Dimensions

Dimensions Overview

A dimension table is normally defined, for our purposes, as a table that allows us to constrain queries on the fact table.

A dimension is built from the Data Warehouse connection. Unless you are doing a retro-fit of an existing system, dimensions are typically built from one or more load tables.

The normal steps for creating a dimension are defined below and are covered in this chapter. The steps are:

 Identify the source transactional data that will constitute the dimension. If the data is sourced from multiple tables ascertain if a join between the source tables is possible, or if a series of lookups would be a better option.

 Using the 'drag and drop' functionality drag the load table that is the primary source of information for the dimension into a dimension target. See Building a Dimension (on page 284).

 If only one table is being sourced and most of the columns are to be used (or if prototyping) you can select the auto create option to build and load the dimension and skip the next 4 steps. See Building a Dimension (on page 284).

 Add columns from other load tables if required. See Building a Dimension (on page 284).

 Create the dimension table in the database. See Building a Dimension (on page 284).

 Build the update procedure. See Generating the Dimension Update Procedure (on page 293).

 Run the update procedure and analyze the results. See Dimension Initial Build (on page 308).

Modify the update procedure as required. See Dimension Initial Build (on page 308).