Introduction to MDX - Professional SQL Server Analysis Services 2005 with MDX - page 100

The members in the date dimension of the three tuples above are different
and therefore these tuples refer to different cells. As per the definition of a set,
a collection of these tuples is a valid set and is shown here
{ ([Date].[Calendar Time].[2004].[H1 CY 2004].[Q1 CY
2004], [Product].[Product Line].[Mountain],
[Customer].[Country].[Australia]), ([Product].[Product
Line].[Mountain], [Customer].[Country].[Australia],
([Date].[Calendar].[2003].[H1 CY 2003].[Q1 CY
2003]),([Customer].[Country].[Australia],
[Date].[Calendar].[2002].[H1 CY 2002].[Q1 CY 2002],
[Product].[Product Line].[Mountain] )}
A set can contain zero, one, or more tuples. A set with zero tuples is referred
to as an empty set. An empty set is represented as
{ }
A set can contain duplicate tuples. An example of such a set is
{Customer.Country.Australia,
Customer.Country.Canada, Customer.Country.Austrailia}
This set contains two instances of the tuple Customer.Country.Australia. Be-
cause a member from a dimension by itself forms a tuple, it can be used in
MDX queries. If there is a tuple that is specified by only one dimension, you
do not need the parentheses to specify the cell. Similarly, when there is a
single tuple specified in the query you do not need curly braces. When an
MDX query is being executed, implicitly this tuple is converted to a set in the
query rather than representing the object as a tuple.
Now that you have learned the key concepts that will help you to understand
MDX better, the following section dives right into the MDX query syntax, the
operators used in an MDX query or an MDX expression.