The proposed framework of the library recommender system includes implementation of three agent viz. profile agent, content based agent, and collaborative agent. One of the important tasks performed by profile agent is the identification of subject area/s of user. The implementation of this part is focused in this paper. This work uses n-Gram and Jaccard's similarity. The ACM's Computing Classification System is used as knowledgebase. This is required to be used while deciding in which subject area/s the particular user may have interests. This work is essential to be performed in implementation of library recommender system. The output of this work is used by the library recommender agent (content based and collaborative). The results are evaluated using precision, recall, and F-1 measure. Comparison with similar work identified during literature study is done. It is found that n-Gram and Jaccard's similarity are useful and gives better performance for the particular task implemented in profile agent.