1. Orgnizational and Distibuted Object Technologies 1 OCT Xml Namespaces

2. Orgnizational and Distibuted Object Technologies 2 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/

3. Orgnizational and Distibuted Object Technologies 3 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.

4. Orgnizational and Distibuted Object Technologies 4 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.

5. Orgnizational and Distibuted Object Technologies 5 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: 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.

6. Orgnizational and Distibuted Object Technologies 6 Namespaces Bindings have scope within the element in which they’re declared and its contents. http://www.w3.org/TR/REC-rdf-syntax# <!– within this element the prefix rdf is associated with the RDF namespace 

7. Orgnizational and Distibuted Object Technologies 7 Namespaces The default namespace Is set using the xmlns attribute (with no prefix) Applies only to elements not attributes … SomeTag and insideTag are both in the someURI namespace.

8. Orgnizational and Distibuted Object Technologies 8 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. http://www.w3.org/TR/REC-rdf-syntax# : The about attribute is in no namespace.

9. Orgnizational and Distibuted Object Technologies 9 Declaring Namespaces xmlns:pre=“someURN” is fine xmlns:pre=“” is illegal xmlns=“someURN” is fine xmlns=“” legal and same as no namespace

10. Orgnizational and Distibuted Object Technologies 10 Some Examples From The W3C Specification <!-- the 'price' element's namespace is http://ecommerce.org/schema --> 32.18

11. Orgnizational and Distibuted Object Technologies 11 <!-- the 'taxClass' attribute's namespace is http://ecommerce.org/schema --> Baby food

12. Orgnizational and Distibuted Object Technologies 12 Frobnostication Moved to here.

13. Orgnizational and Distibuted Object Technologies 13 Cheaper by the Dozen 1568491379

14. Orgnizational and Distibuted Object Technologies 14 <!-- elements are in the HTML namespace, in this case by default --> Frobnostication Moved to here.

15. Orgnizational and Distibuted Object Technologies 15 Cheaper by the Dozen 1568491379

16. Orgnizational and Distibuted Object Technologies 16 Cheaper by the Dozen 1568491379 <!-- make HTML the default namespace for some commentary --> This is a funny book!

17. Orgnizational and Distibuted Object Technologies 17 Name Origin Description Huntsman Bath, UK Bitter Fuggles Wonderful hop, light alcohol, good summer beer Fragile; excessive variance pub to pub 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.

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20. Orgnizational and Distibuted Object Technologies 20 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;

21. Orgnizational and Distibuted Object Technologies 21 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/";

22. Orgnizational and Distibuted Object Technologies 22 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");

23. Orgnizational and Distibuted Object Technologies 23 // 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(""); }

24. Orgnizational and Distibuted Object Technologies 24 D:\McCarthy\www\95-733\examples\chap04>java NamespaceExplore <mm6:GradeBook xml:lang="en" xmlns:mm6= "http://www.andrew.cmu.edu/~mm6"> 87.5 Output