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

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.PERSPECTIVETABLES.

The INFO.PERSPECTIVETABLES 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 used external tools like Tabular Editors or DAX Studio to query them:

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

There are two [2] main arguments in this function (excluding numbering):

• RestrictionName: this argument is optional and repeatable this represents the restriction name
• RestrictionValue: this argument is optional and repeatable this represents the restriction value.

Based upon the ‘[MS-SSAS-T]: SQL Server Analysis Services Tabular Protocol’ from Microsoft (which you may access here), the PerspectiveTable object includes a Table object into the Perspective object. It is a child of a Perspective object. The child PerspectiveColumns, PerspectiveMeasures, and PerspectiveHierarchies objects allow customizing which parts of the Table are visible in the Perspective.

We can write this INFO.PERSPECTIVETABLES function on DAX query view to get the same information on the TMSCHEMA_PERSPECTIVE_TABLES:

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

• ID: this is a reference to the object
• PerspectiveID: this is an ID-based reference to Perspective.
• TableID: this is an ID-based reference to Table.
• IncludeAll: this is a Boolean that indicates whether all Column, Hierarchy, and Measure objects in the Table object are automatically added to the perspective. When "true", the objects are automatically added; otherwise, PerspectiveColumn, PerspectiveHierarchy, and PerspectiveMeasure need to be explicitly added to the PerspectiveTable.
• ModifiedTime: this is the time the object was last modified.

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 we 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.