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Second patch from Paul Dubois, Daniel

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Daniel Veillard 2000-03-02 00:15:55 +00:00
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2 changed files with 120 additions and 112 deletions
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@ -1,3 +1,7 @@
Thu Mar 2 03:03:50 CET 2000 Daniel Veillard <Daniel.Veillard@w3.org>
* doc/xml.html : applied second patch from Paul DuBois
Tue Feb 29 23:55:13 CET 2000 Daniel Veillard <Daniel.Veillard@w3.org>
* doc/xml.html : applied patch from Paul DuBois

228
doc/xml.html
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@ -53,7 +53,7 @@ XML is a standard for building tag-based structured documents/data.</p>
<li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX
like interface</a>; the interface is designed to be compatible with <a
href="http://www.jclark.com/xml/expat.html">Expat</a>.</li>
<li>Libxml now include a nearly complete <a
<li>Libxml now includes a nearly complete <a
href="http://www.w3.org/TR/xpath">XPath</a> implementation.</li>
<li>Libxml exports Push and Pull type parser interfaces for both XML and
HTML.</li>
@ -110,15 +110,15 @@ href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> list.</p>
<h2><a name="Downloads">Downloads</a></h2>
<p>Latest versions can be found on <a
<p>The latest versions of libxml can be found on <a
href="ftp://rpmfind.net/pub/libxml/">rpmfind.net</a> or on the <a
href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either
as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source
archive</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/contrib/rpms/">RPMs
packages</a> (NOTE that you need both the <a
packages</a>. (NOTE that you need both the <a
href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a
href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a>
packages installed to compile applications using libxml).</p>
packages installed to compile applications using libxml.)</p>
<p><a name="Snapshot">Snapshot:</a></p>
<ul>
@ -209,7 +209,7 @@ for really accurate description</h3>
<h3>1.8.3: Jan 5 2000</h3>
<ul>
<li>a Push interface for the XML and HTML parsers</li>
<li>an shell like interface to the document tree (try tester --shell
<li>a shell-like interface to the document tree (try tester --shell
:-)</li>
<li>lots of bug fixes and improvement added over XMas hollidays</li>
<li>fixed the DTD parsing code to work with the xhtml DTD</li>
@ -338,18 +338,18 @@ returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an
the file name, the document type, and a <strong>root</strong> pointer which
is the root of the document (or more exactly the first child under the root
which is the document). The tree is made of <strong>xmlNode</strong>s, chained
in double linked lists of siblings and with childs&lt;->parent relationship.
in double-linked lists of siblings and with childs&lt;->parent relationship.
An xmlNode can also carry properties (a chain of xmlAttr structures). An
attribute may have a value which is a list of TEXT or ENTITY_REF nodes.</p>
<p>Here is an example (erroneous w.r.t. the XML spec since there should be
only one ELEMENT under the root):</p>
<p>Here is an example (erroneous with respect to the XML spec since there
should be only one ELEMENT under the root):</p>
<p><img src="structure.gif" alt=" structure.gif "></p>
<p>In the source package there is a small program (not installed by default)
called <strong>tester</strong> which parses XML files given as argument and
prints them back as parsed. This is useful to detect errors both in XML code
prints them back as parsed. This is useful for detecting errors both in XML code
and in the XML parser itself. It has an option <strong>--debug</strong> which
prints the actual in-memory structure of the document, here is the result with
the <a href="#example">example</a> given before:</p>
@ -383,27 +383,28 @@ standalone=true
TEXT
content=...</pre>
<p>This should be useful to learn the internal representation model.</p>
<p>This should be useful for learning the internal representation model.</p>
<h2><a name="interface">The SAX interface</a></h2>
<p>Sometimes the DOM tree output is just too large to fit reasonably into
memory. In that case and if you don't expect to save back the XML document
loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
memory. In that case (and if you don't expect to save back the XML document
loaded using libxml), it's better to use the SAX interface of libxml. SAX is a
<strong>callback-based interface</strong> to the parser. Before parsing, the
