Glad you are enjoying the series, and thanks for your question.
You are correct, all of your data is structured, regardless of where it comes from or the format it is in - a file contains columns and rows, for example.
It's all about how the data is stored in Azure, and how Microsoft apply terms to your data. Anything stored in a database table, for instance, is defined as structured. Anything in an unmanaged file which we've dumped into the data lake is deemed to be unstructured.
So, the line is drawn as:
- If your data is in a file, Microsoft's terminology defines your data as unstructured (because to Azure, it's just a file)
- If your data is in a table, Azure knows about the structure of the data (columns, data types etc), so Microsoft define that as structured
Hope this is clear, come back to me if you have further questions.