row_group: true|false

{
  "DataBaseTables": {
     "TableName": {
        "interface": {
           "fields": { },
           "views": { 
                "default": { 
                   "fields" : [
                      {"field": "cat","row_group": true}
                  ]
                 }
            }
         }
     }
  }
}

When you want in a view to group in Rows for specific field you can set the property row_group=true in the field definition