MARFF：the extension of ARFF format to enable encoding of multi-relational data. Each relation is stored in a seperate file, and the additional meta-data is encoded in such a way that individual tables can still be read into tools requiring the standard ARFF format .

Example: sales, product,customer.

Key:@attribute id integer %<key>%

Foreign Key: @attribute product integer %<foreign products.id>%

File Link:%@ link products.marff 

Link directives appear after the relation name is specified and before attributes are declared.

For Details: http://www.cs.bris.ac.uk/~farrand/marff/