Re: [xml-dev] Accurate line and column numbers for elements and attribut

[John Snelson <john.snelson@ORACLE.COM>]

Hi Leigh,

There's a reason that most XML parsers don't report accurate line and 
column numbers - the XML specification makes it difficult in a number of 
ways. For instance, the namespaces spec basically requires that all 
attributes of an element be parsed before the element can be reported, 
which often means that line and column information for the attributes is 
lost. Similarly, the XML spec applies attribute value normalization to 
each attribute value, meaning that the original position of characters 
in the source document is lost.

What a lot of XML tools end up doing is reporting a line number and then 
doing something like quoting the attribute value marked with the 
position of the error. This is quite unsatisfactory when you're used to 
accurate line and column numbers from other tools - especially for 
programming languages.

In writing my own parser FAXPP [1] (in C, so not great for you), one of 
my aims was to be able to use it to report accurate line and column 
numbers when parsing XSLT. In order to do that it has an option to turn 
off attribute value normalization - but of course the application then 
has to perform the same operation later to be described as a conformant 
XML parser.

John

[1] http://faxpp.sourceforge.net/

Klotz, Leigh wrote:
> I'm developing an XML representation for a templating system which can
> report errors at both parse and at execution time.
> 
> The existing system does a good job of reporting input file line numbers
> on its element- and attribute-like constructs, and I'd like to provide
> that same functionality with the XML representation.
> 
> Most SAX2 implementations (including the default one with recent Sun
> Java systems) offer start and end line numbers of tags, but provide only
> the ending column number of element content.
> 
> While I'm able to make use of this information, the most critical need
> for column numbers comes in attribute values, so that errors in
> attribute-value template expressions can be reported with column numbers
> accurate in the original input stream.  SAX2 is no help here, as the
> attributes spring forth fully formed as if from Zeus's forehead.
> 
> I've taken a look at Piccolo, which has a commented-out set of column
> number info (on elements only), and at Micahel Kay's suggestion of using
> the Saxon AugmentedSource (
> http://www.nabble.com/-xml-dev--Line-number-of-a-node-to7990605.html#a79
> 90605 ) but again this provides only line numbers, not column numbers,
> and not for attributes.
> 
> Does anyone have experience or recommendations for a non-validating,
> namespace-aware XML parser in Java which supports or can easily be made
> to support accurate beginning line and column numbers of both elements
> and attributes (and maybe text)?  The solution needs to be released
> under a BSD license.
> 
> Thank you,
> Leigh.

-- 
John Snelson, Oracle Corporation            http://snelson.org.uk/john
Berkeley DB XML:            http://oracle.com/database/berkeley-db/xml
XQilla:                                  http://xqilla.sourceforge.net