46-929 web technologies1 web technologies week four advanced dom and working with namespaces

46-929 Web Technologies 1

Web Technologies

Week Four

Advanced DOM and Working with namespaces


Notes on XML Namespaces

Namespace notes taken and adapted from “XML in a Nutshell”By Harold and Means

Java examples adapted from “XML and Java” – course text

Namespace specification is at:

http://www.w3.org/TR/REC-xml-names/


Namespaces

Primary purpose:

To disambiguate element and attribute names.

Implementation:

• Attach a prefix to an element or attribute name.• Map the prefix to a URI. This need not be a real place.• Default URI’s may also be provided for those

elements with no prefix.• The URI’s partition the elements and attributes into

disjoint sets.


Namespaces

• Each prefix is associated with one URI.• Names with prefixes associated with the same URI are in the same namespace.• Elements and attributes in namespaces have names with

exactly one colon. • The text before the colon is called the prefix.• The text after the colon is called the local part.• The complete name, including the colon, is called the qualified name.


Namespaces

• Prefixes are bound to namespace URI’s by attaching an xmlns:prefix attribute to the the prefixed elementor one of its ancestors

For example:

<rdf:RDF xmlns:rdf=http://www.w3.org/TR/REC-rdf-syntax#>

associates the prefix rdf with the namespace URI shown. Thename RDF is therefore an element from this namespace.

http://www.w3.org/TR/REC-rdf-syntax


Namespaces

• Bindings have scope within the element in which they’redeclared and its contents.

<rdf:RDF xmlns:rdf=http://www.w3.org/TR/REC-rdf-syntax#>

<!– within this element the prefix rdf is associated with the RDF namespace

</rdf:RDF>





Namespaces

The default namespace

• Is set using the xmlns attribute (with no prefix)• Applies only to elements not attributes

<SomeTag xmlns=“someURI”> <insideTag> … </insideTag> </SomeTag>

SomeTag and insideTag are both in the someURI namespace.


Namespaces

If there is no default namespace is declared then tags without Prefixes are in no namespace at all. Not even the default one.

The only way an attribute belongs to a namespace is if it has a declared prefix.

<rdf:RDF xmlns:rdf=“http://www.w3.org/TR/REC-rdf-syntax#> <rdf:Description about=“someValue”> : </rdf:Description>

</rdf:RDF>

The about attribute isin no namespace.





Declaring Namespaces

xmlns:pre=“someURN” is finexmlns:pre=“” is illegal

xmlns=“someURN” is finexmlns=“” legal and same as no namespace

Some Examples From The W3C Specification

<x xmlns:edi='http://ecommerce.org/schema'>  <edi:price units='Euro'>32.18</edi:price></x>

<?xml version="1.0"?><html:html xmlns:html='http://www.w3.org/TR/REC-html40'> <html:head><html:title>Frobnostication</html:title> </html:head> <html:body><html:p>Moved to <html:a href='http://frob.com'>here.</html:a></html:p> </html:body></html:html>

<?xml version="1.0"?><bk:book xmlns:bk='urn:loc.gov:books' xmlns:isbn='urn:ISBN:0-395-36341-6'> <bk:title>Cheaper by the Dozen</bk:title> <isbn:number>1568491379</isbn:number></bk:book>

<?xml version="1.0"?><html xmlns='http://www.w3.org/TR/REC-html40'> <head><title>Frobnostication</title></head> <body><p>Moved to <a href='http://frob.com'>here</a>.</p></body></html>

<?xml version="1.0"?><book xmlns='urn:loc.gov:books' xmlns:isbn='urn:ISBN:0-395-36341-6'> <title>Cheaper by the Dozen</title> <isbn:number>1568491379</isbn:number></book>

<?xml version="1.0"?><book xmlns='urn:loc.gov:books' xmlns:isbn='urn:ISBN:0-395-36341-6'> <title>Cheaper by the Dozen</title> <isbn:number>1568491379</isbn:number> <notes>  <p xmlns='urn:w3-org-ns:HTML'> This is a <i>funny</i> book! </p> </notes></book>

<?xml version='1.0'?><Beers>  <table xmlns='http://www.w3.org/TR/REC-html40'> <th><td>Name</td><td>Origin</td><td>Description</td></th> <tr>  <td><brandName xmlns="">Huntsman</brandName></td> <td><origin xmlns="">Bath, UK</origin></td> <td> <details xmlns=""><class>Bitter</class><hop>Fuggles</hop> <pro>Wonderful hop, light alcohol, good summer beer</pro> <con>Fragile; excessive variance pub to pub</con> </details> </td> </tr> </table> </Beers>

The default namespace can be set to the empty string. This has the same effect, within the scopeof the declaration, of there being no default namespace.

