Why is OLAP valuable?
OLAP is valuable because of its flexibility. Once the facts and dimensions are defined within the OLAP server, OLAP tools provide an easy way to analyze data by simply dragging and dropping dimensions and facts into the appropriate locations.
Anyone who's ever tried to develop a cross-tab report will appreciate the simplicity of being able to drag the dimensions and facts into position. If you've never developed a cross-tab report, please note that it is not an easy task. Typically, a substantial amount of time is spent trying to figure out how to make the data convert into the rows and columns. The problem is that every change to the report requires a great deal of effort to execute. In contrast, with OLAP it's as simple as dragging a new dimension in place and removing existing dimensions.
Making the cross-tab report easier is certainly valuable, but it is not an end unto itself. The desired end result is to help transform data into information. It just so happens that many people approach the process of understanding their data as the development of cross-tab reports.
OLAP is useful in helping to determine why the data appears the way it does. For instance, if the sales for North America are way up or way down for a given quarter, it's easy to expand the North American geography into the states to see which state or states may be responsible for the difference.
By progressively expanding portions of levels within a dimension, it is possible to drill-down into progressively more detail, but only the detail that is necessary to spot a trend or a problem.
OLAP tools also allow a breakdown structure of the data where you start with a single piece of data and you dissect it into a series of levels looking at the data for something interesting. For instance, let's say that we're looking at a total sales number for the month of June. Breaking down this number might first occur by country as a member of the geography dimension. In seeing a larger than expected number for North America, you might choose to break the number down into product lines. From the product lines breakdown you may notice that your gold plated widget sales were up substantially. You decide to look at the sales by state so you select the gold plated widget product line and expand the state level of the geography hierarchy. Each level in the breakdown tells you more details about what makes up the number you're interested in.
