24542 2014-02-05 23:19:18 +0000 Can we add a note on intrinsically non-streamable axes? 2014-02-17 08:02:09 +0000 1 1 1 Unclassified XPath / XQuery / XSLT XSLT 3.0 Last Call drafts PC Windows NT CLOSED FIXED P2 normal --- 1 abel.braaksma mike cmsmcq public-qt-comments oldest_to_newest 99851 0 abel.braaksma 2014-02-05 23:19:18 +0000 I think it helps if we add a small Note under 19.8.7.7 Streamability of Axis Steps (http://www.w3.org/TR/xslt-30/#streamability-of-axis-steps) mentioning the axes following, following-sibling, preceding, preceding-sibling as being intrinsically non-streamable (unless the context posture is grounded). In line of that, I find it rather odd that we explicitly allow something like this (rule #3): <xsl:value-of select="/preceding::*" /> or: <xsl:value-of select="parent::attribute()/following-sibling::*" /> it's probably clearer to disallow these expressions altogether (i.e., add a rule between #2 and #3 in this section). 99906 1 mike 2014-02-06 12:44:38 +0000 Rule #3 may be (unduly?) influenced by the fact that in Saxon, I do most optimization work before I do streamability analysis, and optimization turns trivially-void expressions such as "/.." and "@comment()" and "@x/following-sibling::*" into "()", making them intrinsically streamable. I would defend the rule, however. We shouldn't make expressions non-streamable unless they really are, and on that basis, streaming of these "void path expressions" is possible. 100384 2 cmsmcq 2014-02-12 10:40:46 +0000 We discussed this in Prague, and were not inclined to make any change; after discussion, the originator expressed agreement with this decision. We noticed that rule 3 in 19.8.7.7 handles /preceding::* but not parent::attribute() or @comment(). The editor may or may not propose to generalize the rule to cover these cases (since they are likely to be error cases, it may not be worth while). 100731 3 mike 2014-02-17 08:02:09 +0000 As suggested in comment #2, I have generalized rule 3 so that it now recognizes steps that are void because the node kind is inconsistent with the axis, as well as those that are void because the axis is inconsistent with the context item type.