Do levels have members or is it just hierarchies?

Question

can someone definitively tell me why

[Dimension].[Hierarchy].[Level].&[(Unknown)] doesn't make sense

while

[Dimension].[Hierarchy].[Level].&[some_other_member] does

and yet both [Dimension].[Hierarchy].&[(Unknown)] and [Dimension].[Hierarchy].&[some_other_member]

both do

To me isn't unknown simply the case where the data doesn't fall into a defined hierarchy member?

this area of SSAS seems a bit opaque to me.

Any link to the official definition would be great.

Answer 1

Each member is at one level of a hierarchy. If you have a standard attribute hierarchy, then you have two levels: The All level containing the All member and the level named like the hierarchy, which contains all the members found in the attribute column of the relational dimension table as well as the Unknown member. The latter is contained on that level, as it is clearly not part of the All level, and it is included in the sum of all members of its level to give the numbers for the All member.

The official documentation of the UnknownMember function describes what I described above and some special cases like the case that an attribute hierarchy has set the IsAggregatable property to false (i. e. the All level is missing, an the level named like the attribute is to only one, end hence the top level).