Database Reference
In-Depth Information
Since the same column is used as the key and the name of an attribute in many cases,
it's better to use the
HideMemberIf
options, which hide members when they have the
same name as their parent rather than blank names. Blank names could mean empty
strings are being used as keys, and this could in turn restrict your ability to build good
attribute relationships. For example, if you had two customers in different countries
but left both with empty strings for their
State
and
City
, the empty strings would be
interpreted as the same distinct member (with an empty string as the name and key)
which appeared under both countries. Therefore, you would be wrong to say there
were one-to-many relationships between
Country
and
State
, and
State
and
City
.
Using
HideMemberIf
on a ragged hierarchy also carries a query
performance penalty, although in general, it still performs better
than using a parent/child hierarchy.
Summary
In this chapter, we discussed how to deal with some common problems we
might face when designing our Analysis Services dimensions: grouping and
banding members and numeric values; slowly changing dimensions; junk
dimensions; ragged hierarchies; and parent/child hierarchies. We found that we
can create new attributes on a dimension to group members and create bandings
for numeric values using some simple SQL. This can have a positive impact on the
user's experience. We also found that with a bit of thought, the three different types
of SCDs can all be modeled satisfactorily. With ragged hierarchies, we learned that
the parent/child hierarchies are very flexible, but have several problems, especially
with query performance, and should be avoided where possible. We also saw that
using a regular user hierarchy and the
HideMemberIf
property is a better option,
although not without its own limitations.
In the next chapter, we will stay on the topic of modeling and look at how common
business requirements can be handled with measures and measure groups.
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