I have been using an Excel file to handle the administration of a repository management system, with hundreds of entries going into the Excel sheet and being read from the sheet by management scripts. I know what it does to the performance of your application.
My word of advice on this: even though it is technically possible to access an Excel file directly to retrieve the data, I would steer clear of that option. The problem is that you create an enormous overhead for each single read operation on a cell in Excel (an ActiveX or other object must be created that can do almost anything you would ever want to do, including frying some eggs for breakfast).
I don't think you can use ActiveX (or COM) objects with FrameMaker's ExtendScript. If so, I would like to know how. I agree with Jang, though. It is pretty easy to parse through a CSV file with ExtendScript.
FrameScript is much better with ActiveX objects. I have a bunch of FrameScript scripts that read and write to Excel spreadsheets.
you are right you don't have such features as ActiveX or COM-Integration with ExtendScript. If you want to have this, you have to use FDK or FrameScript.
But I found a possibility on how you can get such a connection via external objects. You will find an example here:
C:\Programme\Adobe\Adobe ExtendScript Toolkit CC\SDK\Samples\cpp
I think Russ already implemented such a connect in the past. But I think it's a little bit tricky.
If I have to do such things out from excel I work with Excel XML Calculation Tables (2003) format.Then I use XML Objects of ExtendScript. But it get's a little bit tricky due to that multiple namespaces in the Excel XML format.
In most cases CSV would be the best and easiest way.
Hope this helps