Re: Implementation issues of OPTIONAL

Hi Lee,

Thank you very much for your answer.

'If you find that a particular implementation does not behave 
in a way you expect, you might consider contacting the implementer to 
determine why.'

My worry is that if the implementations are not strictly following the 
SPARQL specifications, 
then it might: firstly, misguide the SPARQL user in understanding the real 
semantics of SPARQL; 
secondly, make linking open data from different sources more difficult.
Nevertheless, I understand this is not the responsibility of the SPARQL 
working group to make sure 
the implementations are strictly following the Specification. 

'We would be grateful if you would acknowledge that your comment has been 
answered by sending a reply to this mailing list.'

Your answer 
'there is no "NULL" and an unmatched variable is not simply 
not bound to any value and is available to be bound in a later clause.'
clearly answered my question, and I am very pleased to confirm my comments 
has been answered. 
Thank you very much!

best regards,
Hong