Need some way preventing duplicate edges on the same pair of vertex.

### ArcadeDB Version: <version here, you can find it on the first line of server output>
### JDK Version: OpenJDK 11
### OS: Win7 64bit

Ex: When run this command "CREATE EDGE Own FROM aPerson TO aPet" multiple times, I don't want the DB create multiple 'Own' edges to the same pet. How can I do? I read the document but nowhere mentions about this.
