Their software uses log file analysis and page tagging. Log analysis reads the files in which the web server records all its transactions. Via page tagging, parameter name–value pairs are appended (either automatically by a JavaScript "tag" or manual hand-coding) to the query string of a gif image which resides on a data collection server. When a visitor loads the page in a browser, the browser sends a request to the data collection server so that it may load the gif image. The data collection server receives the request and logs the parameters included in the query string of the gif image.
