Invalid objects

If I perform the query  

select owner||'.'||object_name, object_type from dba_objects where status = 'INVALID';  

I find a number of procedures, packages, package bodies and views are listed.  

What would cause an object to become invalid and what are the implcations for the application?  

Margaret Received on Wed Oct 20 1999 - 09:09:32 CDT