Array of documents in constant

A few followup questions occur to me, before discussing best ways to handle this.

1. What exactly is your need to store the document references (ids, etc) within a constant, specifically?
2. Does this constant really have to reflect *all* documents in a folder?  How does the particular folder come into play here? 
3. How many images will the total list likely be?  Just a handful, or hundreds, or something in between?
4. From where exactly will you derive the list of text labels used in the "category" dropdown?  Is the expectation that this will be stored like in a separate constant, or something else?

I'll try to explain my idea as good as I can (I'm fresh to Appian, so i probably won't be aiming for the best practice :) ).

I will have only handful of categories (these categories are just example, I would like to find the best practice for these "image from one component depends on text value from the other component" when it comes to less then 10 or 15 different values).

I believe that writing of the mapping rules "image for value" can't be avoided (or at least I can't see better practice at the moment).

So, when I have to modify expressions to map image on category, I would like to at least avoid manual addition of new images to the constant array if I can.

Let's say I have folder with 4 images at the moment (I believe array of image UUIDs would be the best choice because IDs may vary through the environments?) and expression for mapping these 4 images to 4 corresponding categories.

At some point I add 3 new images to the folder for category avatars.

Is there a way to write that constant so it can dynamically switch from 4 elements array to 7 elements array and then the only thing that remains for me is to define new rules for 3 new categories/images? Or I have to add 3 new image UUIDs manually to the array before that step?

I'll try to explain my idea as good as I can (I'm fresh to Appian, so i probably won't be aiming for the best practice :) ).

I will have only handful of categories (these categories are just example, I would like to find the best practice for these "image from one component depends on text value from the other component" when it comes to less then 10 or 15 different values).

I believe that writing of the mapping rules "image for value" can't be avoided (or at least I can't see better practice at the moment).

So, when I have to modify expressions to map image on category, I would like to at least avoid manual addition of new images to the constant array if I can.

Let's say I have folder with 4 images at the moment (I believe array of image UUIDs would be the best choice because IDs may vary through the environments?) and expression for mapping these 4 images to 4 corresponding categories.

At some point I add 3 new images to the folder for category avatars.

Is there a way to write that constant so it can dynamically switch from 4 elements array to 7 elements array and then the only thing that remains for me is to define new rules for 3 new categories/images? Or I have to add 3 new image UUIDs manually to the array before that step?

For the constant-based solution, I don't believe there's any easy way to work around the issue of having to update the constant to account for the added images.  I would almost suggest you instead consider using an expression rule where you feed in a folder ID and it spits out the list of files found within (see getdocumentsfromfolder() and similar OOB functions).

Thank you, Mike, for your analysis of my problem and your advices!