On Fri, Dec 18, 2009 at 07:01:36AM -0800, Scott Stafford wrote:
> We don't have a formal spec of it or anything, but from what I can
> tell we evolved the same syntax as the internal Google effort. No
> frills, just a sequence of N field names separated by dots (.). I'll
> try to write out the rules in English, but I might mess this up since
> I'm just doing it from memory...
>
> The 1st through N-1th field can be:
>
> a required/optional Message field_name
> a repeated Message field_name subscripted by [INDEX|
> SUBFIELD_NAME=value]
>
> and the Nth field could be:
>
> a repeated field_name subscripted by [INDEX|SUBFIELD_NAME=value]
> a required, optional, or repeated field_name
>
> INDEX is any integer, where values >=0 indicate the sequence number of
> the element in the repeated field, or <0 in which case it counts from
> the last item, Python-style, so [-1] is the last element.
>
> SUBFIELD_NAME can be any [required|optional] [string|int*] field in
> the field_name Message.
>
> Does that make sense? Sorry it's not a formal syntax, I never took
> that class. ;) I just wrote the parser directly, using
> boost::tokenizer.
>
> If you do write up the formal syntax, please post it!
As I understand formal syntax for Your 'xpath' in BNF like form
looks like:
query ::= query-part | query "." query-part
query-part ::= field-name | field-name "[" selector "]"
selector ::= number | attr-query
attr-query ::= field-name "=" field-value
field-value ::= number | '"' text '"'
field-name ::= text
Here is form with extended predicates that I'd like to see:
query ::= query-part | query "." query-part
query-part ::= field-name | field-name "[" selector "]"
selector ::= number | attr-query
attr-query ::= attr-match | "!" attr-query | "(" attr-query ") | \
attr-query "or" attr-query | attr-query "and" attr-query
attr-match ::= field-name | field-name "=" field-value
field-value ::= number | '"' text '"'
field-name ::= text
Is it acceptable? I'll try to create python implementation of last form.
Pavel
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