RFC: How to decide which backend(s) to use

[Jussi Kukkonen]

This RFC is actually somewhat related to the earlier (hopefully even
ongoing) discussion on interfaces.


Selecting the backend to use is not just a matter of choosing the
default one, if we want to do it right. Example: Let's say the user has
the following position backends installed
   1. GPS
   2. Hostip

Scenario 1. Application wants to know the city/country (assume civic
            location is now included in the position-interface).
Scenario 2: An application wants coordinates. User does not have a GPS
            device with her (or she is indoors).

In both scenarios the default GPS backend is unusable. Problem in
scenario 1 is something that could be avoided with having separate
interfaces for civic/coordinate location, but that is just a special
case. Scenario 2, and many other situations like it, would require the
application to call get_all_position_providers() and try another backend
if the current_position()-method of the first backend failed... This is
not friendly at all.


Conclusions/questions:

* There should be an order of preference for backends
  (a list in gconf instead of just the default backend?)

* Getting information from the several backends should be as seamless as
  possible. I don't see why we couldn't totally abstract this in the
  bindings / wrapper library?
     If a method (e.g. current_position()) fails, and
     if no backend was initialized with generic init-method and
     if there are backends still left on the list of backends
          Initialize the next backend in the list and
          call the current_position method() on the new backend

Is there something seriously wrong with this idea? If it works,
applications could just say
"I want [Coordinates|City Name|Street Address|...]"
and get that information without knowing any details.


  -jussi

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