application layer registers a customized set of callbacks which are called
by the library as it progresses through the XML input.</p>
<p>To get a more detailed step-by-step guidance on using the SAX interface of
libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> has written <a
href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice
documentation.</a></p>
<p>To get more detailed step-by-step guidance on using the SAX interface of
libxml, see the
href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">nice
documentation.</a> written by <a href="mailto:james@daa.com.au">James
Henstridge</a>.</p>
<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
program located in the gnome-xml module (it's usually not shipped in the
binary packages of libxml, but you can also find it in the tar source
binary packages of libxml, but you can find it in the tar source
distribution). Here is the sequence of callbacks that would be reported by
testSAX when parsing the example given before:</p>
testSAX when parsing the example XML document shown earlier:</p>
<pre>SAX.setDocumentLocator()
SAX.startDocument()
SAX.getEntity(amp)
@ -448,40 +449,40 @@ specific interface.</p>
<h2><a name="library">The XML library interfaces</a></h2>
<p>This section is directly intended to help programmers getting bootstrapped
using the XML library from the C language. It doesn't intent to be extensive,
I hope the automatically generated docs will provide the completeness
required, but as a separated set of documents. The interfaces of the XML
library are by principle low level, there is nearly zero abstration. Those
using the XML library from the C language. It is not intended to be extensive.
I hope the automatically generated documents will provide the completeness
required, but as a separate set of documents. The interfaces of the XML
library are by principle low level, there is nearly zero abstraction. Those
interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
<p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are
separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>,
let's have a look at how it can be called:</p>
separated from the <a href="gnome-xml-htmlparser.html">HTML parser
interfaces</a>. Let's have a look at how the XML parser can be called:</p>
<h3><a name="Invoking">Invoking the parser : the pull way</a></h3>
<h3><a name="Invoking">Invoking the parser : the pull method</a></h3>
<p>Usually, the first thing to do is to read an XML input, the parser accepts
to parse both memory mapped documents or direct files. The functions are
<p>Usually, the first thing to do is to read an XML input. The parser accepts
documents either from in-memory strings or from files. The functions are
defined in "parser.h":</p>
<dl>
<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
<dd><p>parse a zero terminated string containing the document</p>
<dd><p>Parse a null-terminated string containing the document.</p>
</dd>
</dl>
<dl>
<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
<dd><p>parse an XML document contained in a file (possibly compressed)</p>
<dd><p>Parse an XML document contained in a (possibly compressed) file.</p>
</dd>
</dl>
<p>This returns a pointer to the document structure (or NULL in case of
<p>The parser returns a pointer to the document structure (or NULL in case of
failure).</p>
<h3 id="Invoking1">Invoking the parser: the push way</h3>
<h3 id="Invoking1">Invoking the parser: the push method</h3>
<p>In order for the application to keep the control when the document is been
fetched (common for GUI based programs) the libxml, as of version 1.8.3
provides a push interface too, here are the interfaces:</p>
fetched (which is common for GUI based programs) libxml provides a push
interface, too, as of version 1.8.3. Here are the interface functions:</p>
<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
void *user_data,
const char *chunk,
@ -492,7 +493,7 @@ int xmlParseChunk (xmlParserCtxtPtr ctxt,
int size,
int terminate);</pre>
<p>and here is a simple use example:</p>
<p>and here is a simple example showing how to use the interface:</p>
<pre> FILE *f;
f = fopen(filename, "r");
@ -514,8 +515,8 @@ int xmlParseChunk (xmlParserCtxtPtr ctxt,
}
}</pre>
<p>Also note that the HTML parser embedded into libxml also have a push
interface they are just prefixed by "html" instead of "xml"</p>
<p>Also note that the HTML parser embedded into libxml also has a push
interface; the functions are just prefixed by "html" rather than "xml"</p>
<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
@ -524,16 +525,16 @@ memory-hungry, first to load the document in memory, second to build the tree.
