Designing Security for Multidimensional Models in SQL Server Analysis Services

This document provides guidance on designing and implementing security for multidimensional models in SQL Server Analysis Services (SSAS). Effective security design is crucial to protect sensitive data and ensure that users have access only to the information they are authorized to view.

Understanding SSAS Security Models

SQL Server Analysis Services offers a robust security framework that can be implemented at various levels:

• Server Level: Administrators can control access to the SSAS server instance itself.
• Database Level: Permissions can be granted on individual Analysis Services databases.
• Object Level: Access can be restricted to specific cubes, dimensions, hierarchies, measures, and attributes.
• Cell Level: The most granular level, allowing security to be applied to individual data cells within a cube based on specific conditions.

Key Security Concepts

Roles

Roles are fundamental to SSAS security. They are collections of permissions that can be assigned to users or Windows groups. By assigning users to roles, you can efficiently manage access rights. Key role properties include:

• Member Permissions: Define what members (users or groups) can do. Common permissions include Read, Read Definition, Read Data, and Process.
• Scope: Specifies the database objects to which the role's permissions apply.
• Cell Data Access: Defines restrictions on data access at the cell level, often using MDX expressions.
• Dimension Data Scoping: Restricts access to specific members of a dimension.

Permissions

Permissions dictate the actions that users or roles can perform on SSAS objects. These can be granted directly or inherited through roles. Common permissions include:

• Read: Allows users to view the definition and data of an object.
• ReadDefinition: Allows users to view the definition of an object but not its data.
• ReadData: Allows users to view the data of an object but not its definition.
• Process: Allows users to process (update) the object.
• FullControl: Grants all permissions on an object.

Windows Authentication and SSAS Roles

SSAS typically leverages Windows authentication. When creating roles, you associate them with Windows users or Windows security groups. This simplifies user management by aligning SSAS security with your existing Windows infrastructure.

Implementing Security Strategies

Row-Level Security

Row-level security (often referred to as dimension security in SSAS) restricts users' access to specific rows or members within a dimension. This is commonly used for scenarios where different sales representatives should only see data for their own regions.

To implement dimension security:

1. Create a new role in SSAS.
2. Grant the role appropriate member permissions (e.g., Read).
3. In the "Dimension Data" tab of the role, select the dimension you want to secure.
4. Choose "Read" permissions and configure the dimension member restrictions. This often involves creating a security dimension or using custom MDX queries.

Cell-Level Security

Cell-level security provides the finest-grained control, allowing you to restrict access to specific cells within the cube's data. This is useful for hiding sensitive aggregated values or specific transactional data.

To implement cell-level security:

1. Create or modify an existing role.
2. Navigate to the "Cell Data" tab within the role definition.
3. Define an MDX expression that evaluates to the allowed set of cells. For example, you might restrict access to cells where a specific measure group has a value of zero or where a user belongs to a particular department.

Best Practices for Security Design

• Principle of Least Privilege: Grant users only the minimum permissions necessary to perform their tasks.
• Use Windows Groups: Whenever possible, assign roles to Windows security groups rather than individual users. This makes managing users much easier.
• Regular Auditing: Periodically review role memberships and permissions to ensure they are still appropriate.
• Document Your Security Model: Maintain clear documentation of your security roles, their assigned permissions, and the logic behind cell/dimension scoping.
• Test Thoroughly: After implementing security changes, test them rigorously from the perspective of different user roles to confirm they function as expected.

Further Reading

• Security Roles in Analysis Services Multidimensional Models
• Security in Data Access (SQL Server Analysis Services)