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Internet Technologies Xml Namespaces Internet Technologies

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/ Internet Technologies

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. Internet Technologies

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. Internet Technologies

Namespaces • Prefixes are bound to namespace URI’s by attaching • an xmlns:prefix attribute to the the prefixed element • or 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. The • name RDF is therefore an element from this namespace. Internet Technologies

Namespaces • Bindings have scope within the element in which they’re • declared 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> Internet Technologies

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. Internet Technologies

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 is in no namespace. Internet Technologies

Declaring Namespaces xmlns:pre=“someURN” is fine xmlns:pre=“” is illegal xmlns=“someURN” is fine xmlns=“” legal and same as no namespace Internet Technologies

Some Examples From The W3C Specification <x xmlns:edi='http://ecommerce.org/schema'>  <edi:price units='Euro'>32.18</edi:price></x> Internet Technologies

<x xmlns:edi='http://ecommerce.org/schema'>  <lineItem edi:taxClass="exempt">Baby food</lineItem></x> Internet Technologies

<?xml version="1.0"?><html:html xmlns:html='http://www.w3.org/TR/REC-html40'> <html:head><html:title>Frobnostication</html:title><?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> Internet Technologies

<?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> Internet Technologies

<?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> Internet Technologies

<?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></book> Internet Technologies

<?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> <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> Internet Technologies

<?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><?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 scope of the declaration, of there being no default namespace. Internet Technologies

<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> Internet Technologies

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

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; Internet Technologies

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/"; Internet Technologies

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"); Internet Technologies

// 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(""); } } Internet Technologies

Output 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> Internet Technologies

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