I'm working on a content compiler that will take my raw input assets and convert them into resources for loading into my engine. The actual conversion is easy and I've already got it working fine. The problem is that one input file (a PSD image for example) can produce multiple output files (each layer of the PSD as a separate DDS texture if that option is enabled). This part is working fine too, but I need to figure out how to clean the resources up when the input file is deleted. I don't want to have to re build all the assets every time a file is deleted/renamed/whatever. I just want to be able to delete the multiple outputs from the one asset file, and rebuild that single file. How would you recommend going about tracking the outputs? I already have a metadata file for per-asset options, but using that to track outputs seems like it would be fragile to any changes made in Windows Explorer while the content compiler wasn't running.