OLAP is the acronym for On – Line Analytical Processing . It is a solution used in the field of Business Intelligence ( Business Intelligence ), which consists of queries to multidimensional structures (or OLAP Cubes ) that contain summarized data from large Databases or Transactional Systems ( OLTP ). It is used in business reports for sales, marketing, management reports, data mining, and similar areas.
The reason for using OLAP for queries is speed of response. A relational database stores entities in discrete tables if they have been normalized. This structure is good in an OLTP system but for complex multi-table queries it is relatively slow. A better model for searching, but worse from an operational point of view, is a multidimensional database. The main feature that enhances OLAP is that it is the fastest when making selects, as opposed to OLTP, which is the best option for INSERTS, UPDATES AND DELETES.
There are some classifications among OLAP implementations. The classification is made based on what type of engine the data is stored in:
ROLAP is an OLAP implementation that stores data in a relational engine. Typically, the data is detailed, avoiding aggregations, and the tables are normalized. The most common schemes used are star or snowflake, although it is possible to work on any relational database. The architecture is made up of a relational database server and the OLAP engine is located on a dedicated server. The main advantage of this architecture is that it allows the analysis of a huge amount of data.
MOLAP is an OLAP implementation that stores data in a multidimensional database. To optimize response times, summary information is usually calculated in advance. These precalculated values or aggregations are the basis for the performance gains of this system. Some systems use data compression techniques to decrease disk storage space due to precomputed values.
HOLAP (Hybrid OLAP) stores some data in a relational engine and some in a multidimensional database
DOLAP is a desktop oriented OLAP (Desktop OLAP). It fetches all the information you need to analyze from the relational database and saves it to your desktop. From that moment on, all queries and analyzes are done against the data stored on the desktop.