The previous example has show, how data have to be collected with complex queries.

• The design of these can be very difficult. It can take a long time, until a query produces the right results.
• The execution of a query can be very time consuming, since the database engine has to search all of the implied tables several times for each of the selected datasets.

Experience shows, that the design of the queries is normally too difficult, since the complex model is difficult to understand. Thus skilled staff is needed in order to do the querying.

These observations show, that the relational model is not optimized for OLAP. OLAP needs a structure, which is more oriented at the structures of the desired output.