Another good place to begin your research is in reference resources, like the ones listed below. They can often provide useful background and genre information and they are a good place to corroborate data you may have found on the internet.
The Grove Music Online Grove Music Online is an integrated music resource on the web, including the full text of The New Grove Dictionary of Music and Musicians, The New Grove Dictionary of Opera and The New Grove Dictionary of Jazz.
This comprehensive, scholarly resource contains articles on many major Broadway composers and lyricists, such as Stephen Sondheim, Cole Porter, and the Gershwin brothers. It also contains extended articles on genres, including “musical,” “vaudeville,” and “operetta.” These articles provide excellent historic overviews and useful bibliographies.
The Oxford Companion to American Theater provides basic information on performers, composers, playwrights and others involved in American theater. There are also useful entries on individual musicals.