Which of the following is NOT a classification of data?

The classification of data typically includes structured, unstructured, and semi-structured categories. Structured data is highly organized and easily searchable, often residing in databases, where it follows a predefined model. Unstructured data lacks a clear structure, such as text, images, or video content, making it more challenging to analyze. Semi-structured data is a hybrid that does not fit neatly into a traditional database but still has some organizational properties, like metadata, which helps in data management.

The term "hierarchical," while it describes a type of data organization in certain contexts, does not represent a distinct classification of data as the other three do. Instead, hierarchical structures can be applied to various types of data, such as in file systems or organizational charts. Hence, it does not fit the framework of data classification categories like the others listed.