Online Analytical Processing (OLAP) Concepts

• Online Analytical Processing OLAP: is an approach to swiftly answer multi-dimensional analytical (MDA) queries.
• Broader category of business intelligence, which encompasses relational reporting and data mining.
• Databases configured for OLAP use a multidimensional data model, allowing complex analytical and ad-hoc queries with a rapid execution time.
• Ad-hoc ("for this"): allows users to create specific, customized queries.
• OLAP tools enable users to interactively analyze multidimensional data from multiple perspectives.
• The core of any OLAP system is an OLAP cube, which consists of numeric facts called measures  (derived from the record in the fact table) which are categorized by dimensions (derived from the dimension tables). The cube metadata is typically created from a star-schema or snowflake schema of tables in a relational database.
• Consists of 3 analytical operations: consolidation, drill-down, slicing and dicing.
• Consolidation: involves the aggregation of data that can be accumulated and coputed in one or more dimensions. i.e. all sales offices are rolled up to the Sales Department.
• Drill-Down: allows users to navigate through the details.
• Slicing and dicing: feature whereby users can take out (slicing) a specific set of data of the cube and view (dicing) the slices from different viewpoints.
• Multidimensional (MOLAP): is the classic form of OLAP and is sometimes referred to as just OLAP.
• Stores data in an optimized multi-dimensional array storage, rather than in a relational database.
• Requires the pre-computation and storage of information in the cube - the operation known as processing.
• Relational (ROLAP): works directly with relational databases. The base data and the dimension tables are stored as relational tables and new tables are created to hold the aggregated information.
• Each action of slicing and dicing is equivalent to adding a "WHERE" clause in the SQL statement.
• Hybrid (HOLAP): there's no clear agreement that constitutes HOLAP, except that a database will divide data between relational and specialized storages.
• i.e. some vendors, a HOLAP database will use relational tables to hold the larger quantities of detailed data, and use specialized storage for at least some aspects of the smaller quntities of more aggregate or less-detailed data.
• Other types of OLAP:
• WOLAP: Web-based OLAP
• DOLAP: Desktop OLAP
• RTOLAP: Real-Time OLAP

• Top Vendors:
• Microsoft Corp.
• Oracle - Hyperion Solutions Corp.
• IBM - Cognos
• Business Objects
• MicroStrategy
• SAP AG
• Applix
• Infor