Roles in Multidimensional Modeling

Roles in SQL Server Analysis Services (SSAS) provide a mechanism for controlling access to data within a multidimensional database. By defining roles, administrators can grant specific permissions to users or groups, ensuring that they can only access the data they are authorized to see.

Understanding Role-Based Security

Role-based security is a fundamental aspect of securing your Analysis Services multidimensional models. It allows you to:

• Granular Access Control: Restrict access to specific cubes, dimensions, hierarchies, attributes, or even individual cells within the cube.
• Data Segregation: Ensure that different users or groups see only the data relevant to their responsibilities. For example, a sales manager might see all sales data, while a regional manager only sees data for their region.
• Simplified Management: Manage permissions by assigning users to roles, rather than managing permissions for each individual user.

Creating and Managing Roles

Roles are typically created and managed using SQL Server Management Studio (SSMS) or SQL Server Data Tools (SSDT).

Steps to Create a Role:

1. In SSMS or SSDT, connect to your Analysis Services instance.
2. In Object Explorer, expand your Analysis Services database.
3. Right-click on the Roles folder and select New Role.
4. In the Role Name field, enter a descriptive name for the role (e.g., "Sales Managers", "Product Analysts").
5. On the General page, you can specify membership by adding Windows users or groups.
6. Configure the specific permissions on the subsequent pages:
   • Cell Data: Define restrictions on cell data access. This can be done by creating restrictions on measures or by using MDX expressions.
   • Dimension Data: Control access to specific members within dimensions. This is often achieved using an MDX query to filter dimension members.
   • Cube Permissions: Grant permissions at the cube level, such as read access or administrative control.
   • Database Permissions: Define overall database permissions, like browsing or processing.
7. Click OK to save the role.

Permissions Overview:

Permission	Description
Read	Allows users to browse the database and query data.
ReadAllData	Allows users to read all data, including cell data.
ReadDefinition	Allows users to read the metadata and structure of the database.
Read(Cube Name)	Allows users to read data from a specific cube.
ReadDefinition(Cube Name)	Allows users to read the metadata of a specific cube.
Read(Dimension Name)	Allows users to read data from a specific dimension.
ReadDefinition(Dimension Name)	Allows users to read the metadata of a specific dimension.
Read(Measure Group Name)	Allows users to read data from a specific measure group.

Cell Data Restrictions

Cell data restrictions allow you to limit access to specific values within the cube. This is powerful for scenarios where users should only see their own data or data relevant to their scope.

Restrictions can be applied based on:

• Measures: Restricting access to specific measures.
• MDX Expressions: Writing an MDX query that defines which cells are accessible. For example, a query could restrict access to sales data only for the user's assigned region.

Example MDX for Cell Restriction:

            IIF(
                &[Geography].[Country].CurrentMember.Name = "USA",
                1,
                0
            )
            

This MDX expression would grant access to data only if the current member of the "Country" attribute in the "Geography" dimension is "USA".

Dimension Data Restrictions

Dimension data restrictions enable you to filter the visible members of a dimension. This is commonly used to implement hierarchical security, where users can only see data pertaining to their assigned portion of a dimension hierarchy.

Restrictions are typically defined using an MDX query that returns a set of members that the user is allowed to see.

Example MDX for Dimension Restriction:

            SELECT {[Geography].[Country].Members} ON ROWS FROM [Adventure Works]
            WHERE ([Sales Territory].[Sales Territory Country].&[United States])
            

This MDX query would allow users in this role to see only members from the "United States" within the "Sales Territory Country" hierarchy.

Note: Properly configuring roles is crucial for maintaining data security and integrity in your Analysis Services solutions. Always test role permissions thoroughly to ensure they behave as expected.

Best Practices

• Use Windows Groups: Assign Windows groups to roles rather than individual users for easier management.
• Principle of Least Privilege: Grant only the minimum permissions necessary for a user or group to perform their tasks.
• Regular Auditing: Periodically review role assignments and permissions to ensure they are still appropriate.
• Clear Naming Conventions: Use descriptive names for roles to easily understand their purpose.