According to CIO.com, "Pivot tables are perhaps one of the most popular methods for analyzing data and business trends" and pivot tables / OLAP analysis are 1 of the 5 essential elements every BI solution should include: http://advice.cio.com/mrc/13181/5_essential_elements_every_business_intelligence_solution_should_include  To support Excel Pivot Tables, a data source must support ODBO (OLE DB for OLAP) and the MDX query language.  All of the major data source support this including Microsoft Analysis Services, Oracle OLAP, SAP BW, and Teradata BIO (Business Intelligence Optimizer).  Adding MDX query language support for any analytical data source is not an easy thing to do.  Not only do you have to follow the published specifications – http://www.xmla.org/xmla1.1.doc and http://msdn.microsoft.com/en-us/library/ms717005(v=VS.85).aspx, but you also need to follow the unpublished changes since the specs were last updated like understanding MDX 2005 and you also need to understand how MDX compliant apps like Excel Pivot Tables will connect to your OLAP data source.  This is not a trivial task – sometimes likened to building an RDBMS from scratch.  There is an easier way.  Dave Parsons, formely SVP Product Development of ALG Software (acquired by Business Objects which was then acquired by SAP) talks about how he and his team went about enabling Excel Pivot Tables connectivity for their Activity Based Costing product: http://www.simba.com/case-study-ALG-Software-MDX-Engine-ODBO-Interface.htm.