Expose a computed field (or external data) to Views I want to add a virtual field to a "node", its content should be computed  from other fields of this node (with the module of the same name or with a hook) AND it must be usable by Views filter and sorting. 

Is this possible (using modules or PHP code) ?
I found answser on this site:
http://barcelona2012.drupaldays.org/sessions/displaying-external-data-fly-views-and-ctools

This simple module give a clear example on how to expose external data (webservice) to a views.