What is the difference between a flat-file and multi-relational database, and when would it be appropriate to use each?

A flat file database is a database that is designed around a single table and puts all database information in one table with fields to represent all parameters and may contain many fields often with duplicate data, whereas a multi relational database incorporates multiple tables with methods for the tables to work together. Flat file databases are appropriate to use when there's need to share with external sources as the offer the functionality to store information, manipulate fields,print formatted information and exchange it with others through the Internet. Multi relational databases are appropriate to use when creating databases that are dependent on relationships of the fields.