function.proto and yaml file extensions

[amirhormati]

Hi folks,
I have some naïve questions about how sunstrait is structured and is supposed to be used.

Looking at the simple YAML extensions, the first question that came to my mind was, for a new backend (e.g. BigQuery), should I be using these YAML files or should I be defining my own? I'm assuming defining my own is the way to go....but wanted to hear your thoughts. I looked at some other projects (for example ibis-substrait). It looks like they just dynamically initialize the extensions part of the plan in the beginning of their python code and don't use the YAML files.

Second, I'm looking at function.proto:

1- I'm trying to understand where it is used?
2- Why it is not the standard way to define functions and their signatures?

Thanks.