http://www.academia.edu/8339332/An_Efficient_Indexing_and_Searching_Technique_for_Information_Retrieval_for_Urdu_Language
http://www.cle.org.pk/Publication/papers/2014/CLE%20Urdu%20Books%20N-grams.pdf
https://www.researchgate.net/publication/283045451_Keyword_based_Information_Retrieval_System_for_Urdu_Document_Images
Related: Word Spotting based Retrieval of Urdu Handwritten Documents
http://www.aclweb.org/anthology/W11-3605