The following Figure shows how hierarchies of metrics are represented.<br/>MetricDefinitions can be related to one another in a variety of ways.  One way is in a hierarchy of definitions, such as a calculation hierarchy.  <br/>MetricDefinitionHierarchy provides the ability to define any number of hierarchical relationships.  MetricDefinitionHierarchyMember represents the relationship between two MetricDefinitions in a hierarchy, one playing the parent role and the other playing the role of a child.  <br/>For example, video sessions, with a synthetic scalar metric such as an estimated MOS (Mean Opinion Score), a number between 1 and 5; the per-session MOS KPI is computed using different low-level counters (packet loss, delay, delay variation, NE port-level frame counters, and so forth.  <br/>Another type of relationship could indicate one MetricDefinition has been replaced by another or could be used instead of another.<br/>