[Routing] How to handle lack of connectivity within the routing graph?

[David MENTRE]

Hello,

While playing with routing is OSM map, I have observed that the OSM map
is not fully connected if you consider only the routable ways[1]. For
example, the map or Rennes city, France[2] appears to be made of 3335
ways divided into 8 different connected components.

With such a divided map, sometimes there is no route between two points
if those points are in two separated components.

Has anybody any idea how one should handle this?

 * Should I consider having a bug in my program? (not entirely excluded
   ;-) For example, a bad interpretation of way attributes;

 * Is this a "bug" in the OSM data (error made by people or lack of
   enough data)?

 * In the above case, are other routing programs (e.g. recently
   announced Gosmore) using some kind of "tricks" to join the separated
   components (e.g. consider two way points so close that they are the
   same point)?

Sincerely yours,
david

Footnotes: 
[1]  Ways with the "highway" attribute with following values:
       | Motorway
       | Motorway_link
       | Trunk
       | Trunk_link
       | Primary
       | Primary_link
       | Secondary
       | Tertiary
       | Unclassified
       | Track
       | Residential
       | Living_street
       | Service

[2]  http://www.openstreetmap.org/?lat=48.1157&lon=-1.6625&zoom=13&layers=B0FTT

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GPG/PGP key: A3AD7A2A David MENTRE <dmentre at linux-france.org>
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