SQL Server Analysis Services

XML for Analysis (XMLA) is a standard XML-based protocol for communicating with OLAP (Online Analytical Processing) data sources. It defines a set of XML elements and attributes that allow clients to send commands and receive results from OLAP servers, such as Microsoft SQL Server Analysis Services.

XMLA was developed to provide a vendor-neutral, interoperable way to interact with OLAP systems. Before XMLA, different OLAP vendors had proprietary APIs, making it difficult for tools and applications to connect to multiple OLAP sources. XMLA established a common language for these interactions.

XMLA supports several key operations, including:

• Discover: Retrieving metadata about the OLAP server, such as databases, cubes, dimensions, and measures.
• Execute: Sending commands to the server, such as executing MDX (Multidimensional Expressions) queries, DMX (Data Mining Extensions) queries, or XMLA script commands for data manipulation or schema changes.
• Batch: Grouping multiple XMLA commands into a single request to improve efficiency and ensure atomicity.

While XMLA itself is a protocol, it's commonly used to transmit queries written in:

• MDX (Multidimensional Expressions): The standard query language for querying multidimensional data in OLAP cubes.
• DMX (Data Mining Extensions): Used for querying data mining models.
• Custom XMLA Scripts: For administrative tasks, schema definition, and manipulation.

XMLA can be transmitted over various transport protocols, most commonly:

• HTTP/HTTPS: This is the most widely used transport method, especially for remote access, as it easily traverses firewalls.
• TCP/IP: Direct communication over TCP/IP is also supported, often used for local connections or within trusted networks.

Many business intelligence and data analysis tools leverage XMLA to connect to SQL Server Analysis Services, including:

• Microsoft Excel (Power Pivot)
• Power BI (DirectQuery and Import modes when connecting to Analysis Services)
• SQL Server Management Studio (SSMS)
• Third-party BI and reporting tools
• Custom applications built using ADOMD.NET or AMO (Analysis Management Objects)

When using HTTP as a transport, XMLA messages are typically encapsulated within a SOAP envelope. This allows XMLA to leverage the existing infrastructure and standards of SOAP for message formatting, serialization, and transport.

You can find comprehensive documentation, schema definitions, and usage examples on the Microsoft Learn website. Key resources include:

• XML Element Properties (Microsoft)
• XML Commands
• XMLA Overview

Using XMLA provides several benefits:

• Standardization: Adheres to an industry standard protocol.
• Interoperability: Enables a wide range of tools and applications to connect.
• Flexibility: Supports various transport protocols (HTTP, TCP).
• Metadata Access: Provides robust mechanisms for discovering server metadata.
• Query Execution: Efficiently executes MDX and DMX queries.
• Administrative Capabilities: Allows for management and deployment of Analysis Services objects.