Along with the development of ICT (Information and Communications Technology) and popularization of mobile devices, the information environment of our society has radically changed. As a result, the library's role model also needs to be changed. It is necessary to develop new information services as of e-library at the same time to enrich the currently providing services. Among the various types of e-library services, the most important ones are those of personalized services reflecting the patron's profile such as his/her interest knowledge fields, knowledge level, preferences, etc. The approach we take as the first step toward this direction is to analyze the loan records of library for extracting the patron's interest area information as a profile, and then we understand what the patrons want. We define the interest area based on the decimal classification (DC) categories and use the ratios of books borrowed in these categories as the patron's interest area profile. In this paper, we investigate the correlations of DC categories, and we redefine the profile of a patron so that to understand his/her profile more exactly. The studies in this direction are considered to be useful in developing better elibrary services.