[Xpath-ng] Thoughts on work products

[Uche Ogbuji]

> Hi Uche,
> 
> I'm glad that you've set up this mailing list, and that you've posted
> this overview of how you see things progressing. I think that sorting
> out our goals is very important.
> 
> > Mike Kay just raised concerns on XML-DEV about our using the term
> > "XPath NG", claiming it might cause confusion in the community. I
> > disagree. I think it's no more confusing than, say the names "EXSLT"
> > or "JDOM", but we certainly should have an umbrella name for the
> > specifications we work on (distinct from the name of this mailing
> > list). I plump for "XPath NG", but we could also come up with
> > something cute such as "NextPath". I'm sure "XPath++" would also
> > fall afould of Mike's objections.
> 
> "FIXPath" (no particular expansion, or maybe Functional, Intuitive
> XPath ;)

I like this.  Preferrably expansion-less :-)

> "PaX" (Paths for XML)

Don't like this so well.

> > As to what we produce, I think we should take a leaf out of the
> > EXSLT playbook. I think we should produce relatively self-contained
> > modules, each of which exhibits healthy coupling and cohesion.
> 
> I think that modularity is absolutely key to XPath NG. But I think
> that to support that modularity we need a good core on which we can
> build -- we need to specify what makes up the core data model and
> syntax and how this data model and syntax can be built on within the
> modules.

Good point.

> For example, I started writing a kind of spec a while ago that said,
> of values:
> 
>   Every value in XPath NG is a sequence containing zero or more items.

As David R mentioned, I'd rather just call these "lists".

>   The items in a sequence can be of three kinds: nodes, values and
>   other sequences. Nodes are items that have identity whereas values
>   are items that do not have identity.
> 
>   There are three core types of values in XPath NG: strings, numbers
>   and booleans. These values can be cast to each other using the XPath
>   1.0 rules. The only difference is that in XPath NG, strings that
>   hold numbers in scientific notation can be cast to numbers, 'INF' is
>   converted to Infinity and '-INF' is converted to negative Infinity.
> 
>   Sequences are cast to strings and numbers by converting the first
>   item of the sequence to a string or number; if the sequence is empty
>   you get an empty string or NaN. Sequences are cast to boolean true
>   if they contain any items, boolean false if they do not.
> 
>   Other modules may add more data types, but every data type must
>   define a mapping onto a string, a number and a boolean value, and
>   how that data type is created from a sequence.

This passage sounds very good.  My only questions are whether we allow lists 
of lists, and whether lists are homogeneous or hetero.


> This is basically the same as XPath 1.0 except that it allows
> sequences of normal values and that it specifically indicates what
> kinds of additional data types are allowed and what a module must do
> to specify them.

I do think we should come up with a system for such specifications, along the 
lines of our XML-DEV thread from a couple of months ago.


> (I'm not proposing that this is how we define values, just trying to
> illustrate the principal of defining a core that we can then build
> on.)
> 
> 
> I think we probably all have modules that we're particular interested
> in pursuing. I'm interested in looking at supporting schema
> information and in supporting access to LMNL structures, for example.
> It looks like David Rosenborg is interested in the functional
> programming support and in making XPath a stand-alone language. I
> think that having these divergent goals should really help us make the
> core something that is flexible and extensible -- we can check as we
> go along that the facilities we build into the core are sufficient to
> support the modules that we want to build on top of it.
> 
> So my first priorities would be to focus on the core data model and
> expression syntax on which the modules can be built.

Cool.  Let's do it...


-- 
Uche Ogbuji                                    Fourthought, Inc.
http://uche.ogbuji.net    http://4Suite.org    http://fourthought.com
Python&XML column: 2. Introducing PyXML - http://www.xml.com/pub/a/2002/09/25/p
y.html
The Past, Present and Future of Web Services 1 - http://www.webservices.org/ind
ex.php/article/articleview/663/1/24/
The Past, Present and Future of Web Services 2 - 'http://www.webservices.org/in
dex.php/article/articleview/679/1/24/
Serenity through markup - http://adtmag.com/article.asp?id=6807
Tip: Using generators for XML processing - http://www-106.ibm.com/developerwork
s/xml/library/x-tipgenr.html