lib(xml)


Note for ECLiPSe users

This code creates and accepts character lists rather than ECLiPSe strings. 
To convert between character lists and (UTF8 or ASCII) strings, use the
ECLiPSe built-in string_list/3. For example, to parse a UTF-8 encoded
XML file, use the following code:

xml_parse_file(File, Document) :-
	open(File, read, Stream),
	read_string(Stream, end_of_file, _, Utf8String),
	close(Stream),
	string_list(Utf8String, Chars, utf8),
	xml_parse(Chars, Document).

Most of the subsequent text is taken literally from

http://www.john.fletcher.dial.pipex.com/xml.pl.shtml.



TERMS AND CONDITIONS

This program is offered free of charge, as unsupported source code. You may
use it, copy it, distribute it, modify it or sell it without restriction. 

We hope that it will be useful to you, but it is provided "as is" without
any warranty express or implied, including but not limited to the warranty
of non-infringement and the implied warranties of merchantability and fitness
for a particular purpose.

Binding Time Limited will not be liable for any damages suffered by you as
a result of using the Program. In no event will Binding Time Limited be
liable for any special, indirect or consequential damages or lost profits
even if Binding Time Limited has been advised of the possibility of their
occurrence. Binding Time Limited will not be liable for any third party
claims against you.


History:
$Log: xml_comments.ecl,v $
Revision 1.1.1.1  2006/09/23 01:45:21  snovello
Cisco initial import

Revision 1.1  2003/03/31 13:58:02  js10
Upgraded to latest version from John Fletcher's web site

Revision 1.2  2002/03/26 22:56:55  js10
Added John Fletcher's public domain XML parser/generator

Revision 1.1  2002/03/26 22:50:07  js10
Added John Fletcher's public domain XML parser/generator

Revision 1.1  2002-01-31 21:04:45+00  john
Updated Copyright statements.

Revision 1.0  2001-10-17 20:46:24+01  john
Initial revision


  Background
  xml.pl is a module for parsing 
XML with Prolog, which provides Prolog applications with a simple
interface to XML documents. We have used it successfully in a number of
applications.
  It supports a subset of XML suitable for XML Data and Worldwide Web
  applications. It is neither as strict nor as comprehensive as the XML 1.0 Specification
mandates.
  It is not as strict, because, while the specification must eliminate
ambiguities, not all errors need to be regarded as faults, and some reasonable
examples of real XML usage would have to be rejected if they were.
  It is not as comprehensive, because, where the XML specification makes
  provision for more or less complete DTDs to be provided as part of a
document, xml.pl supports the local definition of ENTITIES only.
  We have placed the code, and a small Windows
application which embodies it, into the public domain, to encourage the use
of Prolog with XML.
  We hope that they will be useful to you, but they are not supported, and
Binding Time Limited accept NO LIABILITY WHATSOEVER in respect of their
use.
  Specification
  Three predicates are exported by the module: xml_parse/[2,3], xml_subterm/2
and xml_pp/1.
  xml_parse( {+Controls}, +?Chars, ?+Document ) parses 
Chars, a list of character codes, to/from a data structure of the form

xml(<attributes>, <content>)
 , where:
  <attributes> is a list of 
 <name>=<data>
 attributes from the (possibly implicit) XML signature of the
document.
  <content> is a (possibly empty) list comprising occurrences of :
  
   
    pcdata(<data>)
    Text
   
   
     comment(<string>)
    An xml comment;
   
   
    namespace(<URI>,<prefix>,<element>)
    a Namespace
   
   
     element(<tag>, <attributes>, <content>)
    <tag>..</tag> encloses <content> or <tag /> if empty
   
   
     instructions(<name>, <data>)
     A PI  <? <name> <data> ?>
   
   
     cdata(<data>)
    <![CDATA[ <string> ]]>
   
   
     doctype(<tag>, <doctype id>)
     DTD <!DOCTYPE .. >
   
   
     
   
   
    The conversions are not completely symmetrical, in that weaker XML is
accepted than can be generated. Specifically, in-bound (Chars ->
Document) parsing does not require strictly well-formed XML. If 
Chars does not represent well-formed XML, Document is
instantiated to the term 
malformed(<attributes>, <content>)
 .
   
