1. what is XML?
o       XML stands for Extensible Markup Language
o       It is a meta-markup language (you make up your own tags)
o       XML is not a programming language, it is a data format
o       XML documents can be parsed.
  
2. What is the difference between XML & HTML?
o       XML describes data, HTML displays data.
o       HTML has predefined tags, in XML we define tags
o       HTML can be displayed on its own, XML cannot.
        The combination of XML and HTML is XHTML.
  
3. What is a "well-formed" document?
   The well formed document must obey the basic XML constraints like :
o       All Documents must have a prolog.
o       Document must have a root tag.
o       All begin-tags must have end-tags. (case sensitive)
o       All attribute values must be quoted.
o       Elements must be properly nested.
o       All entities must be declared.
   If a document is not a well-formed document it is not a XML document.
  
4. What is DTD?
Document Type Definition defines the structure of an XML document. A DTD can
be declared inline in your XML document, or as an external reference.
DTD defines :
o       What element (tag) names are allowed
o       What attributes are used with each element
o       Which child elements belong to which parent elements
o       What order child elements can appear in
o       Also declares entities and notations
  
5. What are the building blocks of XML?
o       Elements
o       Attributes
o       Entities
o       Notations
  
6. What is a valid document
      If a document's structure and tag names match the information model, it
is 'valid'. Validation is optional. A valid document is always well-formed.
  
7. What is XSLT?
XSLT is a language for transforming the structure of XML documents. The XSL
Transformations (XSLT) vocabulary provides a rule-based framework for select
ing and processing document content, and transforming it into new documents
  
8. What is XML Parser?
A set of software components designed for reading, processing and creating X
ML documents.
Parsers expose the structures and tags within a XML document thus making it
easy to process XML documents.
  
9. What are the types of Parsers
DOM Vs SAX
o       SAX is event-based and DOM is object-based
o       SAX is developed by XML-Dev mailing list and DOM is a W3C recommendation
o       DOM constructs a tree in memory and SAX does not
o       SAX is read-only and DOM is read-write.
o       SAX uses less memory and is fast & efficient

        We also have Validating and non-validating parsers.
  
10. What is XML family ?
o       Display : XHTML, XSLT, XSL
o       Modeling : DTD, XML Schema
o       Manipulating : DOM, SAX
o       Querying : Xlink, XQL, Xpath

使用dom4j解析XML 把数据转换成XML格式的好处

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