OLAP is a data structure that provides multidimensional cubes from data and provides useful information for decision makers. While designing an OLAP system, the most important factor is reporting requirements. Compared to OnLine Transactional Processing (OLTP), OLAP provides faster reports because it reshapes data in cube structures rather than the traditional relational structure based on tables.

As an example, assume that you want to create a report in a BI system for sales based on products and dates. You might need to get the sales amount per day, per month, or per year. You might also have categories of products. So, it will be helpful if you have a graph with two dimensions, Product as one dimension and Date as another dimension:

Having two dimensions helps to achieve each granular point and each conjunction of both dimensions easier and faster. For example, point A shows the total sales amount of ProductA in August 2012. Each point in the preceding graph is a measure...