NoSQL databases are the digital equivalent of a basement level archive with pallets full of boxes more or less organized. They typically can't function as a primary database of record or even an operational data store. It's the transactional or meta-data layer that "rules" all the other disparate data stores. For example, on the Hadoop platform, HCatalog, the meta-data layer that maps files to logical tables names, must be a relational database like MySQL or SQL Server.