About the Series ...
This
article is a member of the series Introduction to MSSQL Server 2000
Analysis Services. The series is designed to provide hands-on
application of the fundamentals of MS SQL Server 2000 Analysis Services,
with each installment progressively adding features and techniques designed to
meet specific real-world needs. For more information on the series, as well as
the hardware / software requirements to prepare for the exercises we
will undertake, please see my initial article, Creating Our First Cube.
Note: Service Pack 3 / 3a updates are assumed for MSSQL Server 2000, MSSQL
Server 2000 Analysis Services, and the related Books Online
and Samples. Images are from a Windows 2003 Server
environment, upon which I have also implemented MS Office 2003, but the
steps performed in the articles, together with the views that result, will be
quite similar within any environment that supports MSSQL Server 2000 and MSSQL Server 2000 Analysis Services ("Analysis
Services" or "MSAS"). The same is generally true,
except where differences are specifically noted, when MS Office 2000 and
above are used in the environment, in cases where MS Office components are
presented in the article.
Overview
In
dealing with MSAS implementations on a daily basis, and especially when being
called upon to tune MSAS implementations performed by others, I come across the
less-than-optimal use of calculated members quite often. As most of us
know, calculated members are dimensions or measures (depending
upon the designated parent dimension) that are constructed, using a formula,
from other dimensions or measures in our cubes. A typical example of a calculated
member that is designed for a measure, to which we will refer in this article
as a calculated measure, is a Profit calculated measure that is
created by subtracting a cost / expense measure from a sales /
revenue measure. Another common calculated measure is a variance
measure, which is created by taking a difference between an actual and a
budgeted value (or similar kinds of values), among other approaches.
If the calculation /
formula that we use in creating the calculated measure consists of a simple
match between two measures, we can often use a derived measure instead.
In this article, we will discuss the advantages and disadvantages involved, and
compare and contrast the methods of adding these sorts of measures to our
cubes. In examining the use of derived
measures to enhance cube response times, we will:
-
Discuss the
drawbacks in using calculated members in cases where a derived measure might be
substituted;
-
Discuss
benefits and disadvantages that might accrue through the use of derived
measures;
-
Describe an
illustrative scenario, upon which we will determine that a derived measure can
offer a tuning solution for a group of hypothetical information consumers;
-
Implement a
simple solution through creation of a derived measure to replace an existing calculated
measure;
-
Explain the
results we obtain from the steps we take to accomplish the solution.
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