Introduction to XML for Analysis (XMLA)

XML for Analysis (XMLA) is a SOAP-based, XML-only protocol that enables client applications to communicate with OLAP (Online Analytical Processing) and data mining services. It provides a standard way to send commands and receive results from Analysis Services.

XMLA is the primary interface for interacting with SQL Server Analysis Services (SSAS), allowing for a wide range of operations from data manipulation to metadata management.

XMLA Overview

XMLA acts as a bridge between client applications and the Analysis Services engine. It defines a structured format for requests and responses, ensuring interoperability across different platforms and development tools.

Key aspects of XMLA include:

  • Standardization: Based on XML and SOAP, providing a widely adopted communication standard.
  • Versatility: Supports both data and metadata operations.
  • Extensibility: Allows for custom commands and extensions.
  • Protocol Independence: Can be transmitted over HTTP/HTTPS.

XMLA Architecture

The XMLA architecture involves client applications sending XMLA requests to the Analysis Services server, which then processes these requests and returns XMLA responses. This communication typically occurs over HTTP or HTTPS.

The flow is generally:

  1. Client constructs an XMLA message (request).
  2. Request is sent to the Analysis Services instance via HTTP/HTTPS.
  3. Analysis Services parses the XMLA request.
  4. Analysis Services performs the requested operation.
  5. Analysis Services constructs an XMLA message (response).
  6. Response is sent back to the client.

Key Components of XMLA

XMLA messages are structured around specific elements:

  • <Command>: Contains the specific command to be executed. This can be an MDX, DMX, or XMLA-specific command.
  • <Parameters>: Used to pass parameter values for commands.
  • <DataSourceInfo>: Specifies connection information for the data source.
  • <PropertyList>: Contains a set of properties that control the behavior of a command or the execution context.
  • <Execute>: The root element for a request message.
  • <Results>: The root element for a response message.

Common XMLA Operations

XMLA supports a variety of operations, including:

Discover Operations

These operations retrieve metadata from Analysis Services. Examples include:

  • DISCOVER_DATASOURCE: Retrieves information about data sources.
  • DISCOVER_CATALOGS: Retrieves a list of available databases (catalogs).
  • DISCOVER_CUBES: Retrieves information about cubes within a database.
  • DISCOVER_DIMENSIONS: Retrieves information about dimensions.
  • DISCOVER_HIERARCHIES: Retrieves information about hierarchies.

Execute Operations

These operations execute commands that manipulate data or perform queries.

  • MDX (Multidimensional Expressions): Used for querying cube data.
  • DMX (Data Mining Extensions): Used for querying and manipulating data mining models.
  • DML (Data Manipulation Language): Used for loading and processing data within Analysis Services.
Tip: MDX and DMX queries are embedded within the <Command> element of an XMLA <Execute> request.

Example of a simple MDX query within an XMLA Execute request:


<?xml version="1.0" encoding="utf-8"?>
<Execute xmlns="urn:schemas-microsoft-com:xml-analysis">
  <Command>
    <Statement>
      SELECT {[Measures].[Internet Sales Amount]} ON COLUMNS,
             {[Date].[Calendar Year].Members} ON ROWS
      FROM [Adventure Works DW2019]
    </Statement>
  </Command>
  <PropertyList>
    <DataSourceInfo>Provider=MSOLAP;Data Source=localhost;Initial Catalog=AdventureWorksDW2019;</DataSourceInfo>
    <Format>Tabular</Format>
  </PropertyList>
</Execute>

Usage Scenarios

XMLA is fundamental for various Analysis Services tasks:

  • Business Intelligence Tools: Power BI, Excel, and other BI platforms use XMLA to connect to and query SSAS data.
  • Custom Applications: Developers can build custom client applications that leverage XMLA for programmatic access.
  • Data Integration: Tools like SQL Server Integration Services (SSIS) can use XMLA tasks for managing and processing Analysis Services objects.
  • Scripting and Automation: XMLA scripts can be used for deploying, migrating, and managing SSAS solutions.

Getting Started with XMLA

To start using XMLA, you typically need:

  • An instance of SQL Server Analysis Services.
  • A client tool or development environment capable of sending HTTP requests.
  • Understanding of XML, SOAP, MDX, and/or DMX.

Common libraries and SDKs exist in various programming languages (e.g., .NET, Java) to simplify XMLA communication.