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

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.ATTRIBUTEHIERARCHIES. 

The INFO.ATTRIBUTEHIERARCHIES function

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 wanted to query those $System schema DMVs, we would use external tools like Tabular Editor or DAX Studio to query them:

Now, we just need to write a simple DAX syntax-based formula to query these TMSCHEMA directly in DAX query view.  In this instance, we are using INFO.ATTRIBUTEHIERARCHIES function to query the TMSCHEMA_ATTRIBUTE_HIERARCHIES. 

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

This function has no parameters.

Based upon the ‘[MS-SSAS-T]: SQL Server Analysis Services Tabular Protocol’ from Microsoft (which you may access here), the AttributeHierarchy object represents the attribute hierarchy of a column in a table.  It is an optional child object of a Column object and is implicitly created by the server.  When the attribute hierarchy is present, the column becomes available as a hierarchy and can be queried by using the MDX language.

We can write this INFO.ATTRIBUTEHIERARCHIES function in DAX query view to obtain the same information on the TMSCHEMA_ATTRIBUTE_HIERARCHIES:

It will query the $SYSTEM.TMSCHEMA_ATTRIBUTE_HIERARCHIES and return an entire table with six [6] columns:

• ID: this represents a reference to the object
• ColumnID: this is an ID_based reference to a Column object
• State: this is a value that provides information about the state of the AttributeHierarchy object.  The possible values are as follows:
  • Ready (1): the Attribute Hierarchy is able to be queried and has up-to-date data
  • NoData (3): not applicable to Attribute Hierarchies
  • CalculationNeeded (4): the Attribute Hierarchy does not contain any data because it was not refreshed.  There is no error associated with the Attribute Hierarchy
  • SemanticError (5): not applicable to Attribute Hierarchies
  • EvaluationError (6): not applicable to Attribute Hierarchies
  • DependencyError (7): the column that is associated with this Attribute Hierarchy is in an error state (SemanticError, EvaluationError or DependencyError)
  • Incomplete (8): not applicable to Attribute Hierarchies
  • SyntaxError (9): not applicable to Attribute Hierarchies.

• AttributeHierarchyStorageID: an ID-based reference to an AttributeHierarchyStorage object.  The AttributeHierarchyStorage object is reserved for internal use only
• ModifiedTime: this is the time that the object was last modified
• RefreshedTime: this is the time that the object was last refreshed.

It should be noted that:

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

Come back next week for our next post on Power Pivot in the Blog section.  In the meantime, please remember we have training in Power Pivot which you can find out more about here.  If you wish to catch up on past articles in the meantime, you can find all of our Past Power Pivot blogs here.