Data is stored in rows and columns with an index table which contains the locations of the data. A level contains nodes. Each node is linked to nodes beneath it on the next level. As a result each level gets increasingly complex. An example is the file structure on a typical computer.
Hierachical files can be inefficient in some respects.
It is difficult to allow for redundent data. Searching in a hierachial file can also be inefficient since searching may require looking down mutiple levels repeatedly. Relational databases are an extension of the flat file. It consists of a series of related tables. The tables are interconnected via a key field.