Hi I would like to know in which db and table the datas for sharepoint calendar ? I need to have a reading access to these datas with another application write in php.
Don't access the data directly in the SharePoint database. The database structure is difficult to workout and also Microsoft will not support your SharePoint environment if you are reading data straight out the database!
As TZHX says use the Web Services or even better use the REST interface or the Client Side Object Model instead. They have been built for the reason that you require.
More information can be found here:-
Client Side Object Model = http://msdn.microsoft.com/en-us/library/ee537247(v=office.14).aspx
The calendars are stored as a List in SharePoint, and so the data will be in the Content Database for the Web Application, in the
Moral of the story, better to use web services than to try and parse these databaess yourself.