Generated file catalog.ttl has invalid syntax

[pedropaulofb]

The catalog.ttl file generated by the ontouml2owl-batch function is reporting a syntax problem at line 11.

The problem is: ERROR: Expected IRI to follow prefix "foaf:" on line 11.
Line 11 is: @prefix foaf: <<http://xmlns.com/foaf/0.1/>.

Note that a double < char is used.

Can you please correct that? The solution is remove the double char, leaving only one.

[pedropaulofb]

In addition, as you're already going to edit the function, could you please add the following prefix to the generated ttl files (catalog.ttl and also the ontology.ttl files):

@prefix dataset: <http://purl.org/ontouml-models/dataset/>.

This is going to reduce the ttl files' size in about 25%, which is a big gain at it currently have almost 30 MB.

This request was also made here: OntoUML/ontouml-models#181

[pedropaulofb]

This issue can be closed after the PR #105 is accepted.