SSAS 2012 supports three different approaches for creating a BISM (Business Intelligence Semantic Model):
1. Tabular
a. Uses relational modelling constructs like such as tables and relationships
b. Uses xVelocity in-memory analytics engine for sorting and data calculations
c. Needs to use SSDT (SQL Server Data Tools) to implement
d. Can import data from relational data sources using OLE DB native and managed providers
e. Tabular solutions only support one model.bim file per solution, which means that all work must be done in a single file. Development teams that are accustomed to working with multiple projects in a single solution might need to revise how they work when building a shared tabular solution.
f. support DAX calculations, DAX queries, and MDX queries
g. Tabular model databases can use row-level security, using role-based permissions in Analysis Services (DAX implementation required)
h. It might be not a good choice for the systems that are going to load terabytes of data