Which of the following statements about Hierarchies is true?

A hierarchy is a way to organize data into levels that represent relationships and meaningful ordering within a dataset. The first statement asserts that a hierarchy shows relationships among groups of columns, which is accurate. In a hierarchy, each level represents a facet of the data that can be related to other levels, allowing for nuanced data analysis.

For example, consider a geographic hierarchy where you have levels like Country, State, and City. This demonstrates clear relationships among the groups of columns corresponding to these hierarchical levels, allowing users to drill down or aggregate data as necessary.

The correctness of this statement is rooted in how hierarchies function in data models—they provide a structured way to navigate through data dimensions that enhance understanding and reporting.

The other statements present limitations or misconceptions. For instance, stating that all hierarchies must have unique lowest levels or that a dimension table can have just one hierarchy are not universally true across scenarios. Also, requiring multiple parent columns in each hierarchy is not a necessity; a hierarchy can be structured around a single parent-child relationship. Therefore, the first statement accurately captures the essence and utility of hierarchies in data organization.