<x xmlns:n1="http://www.w3.org" xmlns:n2="http://www.w3.org" > <bad a="1" a="2" /> <bad n1:a="1" n2:a="2" /></x>

<x xmlns:n1="http://www.w3.org" xmlns="http://www.w3.org" > <good a="1" b="2" /> <good a="1" n1:a="2" /></x>


Namespaces and Java

// Exploring the NamespaceCorrector class in Chapter 4 of// XML and Java

// Example 1

import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.apache.xml.serialize.OutputFormat;import org.apache.xml.serialize.XMLSerializer;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Text;


public class NamespaceExplore {

static final String NS = "http://www.andrew.cmu.edu/~mm6"; // the assigned namespace to the xml:lang attribute static final String XML_NS = "http://www.w3.org/XML/1998/namespace";

// the assigned namespace of the xmlns attribute static final String XMLNS_NS = "http://www.w3.org/2000/xmlns/";


public static void main(String[] argv) throws Exception {

DocumentBuilderFactory dbfactory = DocumentBuilderFactory.newInstance(); dbfactory.setNamespaceAware(true); DocumentBuilder builder = dbfactory.newDocumentBuilder(); Document factory = builder.newDocument(); OutputFormat format = new OutputFormat("xml", "UTF-8", true); XMLSerializer serializer = new XMLSerializer(System.out, format);

// build a top element within a namespace Element top = factory.createElementNS(NS, "mm6:GradeBook");


// define an xmlns attribute within this top element top.setAttributeNS(XMLNS_NS, "xmlns:mm6", NS);

// define an xml:lang attribute within this top element top.setAttributeNS(XML_NS, "xml:lang", "en");

Element student = factory.createElementNS(NS,"mm6:Student"); top.appendChild(student);

Text t = factory.createTextNode("87.5"); student.appendChild(t);

serializer.serialize(top); System.out.println(""); }}


D:\McCarthy\www\95-733\examples\chap04>java NamespaceExplore

<?xml version="1.0" encoding="UTF-8"?><mm6:GradeBook xml:lang="en" xmlns:mm6= "http://www.andrew.cmu.edu/~mm6"> <mm6:Student>87.5</mm6:Student></mm6:GradeBook>

Output


Attributes and Namespaces// Exploring the NamespaceCorrector class in Chapter 4 of// XML and Java

// Example 2 Looking at Attributes

import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.apache.xml.serialize.OutputFormat;import org.apache.xml.serialize.XMLSerializer;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Text;import org.w3c.dom.NamedNodeMap;import org.w3c.dom.Attr;


public class NamespaceExplore2 {

static final String NS = "http://www.andrew.cmu.edu/~mm6"; // the assigned namespace to the xml:lang attribute static final String XML_NS = "http://www.w3.org/XML/1998/namespace";

// the assigned namespace of the xmlns attribute static final String XMLNS_NS = "http://www.w3.org/2000/xmlns/";

Same as before


public static void main(String[] argv) throws Exception {

DocumentBuilderFactory dbfactory = DocumentBuilderFactory.newInstance(); dbfactory.setNamespaceAware(true); DocumentBuilder builder = dbfactory.newDocumentBuilder(); Document factory = builder.newDocument(); OutputFormat format = new OutputFormat("xml", "UTF-8", true); XMLSerializer serializer = new XMLSerializer(System.out, format);

Same as before


// build a top element within a namespace Element top = factory.createElementNS(NS, "mm6:GradeBook");

// define an xmlns attribute within this top element top.setAttributeNS(XMLNS_NS, "xmlns:mm6", NS);

// define an xml:lang attribute withing this top element top.setAttributeNS(XML_NS, "xml:lang", "en");

// create a Student tag Element student = factory.createElementNS(NS,"mm6:Student"); // add a prefixed attribute to Student student.setAttributeNS(NS,"mm6:StudentID", "123-34-8765");

top.appendChild(student);We are creating attributes withnamespaces.


