Build properties

Here it is !

The underlying wiring is done: process -> data -> db.

I don't have data endpoint yet, it should make the subject of another PR I believe, That one is already big enough ...
If I remember correctly, the default encoding depends on the locale settings.  So the same string can work and can fail depending on what external locale is used.

I believe elsewhere we expect non-unicode strings to be in 'utf-8', so I'd expect an explicit conversion from that.