc. By using this model, you could have, for the same book, multiple users and/or multiple reviewer, which might be closer to reality. You could even have other relation types like 'author', etc.