Text t = factory.createTextNode("87.5"); student.appendChild(t);

serializer.serialize(top); System.out.println("");

// display the attributes in the student tag showNamespaceOfAttributes(student);

// display the attributes in the top tag

showNamespaceOfAttributes(top); }


public static void showNamespaceOfAttributes(Element e) {

System.out.println("Display attributes of " + e.getTagName()); NamedNodeMap map = e.getAttributes(); for (int i = 0; i < map.getLength(); i++) { Attr attr = (Attr)map.item(i); String prefix = attr.getPrefix(); String name = attr.getName(); String val = attr.getValue(); String uri = attr.getNamespaceURI(); System.out.println("Attribute ====>" + name); System.out.println(" prefix =" + prefix); System.out.println(" value = " + val); System.out.println(" NS URI = " + uri); }

}}


OutputD:\McCarthy\www\95-733\examples\chap04>java NamespaceExplore2<?xml version="1.0" encoding="UTF-8"?><mm6:GradeBook xml:lang="en“ xmlns:mm6="http://www.andrew.cmu.edu/~mm6"> <mm6:Student mm6:StudentID="123-34-8765">87.5 </mm6:Student></mm6:GradeBook>

Display attributes of mm6:StudentAttribute ====>mm6:StudentID prefix =mm6 value = 123-34-8765 NS URI = http://www.andrew.cmu.edu/~mm6


Display attributes of mm6:GradeBookAttribute ====>xml:lang prefix =xml value = en NS URI = http://www.w3.org/XML/1998/namespaceAttribute ====>xmlns:mm6 prefix =xmlns value = http://www.andrew.cmu.edu/~mm6 NS URI = http://www.w3.org/2000/xmlns/


NCTest.java – XML and Java

// NCTest.java Listing 4.2 XML and Java

import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.apache.xml.serialize.OutputFormat;import org.apache.xml.serialize.XMLSerializer;import org.w3c.dom.Document;import org.w3c.dom.Element;


public class NCTest { static final String NS0 = "http://example.com/@"; static final String NS1 = "http://example.com/a"; static final String XML_NS = "http://www.w3.org/XML/1998/namespace";

static final String XMLNS_NS = "http://www.w3.org/2000/xmlns/";

public static void main(String[] argv) throws Exception { DocumentBuilderFactory dbfactory = DocumentBuilderFactory.newInstance(); dbfactory.setNamespaceAware(true); DocumentBuilder builder = dbfactory.newDocumentBuilder(); Document factory = builder.newDocument(); OutputFormat format = new OutputFormat("xml", "UTF-8", true); XMLSerializer serializer = new XMLSerializer(System.out, format);


Element top = factory.createElementNS(null, "Address"); top.setAttributeNS(XMLNS_NS, "xmlns:p", NS0);

// Add an element that has the namespace and no prefix. Element el1 = factory.createElementNS(NS1, "Zip"); // el1 has an attribute of which namespace is // the same as el1. el1.setAttributeNS(NS1, "p:id", ""); el1.appendChild(factory.createElementNS(null, "Zip2")); top.appendChild(el1);

// Add an element that has the namespace and prefix. Element el2 = factory.createElementNS(NS1, "p:State"); // add an attribute to el2 -- code deleted -- no harm mistake in book el2.setAttributeNS(XML_NS, "xml:lang", "en"); top.appendChild(el2);


Element el3 = factory.createElementNS(NS0, "p:City"); top.appendChild(el3);

// Prints the tree before correction. serializer.serialize(top); System.out.println("");

// Correct NamespaceCorrector.correct(top); // Prints the tree after correction. serializer.reset(); serializer.serialize(top); System.out.println("");

What does the output document look like?

Now, what does theoutput document look like?


// Another test: // p:Country and p:iso2 have the same prefix but // different namespaces. Element el4 = factory.createElementNS(NS0, "p:Country"); el4.setAttributeNS(NS1, "p:iso2", "ja"); // This should throw an exception. NamespaceCorrector.correct(el4); }}

What does this documentlook like and whycan’t it be repaired?


D:\McCarthy\www\95-733\examples\chap04>javac NCTest.java

D:\McCarthy\www\95-733\examples\chap04>java NCTest

<?xml version="1.0" encoding="UTF-8"?><Address xmlns:p="http://example.com/@"> <Zip p:id=""> <Zip2/> </Zip> <p:State xml:lang="en"/> <p:City/></Address>

This is not as the authorintended.


