[This message was posted by David Rosenborg of Pantor Engineering AB <[EMAIL PROTECTED]> to the "FAST Protocol" discussion forum at http://fixprotocol.org/discuss/46. You can reply to it on-line at http://fixprotocol.org/discuss/read/970dd78d - PLEASE DO NOT REPLY BY MAIL.]
Nullability is defined in section 10.4 of the FAST Specification 1.1: "10.4 Nullability Each field has a type that has a nullability property. If a type is nullable, there is a special representation of a NULL value. When a type is non-nullable, no representation for NULL is reserved. All nullable types are constructed in such a way that NULL is represented as a 7-bit entity value where all bits are zero. It is represented as 0x80 when stop bit encoded. Unless explicitly specified, non-nullable representations are used." A mandatory field always has a value logically and it wouldn't make sense to use the notion of NULL in that case. (I say logically because a value is not always physically present in the stream if for example a copy operator is in use.) /David > I am often confronted with the opinion: "Mandatory fields are never > nullable by definition". > > I would like to know, where is this defined? > > The FAST Specification defines only a positive list of all cases in > which nullable types have to be used. There are no information about > forbidden cases. The FAST Protocol - Transfer Encoding Specification - > gives some information about the sense of Null values. It also does not > forbid any combinations of nullable data types and mandatory presence. > > Are there information that explicitly forbid such combinations? > > Reason of question & example: I become aware of a template defintion, > where a field with a nullable supporting integer type is used > differently: > a) optional - no operator > b) mandatory - no operator > > c) is explicitly defined within the FAST specification. It is clear, > that the type have to support Null Values. > > d) is not explicitly defined within the spec. I think, because of the > presence "mandatory", the transfered values of this field would never > be a null value. So, is the property of null support really a problem > in this case??? > > What do you think? [You can unsubscribe from this discussion group by sending a message to mailto:[EMAIL PROTECTED] --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Financial Information eXchange" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/FIX-Protocol?hl=en -~----------~----~----~----~------~----~------~--~---