Reading a document without building the tree is possible using the SAX
interfaces (see SAX.h and <a
href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
Henstridge documentation</a>), not also that the push interface can be limited
to SAX, just use the two first arguments of
Henstridge's documentation</a>). Note also that the push interface can be
limited to SAX. Just use the two first arguments of
<code>xmlCreatePushParserCtxt()</code>.</p>
<h3><a name="Building">Building a tree from scratch</a></h3>
<p>The other way to get an XML tree in memory is by building it. Basically
there is a set of functions dedicated to building new elements, those are also
described in "tree.h", here is for example the piece of code producing the
example used before:</p>
there is a set of functions dedicated to building new elements. (These are also
described in "tree.h".) For example, here is a piece of code that produces the
XML document used in the previous examples:</p>
<pre> xmlDocPtr doc;
xmlNodePtr tree, subtree;
@ -554,64 +555,66 @@ example used before:</p>
<h3><a name="Traversing">Traversing the tree</a></h3>
<p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code
has access to the internal structure of all the element of the tree. The names
has access to the internal structure of all the elements of the tree. The names
should be somewhat simple like <strong>parent</strong>,
<strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>,
<strong>properties</strong>, etc... For example still with the previous
<strong>properties</strong>, etc... For example, still with the previous
example:</p>
<pre><code>doc->root->childs->childs</code></pre>
<p>points to the title element,</p>
<pre>doc->root->childs->next->child->child</pre>
<p>points to the text node containing the chapter titlle "The Linux adventure"
and</p>
<p>points to the text node containing the chapter title "The Linux adventure".
</p>
<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
present before the document root, so doc->root may point to an element which
is not the document Root Element, a function
present before the document root, so <code>doc->root</code> may point to an
element which is not the document Root Element, a function
<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
<h3><a name="Modifying">Modifying the tree</a></h3>
<p>functions are provided to read and write the document content, here is an
excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
<p>Functions are provided for reading and writing the document content. Here
is an excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
<dl>
<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
xmlChar *value);</code></dt>
<dd><p>This set (or change) an attribute carried by an ELEMENT node the
value can be NULL</p>
<dd><p>This sets (or changes) an attribute carried by an ELEMENT node. The
value can be NULL.</p>
</dd>
</dl>
<dl>
<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
*name);</code></dt>
<dd><p>This function returns a pointer to the property content, note that
no extra copy is made</p>
<dd><p>This function returns a pointer to the property content. Note that
no extra copy is made.</p>
</dd>
</dl>
<p>Two functions must be used to read an write the text associated to
<p>Two functions are provided for reading and writing the text associated with
elements:</p>
<dl>
<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
*value);</code></dt>
<dd><p>This function takes an "external" string and convert it to one text
node or possibly to a list of entity and text nodes. All non-predefined
entity references like &amp;Gnome; will be stored internally as an
entity node, hence the result of the function may not be a single
entity references like &amp;Gnome; will be stored internally as
entity nodes, hence the result of the function may not be a single
node.</p>
</dd>
</dl>
<dl>
<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
inLine);</code></dt>
<dd><p>this is the dual function, which generate a new string containing
<dd><p>This function is the inverse of <code>xmlStringGetNodeList()</code>.