<?xml version="1.0" encoding="UTF-8"?><Address xmlns:p="http://example.com/@"> <Zip p:id="" xmlns="http://example.com/a" xmlns:p="http://example.com/a"> <Zip2 xmlns=""/> </Zip> <p:State xml:lang="en" xmlns:p="http://example.com/a"/> <p:City/></Address>

Corrected document.


Exception in thread "main" org.w3c.dom.DOMException: Namespace inconsistence at NamespaceCorrector.set(NamespaceCorrector.java:89) at NamespaceCorrector.correctElement(NamespaceCorrector.java:78) at NamespaceCorrector.correct(NamespaceCorrector.java:26) at NCTest.main(NCTest.java:67)

Too bad to fix.


NamespaceCorrector.java // NamespaceCorrector.java

import org.w3c.dom.Attr;import org.w3c.dom.DOMException;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NamedNodeMap;


/** * Add required namespace declarations. */public class NamespaceCorrector { private static final String XMLNS_NS = "http://www.w3.org/2000/xmlns/";

private NamespaceCorrector() { }


/** @param node The top node of target nodes */

public static void correct(Node node) { switch (node.getNodeType()) { case Node.ELEMENT_NODE: correctElement((Element)node); // Fall down case Node.DOCUMENT_NODE: case Node.DOCUMENT_FRAGMENT_NODE: case Node.ENTITY_REFERENCE_NODE: for (Node ch = node.getFirstChild(); ch != null; ch = ch.getNextSibling()) { correct(ch); } break; } }


/** * Check whether the prefixes and the namespaces of el and * its attributes are declared or not. * if not, add a namespace declaration to el. */ private static void correctElement(Element el) { // Check el. String prefix = el.getPrefix(); String current = el.getNamespaceURI(); String declared = howDeclared(el, prefix);


if (prefix == null) { if (current == null && declared == null) { // ok } else if (current == null || declared == null) { set(el, prefix, current == null ? "" : current); } else if (!current.equals(declared)) { set(el, prefix, current); }} else { if (current == null) throw new DOMException( DOMException.NAMESPACE_ERR, el.getNodeName() +" has no namespace"); if (declared == null || !current.equals(declared)) set(el, prefix, current); }


// Check attributes of el. NamedNodeMap map = el.getAttributes(); for (int i = 0; i < map.getLength(); i++) { Attr attr = (Attr)map.item(i); prefix = attr.getPrefix(); if (prefix == null || prefix.equals("xml") || prefix.equals("xmlns")) continue; current = attr.getNamespaceURI(); declared = howDeclared(el, prefix); if (declared == null || !current.equals(declared)) { set(el, prefix, current); i = -1; // map has changed. // So restart the loop. } } }


private static void set(Element el, String prefix, String ns) { String qname = prefix == null ? "xmlns" : "xmlns:"+prefix;

if (el.getAttributeNode(qname) != null) throw new DOMException(DOMException.NAMESPACE_ERR, "Namespace inconsistence"); el.setAttributeNS(XMLNS_NS, qname, ns); }


/** * Search <var>context</var> and ancestors for declaration * of prefix. * @param prefix Prefix, or <code>null</code> for default ns. */ private static String howDeclared(Element context, String prefix) { String qname = prefix == null ? "xmlns" : "xmlns:"+prefix;


for (Node node = context; node != null; node = node.getParentNode()) { if (node.getNodeType() == Node.ELEMENT_NODE) { Attr attr = ((Element)node).getAttributeNode(qname); if (attr != null) { if (prefix == null && attr.getNodeValue().equals("")) return null; else return attr.getNodeValue(); } } } return null; }}


Homework

Trace the NamespaceCorrector.java program for the following cases: Case 1:

An element has a namespace but no prefix. An ancestorof the element has a default namespace with the same namespace value.

Case 2: An element has a namespace but no prefix and no

default namespace exists.


Case 3.An element has a namespace but no prefix and anancestor has a different default namespace.

Case 4.An element has a namespace but no prefix andthis element declares a different default namespace.

Case 5.An element has a namespace and a prefixthat points to a different namespace.

46-929 web technologies1 web technologies week four advanced dom and working with namespaces

Documents