Simply put, Historiography is about writing history. Approaches to writing history have a history of their own.Thinking Medieval: An Introduction to the Study of the Middle Ages, by Marcus Bull, offers a readable overview of the field which is accessible online.
For quick identification of persons, places, events, and short descriptions, see:
The Oxford Dictionary of the Middle Ages is a recent (2010) electronic reference source that reflects recent scholarship on the Middle Ages including coverage of the world beyond Europe in the period such as Byzantium, Islam, Asia, and Africa. The Dictionary is part of Oxford Reference which includes a large number of other Oxford reference books. Searches can be restricted to the Dictionary of the Middle Ages, in the complete database, or limited by subject. Entries are signed, and many include brief bibliographies
Dictionary of the Middle Ages
The Dictionary of the Middle Ages (1982-1989) is an older print reference, Main Reference D114 .D5 1982, that is still useful.
Medieval Scandinavia (DL30 .M43 1993, request from Storage), Medieval England (Main Ref DA129 .M43 1998), Medieval France (Main Ref DC33.2 .M44 1995), Medieval Germany (Main Ref DD157 .M43 2001), Medieval Italy (Man Ref DG443 .M43 2004), and Medieval Iberia (Spain and Portugal; Main Ref DP99 .M335 2003) are a series of encyclopedias compiled by specialists in the medieval history of those countries. Entries include bibliographies of additional sources.