1. An apparatus for searching for personalized content based on a user's comment, the apparatus comprising: a computer system comprising a processor and a memory; a query receiving unit operating on the computer system and adapted to receive a user query from the user, the user query including one or more terms; a preference analyzing unit operating on the computer system and adapted to analyze the user's comment, wherein the user query and the user's comment are made by the same user and the user's comment is related to the user query, and the preference analyzing unit adapted to extract the user's preferred terms, and wherein the user's comment is the user's assessment of each piece of content; a query extending unit operating on the computer system and adapted to select at least one term from the extracted terms and to extend the user query by generating a query set which includes both the user query and the selected term, the query set including a plurality of terms used to request content from a database, the plurality of terms including both the one or more terms included in the user query and the selected term; and a content searching unit operating on the computer system and adapted to search for pieces of content based on the query set.
2. The apparatus of claim 1 , wherein the preference analyzing unit extracts the user's preferred terms related to the user query from information about the user's comment using a Term Frequency-Inverse Document Frequency (TF-IDF) technique.