When learning Distributed Storage System,I faced a basic question: what are structured unstructured and semistructured data and their differeces.I already know simple differences between them, What I want to know are how to differ them inside.
Structured Data is SQL like structures where the number of fields (columns) is fixed and every entry in the collection (table) has the same structure. References to other collections/tables are 'hardwired' via foreign keys.
Unstructured Data is like MongoDB where a collection is a loose association of documents which do not require to have the same structure. Each document can have different elements and references to other documents can be ad hoc.
Semi-structured systems are various hybrids of the two. For example Google's Firebase repository each document must have the same elements; however, relationships are ad hoc. Semi-structured data often include semantics like inheritance and isA vs. hasA relationships.