There is a constraint in SS, but it doesn't work the same way as it does in Oracle - i.e., you can't specify it to CASCADE.
In SS, the table being deleted from is aliased as "deleted" - likewise, for an insert or update the table is aliased "inserted" - so the code would look like this.

CREATE TRIGGER mydelete_trigger 
  ON parent_table
 FOR DELETE 
 AS 
  DELETE FROM child_table WHERE iparentid = deleted.iid