A multilevel hierarchy is a hierarchy of attributes by which users can browse cube data. A multilevel hierarchy is either a user-defined hierarchy defined by using Dimension Designer or is a parent-child hierarchy based on parent-child relationships defined in the underlying dimension table. You define and configure a user-defined hierarchy in Dimension Designer. By default, a user-defined hierarchy of attributes is simply a drill path for users (called an ad hoc or reporting hierarchy); if the hierarchy is a natural hierarchy, defining attribute relationships between them will increase performance because Analysis Services will use these relationships to define aggregations. For more information, see Defining and Configuring an Attribute Relationship.
Parent-child hierarchies are automatically detected by the Dimension Wizard and the Cube Wizard.