Ivan explained tracker upstream is using ontologies a lot. In fact, they chosen Nepomuk, as it’s the ontology used in KDE and also Gnome community agree with using it too. These kind of ontologies help to understand concepts and properties applications are using, avoiding misunderstandings.
Right now MAFW is using properties like ‘Artist’, ‘Album’ or ‘Title’, but as many other applications it is not using neither Nepomuk nor other ontology at all. So I wonder if it would be helpful (or unnecessary at all) moving to Nepomuk, so at the end instead of using ‘Artist’ string, it would use the corresponding Nepomuk property.