Q:

Does the 'Relational' Foundation of Database Theory enable 'Ashley Madison'-like attacks?

Again and again hackers use SQL injection to get information from the backend database. Is it fair to say because a relational database by its nature has all the links within the data sets (e.g., 1-to-1, 1-to-* and so on), therefore it enables a user with any form of access to illegally access everything, either in theory or practice?

A:

How data is related or not within the database has nothing to do with SQLi. Flat files, NoSQL, etc. will not affect the ability for a user to perform unauthorized access to data.
SQLi is about unsecured direct access to the database (in whatever form that is), resulting in a user manipulating that access in order to obtain data without the expected authorization. 

