Microsoft SQL Server Analysis Services (SSAS[1]) is an online analytical processing (OLAP) and data mining tool in Microsoft SQL Server. SSAS is used as a tool by organizations to analyze and make sense of information possibly spread out across multiple databases, or in disparate tables or files. Microsoft has included a number of services in SQL Server related to business intelligence and data warehousing. These services include Integration Services, Reporting Services and Analysis Services. Analysis Services includes a group of OLAP and data mining capabilities and comes in two flavors multidimensional and tabular, where the difference between the two is how the data is presented.[citation needed] In a tabular model, the information is arranged in two-dimensional tables which can thus be more readable for a human. A multidimensional model can contain information with many degrees of freedom, and must be unfolded to increase readability by a human.[citation needed]
In 1996, Microsoft began its foray into the OLAP Server business by acquiring the OLAP software technology from Canada-based Panorama Software.[2]
Just over two years later, in 1998, Microsoft released OLAP Services as part of SQL Server 7. OLAP Services supported MOLAP, ROLAP, and HOLAP architectures, and it used OLE DB for OLAP as the client access API and MDX as a query language. It could work in client-server mode or offline mode with local cube files.[3]
In 2000, Microsoft released Analysis Services 2000. It was renamed from "OLAP Services" due to the inclusion of data mining services. Analysis Services 2000 was considered an evolutionary release, since it was built on the same architecture as OLAP Services and was therefore backward compatible with it. Major improvements included more flexibility in dimension design through support of parent child dimensions, changing dimensions, and virtual dimensions. Another feature was a greatly enhanced calculation engine with support for unary operators, custom rollups, and cell calculations. Other features were dimension security, distinct count, connectivity over HTTP, session cubes, grouping levels, and many others.[4]
In 2005, Microsoft released the next generation of OLAP and data mining technology as Analysis Services 2005. It maintained backward compatibility on the API level: although applications written with OLE DB for OLAP and MDX continued to work, the architecture of the product was completely different. The major change came to the model in the form of UDM - Unified Dimensional Model.[5][clarification needed]
Microsoft Analysis Services takes a neutral position in the MOLAP vs. ROLAP arguments among OLAP products.
It allows all the flavors of MOLAP, ROLAP and HOLAP to be used within the same model.
MOLAP - Multidimensional OLAP - Both fact data and aggregations are processed, stored, and indexed using a special format optimized for multidimensional data.
ROLAP - Relational OLAP - Both fact data and aggregations remain in the relational data source, eliminating the need for special processing.
HOLAP - Hybrid OLAP - This mode uses the relational data source to store the fact data, but pre-processes aggregations and indexes, storing these in a special format, optimized for multidimensional data.
DDL in Analysis Services is XML based and supports commands such as <Create>, <Alter>, <Delete>, and <Process>.
For data mining models import and export, it also supports PMML.