   
     
   
   
    The <content> of a malformed/2 structure can include:
   
   
     
   
   
    unparsed( <string> )
    Text which has not been parsed
   
   
    out_of_context( <tag> )
    <tag> is not closed
   
   
    in addition to the parsed term types.Out-bound (Document -> Chars) parsing does require that
Document defines well-formed XML. If an error is detected a 'domain'
exception is raised.The domain exception will attempt to identify the particular sub-term in
error and the message will show a list of its ancestor elements in the form
<tag>{(id)}* where 
<id>
 is the value of any attribute named id.At this release, the Controls applying to in-bound (Chars ->
Document) parsing are:
   
   
     
   
   
    extended_characters(<bool>)
    Use the extended character entities for XHTML (default true)
   
   
     format(<bool>)
    Strip layouts when no non-layout character data appears between elements. default
true)
   
   
    For out-bound (Document -> Chars) parsing, the only available
option is:
   
   
     
   
   
    format(<bool>)
    Indent the element content, (default true)
   
   
     
   
   
    Types
   
   
    <tag>
    An atom naming an element
   
   
    <data>
    A "string"
   
   
    <name>
    An atom, not naming an element
   
   
    <URI>
    An atom giving the URI of a Namespace
   
   
    <string>
    A "string": list of character codes.
   
   
    <doctype id>
    one of public(<string>, <string>), system(<string>) or local
   
   
    <bool>
    one of 'true' or 'false'
   
  
  xml_subterm( +XMLTerm, ?Subterm ) unifies Subterm with
a sub-term of Term. This can be especially useful when trying to
test or retrieve a deeply-nested subterm from a document. Note that 
XMLTerm is a sub-term of itself.
  xml_pp( +XMLDocument )"pretty prints" XMLDocument on
the current output stream.
  Features of xml.pl
  The xml/2 data structure has some useful properties.
  Reusability
  Using an "abstract" Prolog representation of XML, in which terms represent
document "nodes", makes the parser reuseable for any XML application.
  In effect, xml.pl encapsulates the application-independent tasks of document
parsing and generation, which is essential where documents have components
from more than one Namespace.
  Same Structure
  The Prolog term representing a document has the same structure as the
document itself, which makes the correspondence between the literal
representation of the Prolog term and the XML source readily apparent.
  For example, this simple SVG image:
  <?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/.../svg10.dtd"
    [
    <!ENTITY redblue "fill: red; stroke: blue; stroke-width: 1">
    ]>
<svg xmlns="http://www.w3.org/2000/svg" width="500" height="500">
 <circle cx=" 25 " cy=" 25 " r=" 24 " style="&redblue;"/>
</svg>
  ... translates into this Prolog term:
  xml( [version="1.0", standalone="no"],
    [
    doctype( svg, public( "-//W3C//DTD SVG 1.0//EN", "http://www.w3.org/.../svg10.dtd" ) ),
    namespace( 'http://www.w3.org/2000/svg', "",
        element( svg,
            [width="500", height="500"],
            [
            element( circle,
                [cx="25", cy="25", r="24", style="fill: red; stroke: blue; stroke-width: 1"],
                [] )
            ] )
        )
    ] ).
  Efficient Manipulation
  Each type of node in an XML document is represented by a different Prolog
functor, while data, (PCDATA, CDATA and Attribute Values), are left as
"strings", (lists of character codes).
  The use of distinct functors for mark-up structures enables the efficient
recursive traversal of a document, while leaving the data as strings
facilitates application specific parsing of data content (aka 
Micro-parsing).
  For example, to turn every CDATA node into a PCDATA node with tabs expanded
into spaces:
  
cdata_to_pcdata( cdata(CharsWithTabs), pcdata(CharsWithSpaces) ) :-
    tab_expansion( CharsWithTabs, CharsWithSpaces ).
cdata_to_pcdata( xml(Attributes, Content1), xml(Attributes, Content2) ) :-
    cdata_to_pcdata( Content1, Content2 ).
cdata_to_pcdata( namespace(URI,Prefix,Content1), namespace(URI,Prefix,Content2) ) :-
    cdata_to_pcdata( Content1, Content2 ).
cdata_to_pcdata( element(Name,Attrs,Content1), element(Name,Attrs,Content2) ) :-
    cdata_to_pcdata( Content1, Content2 ).
cdata_to_pcdata( [], [] ).
cdata_to_pcdata( [H1|T1], [H2|T2] ) :-
    cdata_to_pcdata( H1, H2 ),
    cdata_to_pcdata( T1, T2 ).
cdata_to_pcdata( pcdata(Chars), pcdata(Chars) ).
cdata_to_pcdata( comment(Chars), comment(Chars) ).
cdata_to_pcdata( instructions(Name, Chars), instructions(Name, Chars) ).
cdata_to_pcdata( doctype(Tag, DoctypeId), doctype(Tag, DoctypeId) ).

  The above uses no 'cuts', but will not create any choice points with ground
input.
  Elegance
  The resolution of entity references and the decomposition of the document
into distinct nodes means that the calling application is not concerned with
the occasionally messy syntax of XML documents.
  For example, the clean separation of namespace nodes means that Namespaces,
which are useful in combining specifications developed separately, have similar
usefulness in combining applications developed separately.
  The source code is available here. Although
it is unsupported, please feel free to 
e-mail queries and suggestions. We will respond as time allows.


