How to create instance using ruby gdsii

how to add bnf parameters while creating instance in gdsii.

errors i am getting while executing above file…
/home/karmic/lib/ruby/gdsii/bnf.rb:285:in block in write': Required data in BNF are not set: XY (RuntimeError) from /home/karmic/lib/ruby/gdsii/bnf.rb:88:inblock in each’
from /home/karmic/lib/ruby/gdsii/bnf.rb:88:in each' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:277:in write' from /home/karmic/lib/ruby/gdsii/group.rb:63:inwrite’
from /home/karmic/lib/ruby/gdsii/bnf.rb:280:in block (2 levels) in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:280:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:280:in block in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:inblock in each’
from /home/karmic/lib/ruby/gdsii/bnf.rb:88:in each' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:277:in write' from /home/karmic/lib/ruby/gdsii/group.rb:63:inwrite’
from /home/karmic/lib/ruby/gdsii/bnf.rb:282:in block in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:inblock in each’
from /home/karmic/lib/ruby/gdsii/bnf.rb:88:in each' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:277:in write' from /home/karmic/lib/ruby/gdsii/group.rb:63:inwrite’
from /home/karmic/lib/ruby/gdsii/bnf.rb:280:in block (2 levels) in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:280:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:280:in block in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:inblock in each’
from /home/karmic/lib/ruby/gdsii/bnf.rb:88:in each' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:277:in write' from /home/karmic/lib/ruby/gdsii/group.rb:63:inwrite’
from /home/karmic/lib/ruby/gdsii/bnf.rb:282:in block in write' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:inblock in each’
from /home/karmic/lib/ruby/gdsii/bnf.rb:88:in each' from /home/karmic/lib/ruby/gdsii/bnf.rb:88:ineach’
from /home/karmic/lib/ruby/gdsii/bnf.rb:277:in write' from /home/karmic/lib/ruby/gdsii/group.rb:63:inwrite’
from test81.rb:20:in block (3 levels) in <class:Somesh>' from /home/karmic/lib/ruby/gdsii/structure.rb:205:inread_each’
from test81.rb:12:in block (2 levels) in <class:Somesh>' from /home/karmic/lib/ruby/gdsii/library.rb:424:inblock in
read_header’
from /home/karmic/lib/ruby/gdsii/mixins.rb:303:in read' from /home/karmic/lib/ruby/gdsii/library.rb:423:inread_header’
from test81.rb:11:in block in <class:Somesh>' from test81.rb:10:inopen’
from test81.rb:10:in <class:Somesh>' from test81.rb:8:in