How can I compare an address to a database to see if it has been entered before?

At work we have a web service with an oracle database that contains a list of addresses.  I need to create a simple form to see if a specific address exists in the database.  Return a message that if it does exist it does not qualify or that if it does not exist in the database it does qualify.  Can we use web services with JotForm?

Unfortunately, that is not possible. 

I can only suggest you to import your addresses as submission to your form and then to use the Unique Question feature to prevent duplicate submissions with the same address. 

Import App: Easily Import Your Excel or CSV Data into JotForm

How to set Form Limits Based on a Unique Question

Another option would be to set a condition for each address and to show a custom message using a text field if the address already exists. 

How to Show or Hide Fields Base on User's Answer