At the core of the Analysis Services engine is the ability to model various complex business problems using calculations. In older versions of Analysis Services, calculations were based on dimensions such that each dimension typically contained one or more multilevel hierarchies. Starting with Analysis Services 2005, the calculation model changed due to the introduction of a new multidimensional approach that combined the traditional OLAP and relational worlds. That combination leveraged the Unified Dimensional Model through attribute hierarchies (which are entities within a dimension). Attributes and relationships between attributes form the basis of the new calculation model. Hierarchies (attribute or multilevel) are the way of navigating the dimensional space. Attribute hierarchies typically have two levels, the optional "All" level and another level that contains all the members of the attribute. Hence, cells in the cube space can be accessed directly through the attribute hierarchies or multilevel hierarchies. Though most of the calculation definitions for a cube are defined within the MDX Script, some calculations are specified as properties of dimension attributes. Even while defining security for various hierarchies within a dimension, you specify the security restrictions through the attribute hierarchies of the dimension. Hence, attributes form the fundamental building blocks for all calculations in Analysis Services 2008.