03 namespace
- 2. UNIT I INTRODUCTION TO XML XML document structure – Well formed and valid documents – Namespaces – DTD – XML Schema – X-Files.
- 3. XML Namespaces Provide a method to avoid element name conflicts
- 4. XML Namespaces • Multiple XML developers may choose the same element & attribute names for their standards – Each of them, may mean entirely different things. • For a processing application, to understand & associate the correct elements, – It must know which tag set the elements come from. • XML Namespaces provide a method to avoid element name conflicts. • Namespaces use a colon-delimited prefix To associate external semantics with elements – That can be identified via a Universal Resource Identifier (URI).
- 5. Example on XML Namespaces • For instance, this XML carries HTML table information : • Now, let’s look at another sample XML document – This XML carries information about a table (a piece of furniture): <table> <name>African Coffee Table</name> <width>80</width> <length>120</length> </table> <table> <tr> <td>Apples</td> <td>Bananas</td> </tr> </table>
- 6. • If these XML fragments were added together, – There would be a name conflict. • Both contain a <table> element, – But the elements have different content and meaning. • By using namespaces, – XML parsers can easily tell the difference b/w the two <table> elements. <h:table> <h:tr> <h:td>Apples</h:td> <h:td>Bananas</h:td> </h:tr> </h:table> <f:table> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length> </f:table> In this example, there will be no conflict because the two <table> elements have different names.
- 7. Declaring Namespaces • Namespaces can be declared using one of two methods: 1. A default declaration or 2. An explicit declaration.
- 8. A Default Declaration • A default namespace declaration Specifies a namespace to use for all child elements of the current element – That do not have a namespace prefix associated with them • Example : <Customer xmlns=”http://www.eps-software.com/po”> <Name>Travis Vandersypen</Name> <Order> <Product> <Name>Hot Dog Buns</Name> </Product> </Order> </Customer> Default declaration for the <Customer> element is defined by using the xmlns attribute All child elements of <Customer> element are specified as belonging to the “http://www.eps-software.com/po” namespace
- 9. An Explicit Declaration • This is similar to a default namespace declaration, – Except a prefix is associated with the xmlns attribute. • Example : A prefix “po” is with the elements within the document: <cust:Customer xmlns:cust=“http://www.eps-software.com/customer” xmlns:ord=“http://www.eps-software.com/order”> <cust:Name>Travis Vandersypen</cust:Name> <ord:Order> <ord:Product> <ord:Name>Hot Dog Buns</ord:Name> </ord:Product> </ord:Order> </cust:Customer> Two different namespaces are referenced: one for customers and one for orders. This allows a different set of rules to be applied for customer names versus product names.
- 10. Identifying the Scope of Namespaces • By default, – All child elements within a parent element appear within the parent’s namespace. • This allows – All child elements to “inherit” their parent element’s namespace. • The “inherited” namespace can be overwritten – By specifying a new namespace on a particular child element.
- 11. Identifying the Scope of Namespaces • Example: • <Customer> element declares a default namespace • <Order> element also declares a default namespace. • All unqualified elements within the <Order> element will inherit the namespace declared by the <Order> element. <Customer xmlns=“http://www.eps-software.com/customer”> <Name>Travis Vandersypen</Name> <Order xmlns=“http://www.eps-software.com/order”> <Product> <Name>Hot Dog Buns</Name> </Product> </Order> </Customer>