In the data source properties window you can view connection properties for a data source and also change how queries are generated against the target cube.
To open the properties window for a data source, click on a data source in the data sources window and then press the 
button.
The properties window has two tabs, connection and query.
Connection
In the connection tab you can view the connection details for this data source. These are the settings that were specified when creating a new report/data source. See the DWE Administrators Guide for more information on the connection properties.
Query
You can change the type of MDX generated against the server here. Note that DataWarehouse Explorer in most cases generates optimal MDX by itself, but there can be cases in which you would like to tweak the generated MDX to perform better. The following options are available:
Allow NonEmptyCrossjoin |
When this option is enabled, the query is allowed to use the NonEmptyCrossjoin function. This function can improve performance dramatically, but can produce false results in some cases. On by default. Supported on SSAS 2000 only. |
Filter axes by measure |
When set, empty items on the axes will be filtered using the NonEmpty MDX function, based on the current measure. Setting this option can provide a performance boost when dealing with calculated members in sparse hierarchies. Off by default. Supported on SSAS 2005 only. |
Sub-select is non-visual |
When set, sub-select slicing will be performed on non-visual subcubes and visual totals will not be automatically applied. When this option is not set, sub-select slicing will be performed on a visual subcube, thus automatically enforcing visual totals. Search for NON VISUAL in the SELECT documentation page for more information. Off by default. Supported on SSAS 2008 and higher. In SSAS 2005 the sub-select is always visual. |
Use sub-select for slicer |
When set, the query will express the whole slicer (i.e. background selection) as a sub-select clause. If not set, the slicer will be expressed using a WHERE clause where possible. Off by default. Supported on SSAS 2005 and higher. |