The primary reference for the Latent Dirichlet Allocation (LDA) is the following. The first five pages (Pg nos. 993-997) describes the model and the plate notation. David M. Blei, Andrew Y. Ng, Michael I. Jordan ; Latent Dirichlet Allocation. Journal of Machine Learning Research (JMLR); 3(Jan):993-1022, 2003. http://www.jmlr.org/papers/volume3/blei03a/blei03a.pdf

Also see the following Wikipedia pages on:

• Latent Dirichlet Allocation: https://en.wikipedia.org/wiki/Latent_Dirichlet_allocation

• Description of the plate notation: https://en.wikipedia.org/wiki/Plate_notation

WordNet based similarity measures in NLTK: http://www.nltk.org/howto/wordnet.html