Logical Functions: IsAncestor(): Conditional Logic within Filter Expressions

About the Series …

This article is a member of the series, MDX Essentials.
The series is designed to provide hands-on application of the fundamentals of
the Multidimensional Expressions (MDX) language, with each tutorial
progressively adding features designed to meet specific real-world needs.

For more information about the series in general, as well as
the software and systems requirements for getting the most out of the lessons
included, please see my first article, MDX at First Glance: Introduction to MDX Essentials.

Note: Current updates are assumed for MSSQL
Server
, MSSQL Server Analysis Services, and the related Books
Online
and Samples.

Overview

In IsAncestor():
Conditional Logic within Calculations
, another article
within my MDX Essentials
series, we introduced the IsAncestor() function from the perspective of
its use within a calculation. We discussed the straightforward purpose of this
logical function, to return whether or not a specified member is an
ancestor of another member we specify
(By “ancestor,” of course, we mean a
member from which the specified member is descended within a dimensional
hierarchy.) We discussed the manner in which IsAncestor() manages to do
this, and ways we can leverage the operator to support effective conditional
logic
to meet various business needs within our own environments.

In
this article, we will examine IsAncestor(),
once again as a
conditional logic modifier, but within the context of a filter.
Combining IsAncestor() with the MDX Filter()
function is another way we commonly see it in action in the business
environment, and our exposure to the practical aspects of its employment in
this way will serve to round out our overall awareness of the potential of IsAncestor(). From the perspective of the use
of the IsAncestor()
function in combination with Filter(),
this article will include:

  • A review of the general syntax surrounding the function;

  • Illustrative examples of uses of the function in practice
    exercises;

  • A brief discussion of the MDX results obtained within each of the
    practice examples.

The IsAncestor() Function

Introduction

As we related in IsAncestor():
Conditional Logic within Calculations
, the Books
Online
tell us that the IsAncestor() function “returns whether a
specified member is an ancestor of another specified member.” A Boolean value of “True” is returned if
the member expression to which the function is applied is an ancestor of
the second specified member; otherwise IsAncestor() returns “False.” In its capacity, as a logical function, to “test”
the nature / status of a member, IsAncestor() is often employed in
conjunction with the IIF() function to conditionally drive the return of
data, such as a member or members, or values, based upon the relationship between
members as ancestor / descendant.

We will examine in detail the
syntax for the IsAncestor() function after our customary overview in the
Discussion
section that follows. Following that, we will conduct
practice examples within a couple of scenarios constructed to support
hypothetical business needs that illustrate uses for the function. This will
afford us an opportunity to explore some the basic options that IsAncestor()
can offer the knowledgeable user. Our current examination will focus upon
the use of IsAncestor() within the context of a filter. Hands-on practice with IsAncestor(),
where we will create queries that employ the function, will help us to activate
what we have learned in the Discussion and Syntax
sections.

NOTE:
For more detail surrounding the Filter() function, see Basic
Set Functions: The Filter() Function
, a member of my Database Journal MDX Essentials
series.

Discussion

To restate our initial description
of its operation, IsAncestor() returns “True” if a specified
member expression represents an ancestor of another member (that is,
lies between the secondary member and the top / “All”
dimensional level
) that we specify within a given use of the function;
otherwise, the function returns “False.” We can use IsAncestor() to
apply conditional logic, based upon the location and / or existence of
members. As we have noted to be the case with most MDX functions, pairing IsAncestor()
with other MDX functions can help us to leverage its power much further
than we might do in an attempt to use it in standalone fashion.

Let’s look at syntax specifics to further clarify the
operation of IsAncestor() .

Syntax

To review the syntax involved
with employing the IsAncestor() function, we specify the primary
member expression
(the member which we are testing as to “ancestor status”)
and the secondary member expression (the member in relation to which
we are testing the primary member expression) within parentheses to the
immediate right of the function. The function takes the member expressions
thus appended to it as its arguments, and returns True if the member
denoted by the primary member expression is an ancestor of
the secondary member expression (or, in other words, if the primary
member
lies somewhere between the secondary member and the “top” of
the dimensional hierarchy).

