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: 
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.
First, I suggest you change you columns' names to `author_user_id` and `reviewer_user_id` respectively, to make it clear that each reference `user_id`.

Second, you should be aware that use of Access's UI tools are not compulsory. Many of us find them unintuitive but happily there are alternatives. One is to use SQL DDL e.g. [ANSI-92 Query Mode](http://office.microsoft.com/en-gb/access/HP030704831033.aspx):

```
ALTER TABLE Documents ADD 
   CONSTRAINT fk__ document_author_user_id__Users
   FOREIGN KEY (author_user_id)
   REFERENCES Users (user_id)
   ON DELETE NO ACTION
   ON UPDATE NO ACTION
;

ALTER TABLE Documents ADD 
   CONSTRAINT fk__ reviewer_user_id__Users
   FOREIGN KEY (reviewer_user_id)
   REFERENCES Users (user_id)
   ON DELETE NO ACTION
   ON UPDATE NO ACTION
;

```

Third, consider you may need a `CHECK` constraint (or Table[sic] Validation Rule) to ensure a user cannot review their own work e.g. 

```
ALTER TABLE Documents ADD 
   CONSTRAINT document_author_cannot_review_their_own_work
   CHECK (author_user_id <> reviewer_user_id)
;

```