Comment by joe_the_user
3 months ago
I think the obvious answer is that client side mapping would let the browser give different view of the data to the client. The obvious problem is that downloading all the data and then transforming is inherently inefficient (and sure, despite this, download-then-process is a common solution used for many problems - but it's problematic to specify the worst solution before you know the problem).
Perhaps there's an alternative universe where javascript lost and an elegant, declarative XSLT could declaratively present data and incrementally download only what's needed, allowing compact and elegant websites.
But in our universe today, this mapping language wound-up a half-thought-idea that just kicked around for a long time in the specs without ever making sense.
My gut instinct is to agree with every bit of that. I admit that I might be missing something, but I've never wanted to send the data once and then have the client view it in multiple transformed ways (minus simple presentation stuff like sorting a table by column and things like that).
And using it to generate RSS as mentioned elsewhere in the comments? That makes perfect sense to me on the server. I don't know that I've ever even seen client-side generated RSS.
But again, this may all be my own lack of imagination.