XML Interview Questions-1

11. Why is XML such an important development?
It removes two constraints which were holding back Web developments:
1. Dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;
2. The complexity of full SGML, whose syntax allows many powerful but hard to- program options.
3. XML allows the flexible development of user-defined document types. It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and data both on and off the Web; and it removes the more complex options of SGML, making it easier to program.

12.Is it possible to write the contents of org.w3c.dom. Document object into an .xml file?
Yes its possible. One to achieve this is by using Xerces. Xerces is an XML parser. You would use the following code
org.apache.xml.serialize.OutputFormat format = new org.apache.xml.serialize.OutputFormat(myDocument);
org.apache.xml.serialize.XMLSerializer output = new org.apache.xml.serialize.XMLSerializer(new FileOutputStream(new File("test.xml")), format);
output.serialize(myDocument);

13.What is the difference between DOM and SAX? What would you use if an option is given?
DOM parses an XML document and returns an instance of org.w3c.dom.Document. This document object's tree must then be "walked" in order to process the different elements. DOM parses the ENTIRE Document into memory, and then makes it available to you. The size of the Document you can parse is
limited to the memory available. SAX uses an event callback mechanism requiring you to code methods to handle events thrown by the parser as it encounters different entities within the XML document. SAX throws events as the Document is being parsed. Only the current element is actually in memory, so there is no limit to the size of a Document when using SAX. The specific parser technology that will be used will be determined by the requirements of your application. If you need the entire document represented, you will most likely use DOM builder implementation. If you only care about parts of the XML document and/or you only need to parse the document once, you might be better served using SAX implementation.

14. What is SOAP?
The Simple Object Access Protocol (SOAP) uses XML to define a protocol for the exchange of information in distributed computing environments. SOAP consists of three components: an envelope, a set of encoding rules, and a convention for representing remote procedure calls.

15. What is DOM?
The Document Object Model (DOM) is an interface specification maintained by the W3C DOM Workgroup that defines an application independent mechanism to access, parse, or update XML data. In simple terms it is a hierarchical model that allows developers to manipulate XML documents easily.

16. Can you walk us through the steps necessary to parse XML file?
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
DocumentBuilder domBuilder = factory.newDocumentBuilder();
Document doc = domBuilder.parse(XMLFile);

17. Is it necessary to validate XML file against a DTD?
Although XML does not require data to be validated against a DTD, many of the benefits of using the technology are derived from being able to validate XML documents against business or technical architecture rules.

18. What is XPath?
XPath stands for XML Path Language. XPath is a syntax for defining parts of an XML document. XPath is used to navigate through elements and attributes in an XML document XPath contains a library of standard functions. XPath is a major element in XSLT. XPath is designed to be used by both XSLT and XPointer
XPath is a W3C Standard.

19. What is XSL?
XSLT - a language for transforming XML documents. XSLT is used to transform an XML document into another XML document, or another type of document that is recognized by a browser, like HTML and XHTML. Normally XSLT does this by transforming each XML element into an (X)HTML element.

20. What is a DTD and a Schema?
The XML Document Type Declaration contains or points to markup declarations that provide a grammar for a class of documents. This grammar is known as a document type definition or DTD. The DTD can point to an external subset containing markup declarations, or can contain the markup declarations directly in an internal subset, or can even do both.

XML Schemas express shared vocabularies and allow machines to carry out rules made by people. They provide a means for defining the structure, content and semantics of XML documents.
Schemas are a richer and more powerful of describing information than what is possible with DTD’s.