Logical Functions: IsAncestor(): Conditional Logic within Calculations
February 5, 2007
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.
In this lesson, we will expose another logical function which we can use for testing a member or level at which a cell is being calculated, the IsAncestor() function. The general purpose of IsAncestor() is 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.)
The IsAncestor() function, like other logical functions and operators, evaluates values and returns a Boolean value. The utility of IsAncestor() becomes clear when we realize the capability that it gives us to determine the position, together with the relationship to progenitors, of a member within a dimensional hierarchy. IsAncestor() more specifically allows us to test whether a member is an ancestor of another member that we specify within the dimension to which it belongs.
Similar to IsLeaf(), IsSibling(), IsChild(), IsGeneration(), and other MDX functions, IsAncestor() can best be employed to apply conditional logic within a couple of primary ways: as a component within a calculation, and as a component within a filter expression. In this article, we will concentrate upon IsAncestor() from the perspective of its use within a calculation. We will discuss the straightforward purpose of the function, to ascertain (and indicate) whether a member is the ancestor of another specified member; the manner in which IsAncestor() manages to do this; and ways we can leverage the function to support effective conditional logic to meet various business needs within our own environments.
Along with an introduction to the IsAncestor() function, this lesson will include:
The IsAncestor() Function
According to the Books Online, 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 (to which I will refer as the primary member expression throughout this article) is an ancestor of the second specified member (the secondary member expression); 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 simple, hypothetical business needs that illustrate a use for the function. This will afford us an opportunity to explore some the basic options that IsAncestor() can offer the knowledgeable user. 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.
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 in an attempt to use it in standalone fashion.
Lets look at syntax specifics to further clarify the operation of IsAncestor() .
Syntactically, we employ the IsAncestor() function by specifying 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:
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, in the parentheses to the right of the function. As an example, 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:
Each of the listed members is a descendant of South Australia in the cube, as shown in Illustration 1.
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.