It generates a new string containing
the content of the text and entity nodes. Note the extra argument
inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
the string it will substitute it with it's value say "GNU Network Object
Model Environment". Set it if you want to use the string for non XML
usage like User Interface.</p>
inLine. If this argument is set to 1, the function will expand entity
references. For example, instead of returning the &amp;Gnome; XML
encoding in the string, it will substitute it with its value (say,
"GNU Network Object Model Environment"). Set this argument if you want
to use the string for non-XML usage like User Interface.</p>
</dd>
</dl>
@ -621,53 +624,53 @@ elements:</p>
<dl>
<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
*size);</code></dt>
<dd><p>returns a buffer where the document has been saved</p>
<dd><p>Returns a buffer into which the document has been saved.</p>
</dd>
</dl>
<dl>
<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
<dd><p>dumps a buffer to an open file descriptor</p>
<dd><p>Dumps a document to an open file descriptor.</p>
</dd>
</dl>
<dl>
<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
<dd><p>save the document ot a file. In that case the compression interface
is triggered if turned on</p>
<dd><p>Saves the document to a file. In this case, the compression interface
is triggered if it has been turned on.</p>
</dd>
</dl>
<h3><a name="Compressio">Compression</a></h3>
<p>The library handle transparently compression when doing file based
accesses, the level of compression on saves can be tuned either globally or
<p>The library transparently handles compression when doing file-based
accesses. The level of compression on saves can be turned on either globally or
individually for one file:</p>
<dl>
<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
<dd><p>Get the document compression ratio (0-9)</p>
<dd><p>Gets the document compression ratio (0-9).</p>
</dd>
</dl>
<dl>
<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
<dd><p>Set the document compression ratio</p>
<dd><p>Sets the document compression ratio.</p>
</dd>
</dl>
<dl>
<dt><code>int xmlGetCompressMode(void);</code></dt>
<dd><p>Get the default compression ratio</p>
<dd><p>Gets the default compression ratio.</p>
</dd>
</dl>
<dl>
<dt><code>void xmlSetCompressMode(int mode);</code></dt>
<dd><p>set the default compression ratio</p>
<dd><p>Sets the default compression ratio.</p>
</dd>
</dl>
<h2><a name="Entities">Entities or no entities</a></h2>
<p>Entities principle is similar to simple C macros. They define an
abbreviation for a given string that you can reuse many time through the
content of your document. They are especially useful when frequent occurrences
of a given string may occur within a document or to confine the change needed
<p>Entities in principle are similar to simple C macros. An entity defines an
abbreviation for a given string that you can reuse many times throughout the
content of your document. Entities are especially useful when a given string
may occur frequently within a document, or to confine the change needed
to a document to a restricted area in the internal subset of the document (at
the beginning). Example:</p>
<pre>1 &lt;?xml version="1.0"?>
@ -680,23 +683,24 @@ the beginning). Example:</p>
<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
it's name with '&amp;' and following it by ';' without any spaces added. There
are 5 predefined entities in libxml allowing to escape charaters with
are 5 predefined entities in libxml allowing you to escape charaters with
predefined meaning in some parts of the xml document content:
<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
the letter '>', <strong>&amp;apos;</strong> for the letter ''',
<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
for the letter '&amp;'.</p>
<strong>&amp;lt;</strong> for the character '&lt;', <strong>&amp;gt;</strong>
for the character '>', <strong>&amp;apos;</strong> for the character ''',
<strong>&amp;quot;</strong> for the character '"', and
<strong>&amp;amp;</strong> for the character '&amp;'.</p>
<p>One of the problems related to entities is that you may want the parser to
substitute entities content to see the replacement text in your application,
or you may prefer keeping entities references as such in the content to be
able to save the document back without loosing this usually precious
information (if the user went through the pain of explicitley defining
substitute an entity's content so that you can see the replacement text in your
application.
Or you may prefer to keep entity references as such in the content to be
able to save the document back without losing this usually precious
information (if the user went through the pain of explicitly defining
entities, he may have a a rather negative attitude if you blindly susbtitute
them as saving time). The function <a
them as saving time). The <a
href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
allows to check and change the behaviour, which is to not substitute entities
by default.</p>
function allows you to check and change the behaviour, which is to not
substitute entities by default.</p>
<p>Here is the DOM tree built by libxml for the previous document in the
default case:</p>
@ -720,46 +724,46 @@ version=1.0
TEXT
content= Extensible Markup Language</pre>
<p>So entities or no entities ? Basically it depends on your use case, I
suggest to keep the non-substituting default behaviour and avoid using
<p>So, entities or no entities? Basically, it depends on your use case. I
suggest that you keep the non-substituting default behaviour and avoid using
entities in your XML document or data if you are not willing to handle the
entity references elements in the DOM tree.</p>
<p>Note that at save time libxml enforce the conversion of the predefined
entities where necessary to prevent well-formedness problems, and will also
transparently replace those with chars (i.e. will not generate entity
reference elements in the DOM tree nor call the reference() SAX callback when
transparently replace those with chars (i.e., it will not generate entity
reference elements in the DOM tree or call the reference() SAX callback when
finding them in the input).</p>
<h2><a name="Namespaces">Namespaces</a></h2>
<p>The libxml library implement namespace @@ support by recognizing namespace
<p>The libxml library implements namespace @@ support by recognizing namespace
contructs in the input, and does namespace lookup automatically when building
the DOM tree. A namespace declaration is associated with an in-memory
structure and all elements or attributes within that namespace point to it.
