Power Pivot Principles: The A to Z of DAX Functions – INFO.ALTERNATEOFDEFINITIONS

In our long-established Power Pivot Principles articles, we continue our series on the A to Z of Data Analysis eXpression (DAX) functions.  This week, we look at INFO.ALTERNATEOFDEFINITIONS. 

The INFO.ALTERNATEOFDEFINITIONSfunction

Dynamic Management Views (DMVs) are specialised queries provided by SQL Server Analysis Services (SSAS), Azure Analysis Services (AAS), and Power BI that offer an administrative view into the internal state of these systems.  DMVs are used to retrieve metadata, monitor health and performance, and diagnose problems within the database or data model.  They serve as a powerful tool for administrators and developers to gain insights into the workings of the database engine and the tabular data model, covering aspects like performance metrics, configuration settings, and the structure of database objects.

The $System schema DMVs in SQL Server Analysis Services (SSAS), Azure Analysis Services (AAS), and Power BI are categorised into four [4] types, each serving specific purposes:

• DISCOVER: requires admin privileges and provides information about the model, including details on connected sessions and environment configuration
• DMSCHEMA: focused on data mining, offering insights for predictive analytics and pattern recognition, mainly used in SSAS/AAS
• MDSCHEMA: targets multidimensional models, delivering metadata and structure from an MDX perspective, relevant for OLAP cubes and dimensions
• TMSCHEMA: designed for tabular models, it provides detailed metadata about tables, columns, measures, etc., using Tabular Model Scripting Language (TMSL) information, crucial for Power BI and tabular SSAS/AAS models.

In the past, if we want to query those $System schema DMVs we use external tool like Tabular Editors or DAX Studio to query them:

Now, we just need to write a simple DAX syntax to query those TMSCHEMA directly in DAX query View.  In this instance, we are using INFO.ALTERNATEOFDEFINITIONS function to query the TMSCHEMA_ALTERNATE_OF_DEFINITIONS. 

The INFO.ALTERNATEOFDEFINITIONS function is one of the system functions.  It employs the following syntax:

This function has no parameters.

Here are a few remarks about function come with INFO prefix:

• it is used for querying the DMV (Dynamic Management Views) from the $System schema called TMSCHEMA where TM stand for ‘Tabular model’ and TMSCHEMA provides information from the tabular model
• sometimes querying DMVs may fail if we do not have the appropriate permission.

We can write this INFO.ALTERNATEOFDEFINITIONS function on DAX Query View to get information on the TMSCHEMA_ALTERNATE_OF_DEFINITIONS:

It will query the $SYSTEM.TMSCHEMA_ALTERNATE_OF_DEFINITIONS and return an entire table with five [5] columns:

• ID
• ColumnID
• BaseColumnID
• BaseTableID
• Summarization.

Currently, there appears to neither be documentation for this TMSCHEMA_ALTERNATE_OF_DEFINITIONS nor INFO.ALTERNATEOFDEFINITIONS.

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