Subject: Re: [xsl] Does the count() function require access to the whole subtree? From: Wolfgang Laun <wolfgang.laun@xxxxxxxxx> Date: Thu, 16 Jan 2014 17:23:16 +0100 |
OK, I understand that some expressions can be collected while the input document streams through the system. But what is the possible consequence of *emitting* the result into the output document, e.g., if I need to omit it "up front"? Does this mean that the output is held back or its construction delayed? Or can the way a result is used make streaming impossible? -W On 16/01/2014, Wendell Piez <wapiez@xxxxxxxxxxxxxxx> wrote: > Hi, > > Just a question prompted by David's commentary: > > On Thu, Jan 16, 2014 at 6:44 AM, David Carlisle <davidc@xxxxxxxxx> wrote: >> Some operations are intrinsically not streamable, if you replace data() >> by reverse() for example then reverse(//x) is going to have to buffer >> every node somewhere and return the x elements in reverse order so since >> it has to return the last one first the operation can't be streamed in >> any reasonable way irrespective of the input sequence, which happens to >> be //x here. So nesting of x would not be relevant. > > I imagine that even in this case, streaming might not be completely > useless when used within a pipeline. > > For example, your pipeline could collect all //x (streaming) and then > reverse them (not streaming). > > In principle, you would need only the memory for holding //x (or > rather, copies of //x or pointers to them), not the entire collection > within which they are found. > > This is correct, isn't it? I imagine the general principle here is > that pipelining and streaming play well together. > > I also had a related question, back in September. It wasn't answered > (rare for this list), either because it wasn't clear, or because XML > Summer School was going on at the time. Or both. > > http://xsl-list.markmail.org/thread/pwuzpcvdoi7eam4h > > Cheers, Wendell > > Wendell Piez | http://www.wendellpiez.com > XML | XSLT | electronic publishing > Eat Your Vegetables > _____oo_________o_o___ooooo____ooooooo_^
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