Hierarchies most commonly include attributes connected to their parents by to-one associations. However, it may be necessary to also include attributes that can take multiple values for each single value of their parent attributes.
| A multiple arc between two dimensional attributes states that those attributes have a many-to-many relationship. |
A multiple arc may also enter a dimension: for instance, in the healthcare industry, you may want to model the fact that each hospital admission is associated to multiple diagnoses.
