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Internet Technologies 1 Internet Technologies Xml Namespaces
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Internet Technologies
Xml Namespaces
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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”
Namespace specification is at:
http://www.w3.org/TR/REC-xml-names/
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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.
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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.
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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.
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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>
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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.
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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.
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Declaring Namespaces
xmlns:pre=“someURN” is finexmlns:pre=“” is illegal
xmlns=“someURN” is finexmlns=“” legal and same as no namespace
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Some Examples From The W3C Specification
<x xmlns:edi='http://ecommerce.org/schema'> <!-- the 'price' element's namespace is http://ecommerce.org/schema --> <edi:price units='Euro'>32.18</edi:price></x>
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<x xmlns:edi='http://ecommerce.org/schema'> <!-- the 'taxClass' attribute's namespace is http://ecommerce.org/schema --> <lineItem edi:taxClass="exempt">Baby food</lineItem></x>
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<?xml version="1.0"?><!-- all elements here are explicitly in the HTML namespace --><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>
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<?xml version="1.0"?><!-- both namespace prefixes are available throughout --><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>
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<?xml version="1.0"?><!-- elements are in the HTML namespace, in this case by default --><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>
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<?xml version="1.0"?><!-- unprefixed element types are from "books" --><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>
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<?xml version="1.0"?><!-- initially, the default namespace is "books" --><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> <!-- make HTML the default namespace for some commentary --> <p xmlns='urn:w3-org-ns:HTML'> This is a <i>funny</i> book! </p> </notes></book>
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<?xml version='1.0'?><Beers> <!-- the default namespace is now that of HTML --> <table xmlns='http://www.w3.org/TR/REC-html40'> <th><td>Name</td><td>Origin</td><td>Description</td></th> <tr> <!-- no default namespace inside table cells --> <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.
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<!-- http://www.w3.org is bound to n1 and n2 --><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>
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<!-- http://www.w3.org is bound to n1 and is the default --><x xmlns:n1="http://www.w3.org" xmlns="http://www.w3.org" > <good a="1" b="2" /> <good a="1" n1:a="2" /></x>
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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;
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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/";
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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");
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// 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(""); }}
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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
