Mapping Document Types to Applications
The document type (MIME) database allows users to specify their preferred applications for opening different types of document. This is the mechanism by which Nautilus, Evolution and other applications decide which application to run when they encounter a document they cannot open themselves.
It is important for users to be able to double-click on documents they see on the desktop, such as files and email messages, and have them launch in their favorite application. Therefore, your GNOME application should associate itself at install-time with all the document types it can handle. Technical details on doing this can be found in the GnomeVFS API reference.