PowerPivot: Data Analysis Expressions (DAX) Language
The Data Analysis Expressions (DAX) language is a new formula language that allows users to define custom calculations in PowerPivot tables (calculated columns) and in Excel PivotTables (measures). DAX includes some of the functions that are used in Excel formulas, and additional functions that are designed to work with relational data and perform dynamic aggregation.
The syntax of DAX formulas is very similar to that of Excel formulas, using a combination of functions, operators, and values. Where DAX formulas differ from Excel formulas is that DAX functions work with tables and columns, not ranges, and let you do sophisticated lookups to related values and related tables. With DAX formulas, you can create aggregations that would ordinarily require in-depth knowledge of relational database schemas or OLAP concepts. Moreover, because calculations in DAX formulas utilize the highly optimized in-memory engine, you can rapidly look up and calculate values across very large columns or tables.