You can build such app with Appery.io, as I mentioned above you can build anything browser supports, anything PhoneGap support. In case you're not sure if your DB exposed via REST API I need you to provide more details on your DB (example of request and response from DB).
what else do you need to know about the db? WHat would you need from the host company that houses the database. They are Nexternal.com and use nexternal.net..
The database/software is capable of responding to xml requests. Does, is that compatible with exposing the data via REST API?
Nexternal.com doesn't have REST API.
does that mean I won't be able to use your service to building the app?
That means you won't be able to use Nexternal.com to build your app with Appery.io. You can try to import DB data into Appery.io DB in CSV or JSON format, but I'm not sure if it's possible in your case with Nexternal.com
the database in an Nexternal is Microsoft SQL
The main idea is that DB needs to have REST API so that you can send requests and get response back. If you can send some request to any URL with request parameters and get in responce json/xml with data that you can use later to form page content then you can use it, but Nexternal doesn't have REST API...
We would recommend you to look at restxpress.com -- it allows to expose relational data as REST APIs.
How do you know for sure that nexternal does not use or have REST API? According to Nexternal REST API just defines a set of functions to which the developers can perform requests and receive responses. The API for this within Nexternal is the XML documentation
If Nextternal does have a REST API -- it's good. Then you can use the API when you build an app in Appery.io.