Every day Internet sites collect and store lots of user data. For effective usage of that data, special tools are required. Online Analytical Processing (OLAP) tools are suggested for that purpose. Usage of these tools is related to usage of Data Warehousing tools. Therefore issues of Data Warehouse design, data transformation and transferring to data warehouses were discussed. In the present years there are new trends in business computer systems industry – WEB Data Warehouses. New characteristics of such systems were analyzed. OLAP tools usage is not possible without multidimensional data model. Main entities and operations with these entities were reviewed and mathematical definitions given. Data transformation process was proposed. This process flow shows how transformations can be used for transferring data from WEB site to multidimensional database. OLAP tools of Microsoft SQL server and Oracle database server (the most popular database management systems in Lithuania) were analyzed in experimental part of work. Data transformation and reviewing in desktop applications, WEB systems and office applications tools were compared and recommendations given.