What type of data structure is XML?

XML (eXtensible Markup Language) is considered a structured text format because it is designed to store and transport data in a format that is both human-readable and machine-readable. The defining characteristic of XML is its use of tags to delineate the elements of the data. These tags provide semantic context that helps define the data structure, making it easy to understand the organization of the information contained within.

Additionally, XML allows for the hierarchical structuring of data, which is informative for representing complex data relationships. This capacity to structure data clearly within a text format distinguishes XML from other types of data structures like relational databases or spreadsheets, which rely on tables and rows or cells, respectively.

The other options do not accurately categorize XML: relational databases organize data in tables with defined relationships, spreadsheets focus on grid layouts for calculations and data storage, and NoSQL databases include a variety of non-tabular data storage methods, many of which can include different formats. Therefore, labeling XML specifically as a structured text format accurately conveys its core function and design within the realm of data management.