- From: Babich, Alan <ABabich@filenet.com>
- Date: Fri, 17 Apr 1998 13:12:12 -0700
- To: "'Saveen Reddy (Exchange)'" <saveenr@Exchange.Microsoft.com>
- Cc: www-webdav-dasl@w3.org
Sauveen: The "00" spec. has <!ELEMENT and (expr+) > <!ELEMENT or (expr+) > to define the syntax for "and" and "or" expressions. However, "and" and "or" are binary operators (which we would like to extend to be n-ary operators, since they are associative and commutative). My understanding of "+" in XML is that it means "one or more". So, the way I read the above syntax is that it allows an "and" expression to have one operand. For example, <d:and> <d:term> <d:lt> <d:value> <d:prop>X</d:prop> </d:value> <d:value> <d:literal>1</d:literal> </d:value> </d:lt> </d:term </d:and> or, translating into the usual mathematical notation, "AND X > 1". However, "and" is not a unary operator, i.e., it takes at least two operands. So, shouldn't the syntax be <!ELEMENT and (expr, expr+) > <!ELEMENT or (expr, expr+) > to force at least two operands for "and" and "or"? Now, I realize that we could extend "and" and "or" to unary operators by defining them to be the identity operator if they have just one operand. However, I would oppose that, as it would not be doing a favor to any implementer translating the XML query expression into SQL or whatever he needs to translate it to. The implementer would have to make a special case out of that, but nothing is gained for the effort. I would rather have unary "and" and "or" operators be illegal syntax by using the revised syntax shown above. I'm new to XML, so I may have missed the point, so, what are your comments? Alan Babich
Received on Friday, 17 April 1998 16:14:12 UTC