Which one of the following would usually be classified as structured data?

Structured data refers to information that is organized in a predefined manner, often in rows and columns, making it easily searchable and manageable by software applications. It typically resides in databases or spreadsheets where each piece of data has a specific format.

In this scenario, a set of customer address details fits the definition of structured data perfectly. The addresses can be formatted in a consistent manner, comprising individual fields such as names, street addresses, cities, states, and zip codes. This organized structure allows for easy retrieval and analysis using database querying languages like SQL.

In contrast, the other options represent forms of unstructured or semi-structured data. For instance, an inter-office email may contain varied content, formatting, and attachments, making it more difficult to categorize systematically. An online video demonstration is a multimedia format lacking inherent structure, as it does not present information in a standardized format. Similarly, the contents of a letter to a supplier can vary greatly in format and structure, making them harder to analyze systematically.

Thus, the set of customer address details stands out as the clear example of structured data, as it is organized in a way that can be easily processed and analyzed.