100% agree with this. Determining the "direction" of dependency like this is one of the main considerations around implementing something as a library or a ser

100% agree with this. Determining the "direction" of dependency like this is one of the main considerations around implementing something as a library or a service. I've built services that expose the latest/current version of an underlying library, with various versions of that library used in products across the company. There is also a question of overhead - calling a library is almost always SO much faster and lighter than calling out to some service, especially if we're talking JSON or XML over HTTP.