[XSL-LIST Mailing List Archive Home] [By Thread] [By Date]

Re: [xsl] Does the count() function require access to the whole subtree?

---

---

Exactly, this is what I tried to express in my first reply: that
count() is not "whitewashing" its argument, and so you can't
say  "count() is streamable, period".

-W

On 13/01/2014, Michael Kay <mike@xxxxxxxxxxxx> wrote:
>
>>
>> My first question in other words: Is count( x ) always streamable, no
>> matter what x (or a $x or...) is?
>
> No. Counter-example: count(following-sibling::x) is not streamable.
>
> More specifically, count(X) is streamable (more specifically, its posture is
> grounded) if the posture of X is grounded, climbing, striding, or crawling,
> but not if it is roaming.
>
> Sorry - I know that's a lot of new jargon to absorb on a Monday morning!
>
> Michael Kay
> Saxonica
>
>
>>
>> The "positioned" was referring to a quote from Roger, see his post,
>> please.
>>
>> -W
>>
>>
>> On 13/01/2014, Michael Kay <mike@xxxxxxxxxxxx> wrote:
>>>
>>> On 13 Jan 2014, at 11:59, Wolfgang Laun <wolfgang.laun@xxxxxxxxx> wrote:
>>>
>>>> With growing insecurity ;-)
>>>>
>>>> My understanding is that count($x) may be called on the construction
>>>> of a sequence which (the construction) is not streamable, and that
>>>> calling count(...) on it does not make it streamable.
>>>>
>>>> Another thing: calling count(...) doesn't require to be positioned
>>>> anywhere.
>>>>
>>>
>>> Sorry, but I'm afraid I don't even understand what you're saying/asking
>>> here. What do you mean by an expression being positioned?
>>>
>>> What we are discussing, is in simplified terms, the fact that count(//x)
>>> is
>>> streamable, but data(//x) is not. Here //x is a "crawling" expression -
>>> one
>>> that selects nodes which may overlap each other. When an expression
>>> returns
>>> (potentially) overlapping nodes, the W3C spec says you can apply
>>> inspection
>>> operations like count() to those nodes, but you cannot apply absorption
>>> expressions like data(), because doing so would require buffering.
>>>
>>> Michael Kay
>>> Saxonica

---