CUBE DESIGN BY HANNES MEYER

OnLine Analytical Processing OLAP

Agenda

  What are cubes?   Multidimensionality   Storage of multidimensional data.   Hierarchies   Operations   Demo

What are cubes?

  Multi-dimensional representation of data

What are cubes (cont.)?

  syn: Hypercube, multidimensional database (MDB), olap cube

  Cubes can have more than three dimensions

Fact Tables

  Contain numerical measurements of a certain business process.  E.g. $12.000 sales in NY store on 12-01-08

  Additionally foreign keys to different dimension tables  E.g. further store/sales person information

  Center in star schema

Dimension Tables

  Contain attributes by which data can be grouped   e.g. city/region of store, product category   Linked to the fact table via their primary keys   Slowly changing dimensions: dimensions which

change over time. Can be dealt with in 3 ways:  Overwriting old values  Add new row to table, distinguish records by versioning  Add new column (attribute) to existing row

Data Storage Models

  relational databases (ROLAP)  Data in tables  Summaries stored in precalculated tables

  multi-dimensional databases (MOLAP)  Data in multidimensional arrays  + Less disk space  + Better Performance (precalculated aggregates)   - Time to aggregate & calculate   - Updates require recalculation

  Hybrid (HOLAP)

Hierarchies

  Grouping of dimensions   e.g. month -> semester -

> quartal -> year   2008

 H1 2008   Q1 2008

  Jan 2008   Feb 2008   March 2008

  Q2 2008 …  H2 2008 …

  e.g. country -> sales region -> state -> city -> store

  Germany   Southern germany

  BaWue   Stuttgart

  Store A   Store B

  Bavaria   Munich

  Store A B C

Operations: Slice

  Slicing is the process of retrieving a block of data from a cube by filtering on one dimension

Operations: Dice

  Dicingis the process of retrieving a block of data from a cube by filtering on all dimensions

Operations: Drill Up/ Down

  Drilling up: Presenting data at a higher level on the hierarchy e.g. Store -> Region

  Drilling Down: Presenting data at a lower level on the hierarchy Region -> Store

Building the cube in SSAS

  Preconditions  Connecting datasources  Defining views  Selecting dimensions

  Define fact & dimension tables & time dimension   Select measures   Deploy & query the cube   Demo