Public review comments for WSBD-v1.0-csprd015 Live Preview

[Vernon Craddock <vcraddock@cloverleafsolutions.com>]

Comment type [editorial | technical] ? technical

Impact [major | minor] ? minor

The meaning and use of the relationship element is unclear.  Section 5.1 
defines that it must start with "livePreview", but no reasoning is 
provided.  Presumably, if there are multiple values, the client 
application should/could  provide these as options in a select box?

Live preview that is easy to implement and support is going to be 
critical to widespread acceptance of this standard.
This specification seems to indicate that "multipart/x-mixed-replace" is 
the way to accomplish this.  This is easy to implement on browsers that 
support it, but you have to rely on browser detection scripts to 
determine if it is not supported. Section 6.15.2.2 recommends using a 
live stream to provide textual feedback, but offers no suggestions on 
how to implement this, or describe the implementation to the client.
Server Sent events may provide a richer preview mechanism for some 
sensor types.  This is also not supported by all browsers, but detection 
of support in javascript is much simpler - 'if (typeof(EventSource) !== 
"undefined")'  The event stream can also be returned from a restful web 
service call.  We used this in our working prototype implementation of 
wsbd sending events containing text sensorStatus, fingerQuality, and 
even base64 encoded preview images.  We would like to see 
Content-Type:text/event-stream included in appendix B as an allowed mime 
type.

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