A mashup is "a web application that combines data from more than one source into a single integrated tool; an example is the use of cartographic data from Google Maps to add location information to real estate data, thereby creating a new and distinct web service that was not originally provided by either source" (Wikipedia). For a terrific example of a mashup, see EveryBlock Chicago. Mashup editors allow you to create a mashup without being a programming whiz (although some technical knowledge is useful).
Graphs, Maps, Trees: Abstract Models for a Literary History (Google Books), Franco Moretti. Published 2005.