RE: Should the XPath working group add support for an importcapability?

[David Lee <dlee@calldei.com>]

IMHO ...
XPath is not intended as a fully featured language but rather a common expression vocabulary.
The fully featured languages that use XPath themselves support modularity and other features useful to a fully fledged language.  If you want those features just use the right language.  Say XQuery or XSLT depending on what you want.
Any XPath expression is a valid XQuery program.

----------------------------------------
David A. Lee
dlee@calldei.com
http://www.xmlsh.org

-----Original Message-----
From: Costello, Roger L. [mailto:costello@mitre.org] 
Sent: Monday, January 14, 2013 9:12 AM
To: xml-dev@lists.xml.org
Subject: [xml-dev] Should the XPath working group add support for an import capability?

Hi Folks,

The new functionality in XPath 3.0 is very exciting.

With its new functionality one can create powerful XPath data structures, functions (unfortunately not libraries, see below) and programs -- all written in pure XPath. 

Since XPath is highly portable the programs can be dropped into any language that hosts XPath - XSLT, XQuery, Java, Perl, Python, etc.. That is fantastic. Write once and reuse many times.

    Imagine a function library developer
    able to write just one set of functions, 
    not two. The developer would save a 
    massive amount of time and could use
    these savings in writing more functions 
    in the library -- a bonus to everyone.

There is one problem, however.

The XPath programs must be monolithic (not modular). One cannot write program A and then reuse it (import it) into program B.

    The current W3C XPath 3.0 specification 
    does not include support for an "import" 
    clause.

That non-modularity of XPath limits its usefulness.

I would like to see the XPath working group add modularity to the XPath language.

Here are the advantages to doing so:

1. Develop once, reuse often. That results in time and cost savings.

2. Computer Scientist John Hughes, in his famous paper "Why Functional Programming Matters" argues that "modularity is the key to successful programming." Greater modularity in XPath would yield more successful programs.

Here are the disadvantages to doing so:

1. It makes the language bigger. Vendors are less inclined to support XPath if it is too big.

2. It is not in the XPath working group's requirements.  A new use-case / requirement would have to be inserted into the XPath requirements / use-cases.

What do you think, should the XPath working group add support for modularity (i.e., add support for an import capability)?

If yes, now is the time to speak up. Also, if yes, should the XPath working group add it to 3.0 or 3.1?

/Roger

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