As discussed in section 2.2, analysis of how users are accessing a site is critical for determining effective marketing strategies and optimizing the logical structure of the Web site. Because of many unique characteristics of the client-server model in the World Wide Web, including differences between the physical topology of Web repositories and user access paths, and the difficulty in identification of unique users as well as user sessions or transactions, it is necessary to develop a new framework to enable the mining process. Specifically, there are a number of issues in pre-processing data for mining that must be addressed before the mining algorithms can be run. These include developing a model of access log data, developing techniques to clean/filter the raw data to eliminate outliers and/or irrelevant items, grouping individual page accesses into semantic units (i.e. transactions), integration of various data sources such as user registration information, and specializing generic data mining algorithms to take advantage of the specific nature of access log data.