Hence testing the namespace is a simple and fast equality operation at the
user level.</p>
<p>I suggest it that people using libxml use a namespace, and declare it on
the root element of their document as the default namespace. Then they dont
need to happend the prefix in the content but we will have a basis for future
<p>I suggest that people using libxml use a namespace, and declare it in
the root element of their document as the default namespace. Then they don't
need to use the prefix in the content but we will have a basis for future
semantic refinement and merging of data from different sources. This doesn't
augment significantly the size of the XML output, but significantly increase
it's value in the long-term.</p>
its value in the long-term.</p>
<p>Concerning the namespace value, this has to be an URL, but this doesn't
have to point to any existing resource on the Web. I suggest using an URL
within a domain you control, which makes sense and if possible holding some
kind of versionning informations. For example
<p>Concerning the namespace value, this has to be an URL, but the URL doesn't
have to point to any existing resource on the Web. I suggest that it makes
sense to use an URL within a domain you control, and that the URL
should contain some kind of version information if possible. For example,
<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
Then when you load a file, make sure that a namespace carrying the
version-independant prefix is installed on the root element of your document,
version-independent prefix is installed on the root element of your document,
and if the version information don't match something you know, warn the user
and be liberal in what you accept as the input. Also do *not* try to base
namespace checking on the prefix value &lt;foo:text> may be exactly the same
as &lt;bar:text> in another document, what really matter is the URI
associated with the element or the attribute, not the prefix string which is
just a shortcut for the full URI.</p>
namespace checking on the prefix value. &lt;foo:text> may be exactly the same
as &lt;bar:text> in another document. What really matter is the URI
associated with the element or the attribute, not the prefix string (which is
just a shortcut for the full URI).</p>
<p>@@Interfaces@@</p>
@ -767,11 +771,11 @@ just a shortcut for the full URI.</p>
<p>Usually people object using namespace in the case of validation, I object
this and will make sure that using namespaces won't break validity checking,
so even is you plan or are using validation I strongly suggest to add
namespaces to your document. A default namespace scheme
so even is you plan to use or currently are using validation I strongly suggest
adding namespaces to your document. A default namespace scheme
<code>xmlns="http://...."</code> should not break validity even on less
flexible parsers. Now using namespace to mix and differenciate content coming
from mutliple Dtd will certainly break current validation schemes, I will try
flexible parsers. Now using namespace to mix and differentiate content coming
from multiple DTDs will certainly break current validation schemes. I will try
to provide ways to do this, but this may not be portable or standardized.</p>
<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
@ -911,9 +915,9 @@ only a couple of functions, browsing the tree to gather the informations and
generate the internals structures is harder, and more error prone.</p>
<p>The suggested principle is to be tolerant with respect to the input
structure. For example the ordering of the attributes is not significant, Cthe
structure. For example, the ordering of the attributes is not significant, Cthe
XML specification is clear about it. It's also usually a good idea to not be
dependant of the orders of the childs of a given node, unless it really makes
dependent of the orders of the childs of a given node, unless it really makes
things harder. Here is some code to parse the informations for a person:</p>
<pre>/*
* A person record
@ -1043,6 +1047,6 @@ base under gnome-xml/example</p>
<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
<p>$Id: xml.html,v 1.25 2000/02/29 22:57:47 veillard Exp $</p>
<p>$Id: xml.html,v 1.26 2000/03/01 00:40:41 veillard Exp $</p>
</body>
</html>