[DAS2] version=

[Steve Chervitz]

Andrew Dalke wrote on Mon, 6 Feb 2006 18:42:24
> 
> If we add a version= field to the Content-Type, or whatever
> mechanism is proposed
> 
> Content-Type: application/x-das2features+xml; version=12345
> 
> What will a client do when it gets a version number it has
> never heard of?  Should it use the newest version it supports?
> The oldest?  Abort?

Rather than have version data be something that the client has to discover
in the response, an then have to react to in some intelligent way, how about
adding an optional dasversion field to all requests, such as:

http://www.wormbase.org/das/genome/volvox/1/type?dasversion=1.1

The server would then either:

1) return the appropriate response document if the server supports the
requested version or a later version that is backward compatible with it,
or
2) return a 505 error 'DAS Version Not Supported', which we already have in
the spec.

This puts the onus on the server rather than the client, but I think it
would be less trouble on the server than the alternative scheme would be for
the client. The client can now be fairly dumb about versioning and assume
everything is kosher unless it gets an error.

We could put some of the onus for DAS version support on the revisers of the
spec: When a new version of the spec is released, we'll know right then what
parts will be backward compatible and what parts will not be. The reviser
could document whether the new version of the spec is backwards compatible
with which previous versions, with the appropriate level of granularity
(e.g., "all requests are backward compatible except for the types request").
This would serve as a guide for maintainers of das2 servers.

Thoughts?

Steve