I was delighted, recently, to come across Steve Pepper's
'Ontopia' website, and especially the demos of his Omnigator
browser for topic maps. The richest of the demos is about
Italian opera [demo] and this sub-list of resource-types
especially caught my fancy: article, A-Z Opera synopsis, bio,
born, description, died, editorial guidelines, gallery, home
page, illustration, libretto, Opera News synopsis, poster,
premiere, revision, sound clip, synopsis, web site.