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FAST Protocol
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Re: Template IDs for nested groups
Rolf Andersson / Pantor Engineering
14 Apr 2006 2:26AM ETDavid Rosenborg pointed out to me (the obvious) that even though
you would want to use different templates in a repeating group
it isn't necessarily the case that you'll end up with different
types on the application level (e.g. different representations
for the same application level message). The repeating group
(i.e. the container) would not store heterogeneous items, just
different representations of the same application type.
Thx,
Rolf
> There was little discussion on this and the issue wasn't resolved.
>
> The current TE spec section 2.3.2 says: "Each group has:
> - A presence map if at least one entry in the Group has a default value;
> - A TemplateID field if the group layout cannot be statically deduced;
> meaning that the TemplateID is not fixed but can vary from message
> to message.
> - A size field if the template specifies so. ..."
>
> My intent when I wrote this was to allow what is called "variant
> records" in some programming languages.
>
> (The repeating group would be like a container that supports
> heterogeneous types)
>
> Let's say you want to send a list of messages with different types
> (and layouts) and consequently different TemplateIDs. A repeating
> group that allows a TemplateID for each entry would then be able to
> encode these messages.
>
> Anyway, this construct needs some further discussion.
>
> Thx, Rolf
>
> > Early on I recall some discussions about each group having its own
> > template ID. Was this every formalized or discussed as part of what
> > the consensus feels is in FAST 1.0?
> >
> > Reason for these questions - just trying to tighten up the existing
> > specification a bit.
Re: Template IDs for nested groups
Rolf Andersson / Pantor Engineering 14 Apr 2006 2:26AM ET
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