Webtrends Analytics 9 Adminstration Guide, November 2012
When you enable Visitor History in a profile, Webtrends creates a Visitor History database that stores data about the behavior of each unique visitor analyzed for the profile. Using a strong session tracking method such as cookies, Webtrends identifies visitors and updates the Visitor History database each time they visit.
You configure the profile to collect the type of visitor data you want to include in reports, and Webtrends generates visitor history query parameters that track the visitor behavior you specified. Webtrends uses the visitor history query parameters to identify and store unique visitor data in the profile’s Visitor History database. For example, when you enable campaign history tracking, Webtrends identifies ads that visitors view using the ad (WT.mc_id) query parameter. To track campaign history, Webtrends generates the most recent campaign (WT.vr.rac_x) query parameters and uses these parameters to store each visitor’s campaign activity throughout their visitor lifetime. During the first visit that a visitor views an ad, Webtrends stores data for the first ad they viewed. Each time the visitor views another ad, Webtrends updates the visitor's most recent ad viewed data and maintains this data for each reporting time period. You can create custom reports that use the generated visitor history parameters to understand visitor behavior with advertisements over time.