SQL Server Analysis Services Understanding Unified Dimension Model (UDM)

Agenda » Introduction to UDM » Dimension model core components » Dimension model example » Dimension tables » Star and Snowflake schemas » Cubes » Cube storage » UDM Components » UDM Overview

Introduction to UDM » The SSAS mission is to break out of the OLAP space by unifying the relational and dimensional reporting models using UDM.

Dimension model core components » Measures - represent the numerical values (facts) that are used to measure business activity. » Dimensions - the main goal of the dimensional model is to allow users to slice and dice data using different perspectives called dimensions. » Dimension hierarchies - to facilitate drilling through data, dimensions may have hierarchies. » Dimension members - the actual dimension entities that belong to each level are called dimension members.

Dimension model example

Dimension tables » Dimension data are stored in relational tables called dimension tables. ‣ usually wide (have many columns) but don’t have many rows ‣ large number of columns is required to accommodate various dimension-related attributes » The classic dimensional model defines two types of relational schemas that describe the relationship between the dimension and fact tables: ‣ Star schemas ‣ Snowflake schemas

Star and Snowflake schemas » A star schema requires that a dimension hierarchy be contained within a single table. This requires the dimensionaltable to be denormalized. » If the dimension hierarchy is left normalized, then the schema is of a snowflake type schema.

Cubes » The Cube is logical storage object in SSAS. » Cube combines dimensions and measurements to provide fast multidimensional access to cube data.

Cube storage » Stores all fact rows and have aggregated values for each cell » Cube aggregation options ‣ ROLAP - the fact data and aggregations will be kept in the relational database. ‣ MOLAP - the fact data and aggregations will be kept in the cube ‣ HOLAP - the fact data and aggregations will be kept in the relational database and cube. » SSAS usually uses MOLAP cubes. » MOLAP storage option requires cube processing.

UDM Components » Data source view (DSV) - logical data schema that seeks to present the data from the relational datastore in a standard and intuitive way. » Dimensional model – cubes » Calculations - business logic. » End-user model - provides intuitive end-user reporting and data navigation experience. (reports, KPI) » Management settings - cube configurations to meet various operational requirements, including availability, latency, and security

UDM Components

UDM Overview » UDM goal to unite the best of both worlds (relational and dimensional) and become a bridge between the users and data.