We have a sharepoint based application that uses a custom database for storing metadata/files (which could also be on a file share)

My question is how can the standard file checkin/check out option in document library be customized?

The javascript file ows.js in the layouts folder contains the functions that provide checkin/check out/ open file functionality. Behind the scenes it relies on a combination of HTTP Post/GET methods + SOAP + an activeX control to achieve the desired functionality.

Customizing these javascript function seems tedious/error prone.

Note that we have a web service that exposes endpoints, for retrieving necessary file information/data from the backend. The difficulty is in integrating it with the sharepoint js functions, due to lack of proper documentation. (Also the js functions might change over different versions of sharepoint)

Also is it possible to create files/open files etc from the cache area on the client machine from server side code?