If the member specified by the primary
member expression
is not an ancestor of the secondary
member
(or if the primary member and the secondary member belong
to different dimensions) a False is returned, as we might expect.

The general syntax is shown in
the following string:

IsAncestor(Primary_Member_Expression, Secondary_Member_Expression)

Employing IsAncestor(), like
most of the MDX logical functions, is, in the mechanical sense,
straightforward. As we have noted, we simply place the primary and secondary
member expressions
, respectively, within the parentheses to the right of
the function. To use the example from our syntax discussion in IsAncestor(): Conditional Logic within Calculations, within a query executed against the sample Adventure
Works
cube, for the dimension named Geography (with a hierarchy of
the same name), the following pseudo-expression,

IsAncestor([Geography].[Geography].[State-Province].[South Australia],
      [Geography].[Geography].CurrentMember) 

returns True for the current
member
of the Geography dimension / Geography hierarchy for
each of the following:

  • Cloverdale

    • 6105
  • Findon

    • 5023
  • Perth

    • 6006

Each of the listed members is a descendant of South
Australia
in the cube, as shown in Illustration 1.



Illustration 1: Descendants of South Australia …

Depending upon the structure of the query (and specifically
upon whether the syntax defining axes, etc., eliminates nulls), if members of
other dimensions, or members of levels higher than South Australia
within the Geography hierarchy, were returned in, say, the row axis of
the dataset, their values would be null.

NOTE: For
information on several of the “relative” functions, of which .CurrentMember
is an example, see my article MDX
Member Functions: "Relative" Member Functions
,
within the Database Journal MDX
Essentials
series.

We will practice some uses of the IsAncestor() function
in the section that follows.

William Pearson
William Pearson
Bill has been working with computers since before becoming a "big eight" CPA, after which he carried his growing information systems knowledge into management accounting, internal auditing, and various capacities of controllership. Bill entered the world of databases and financial systems when he became a consultant for CODA-Financials, a U.K. - based software company that hired only CPA's as application consultants to implement and maintain its integrated financial database - one of the most conceptually powerful, even in his current assessment, to have emerged. At CODA Bill deployed financial databases and business intelligence systems for many global clients. Working with SQL Server, Oracle, Sybase and Informix, and focusing on MSSQL Server, Bill created Island Technologies Inc. in 1997, and has developed a large and diverse customer base over the years since. Bill's background as a CPA, Internal Auditor and Management Accountant enable him to provide value to clients as a liaison between Accounting / Finance and Information Services. Moreover, as a Certified Information Technology Professional (CITP) - a Certified Public Accountant recognized for his or her unique ability to provide business insight by leveraging knowledge of information relationships and supporting technologies - Bill offers his clients the CPA's perspective and ability to understand the complicated business implications and risks associated with technology. From this perspective, he helps them to effectively manage information while ensuring the data's reliability, security, accessibility and relevance. Bill has implemented enterprise business intelligence systems over the years for many Fortune 500 companies, focusing his practice (since the advent of MSSQL Server 2000) upon the integrated Microsoft business intelligence solution. He leverages his years of experience with other enterprise OLAP and reporting applications (Cognos, Business Objects, Crystal, and others) in regular conversions of these once-dominant applications to the Microsoft BI stack. Bill believes it is easier to teach technical skills to people with non-technical training than vice-versa, and he constantly seeks ways to graft new technology into the Accounting and Finance arenas. Bill was awarded Microsoft SQL Server MVP in 2009. Hobbies include advanced literature studies and occasional lectures, with recent concentration upon the works of William Faulkner, Henry James, Marcel Proust, James Joyce, Honoré de Balzac, and Charles Dickens. Other long-time interests have included the exploration of generative music sourced from database architecture.

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