Figure 5: shows the session length distribution for the NASA dataset after the session is identified. The vertical axis stands for the percentage of occurrence of the number of session length. The horizontal axis is marked with the length of session. The figure shows, for each session length, the statistical distribution of the session having that many consecutive requests on the server. As a session becomes longer, the percentage of web sessions decreases dramatically. The short session take a large proportion of the whole data set. This chart shows that significant numbers of sessions only consist of one or two request and there are not too many web user sessions which extend over 10 visits thus the average session length is rather low.