Extensible Markup Language (XML)
standard for data representation and exchange
document format similar to HTML
– tags describe content instead of formatting
also streaming format

Basic constructs
tagged elements (nested)
attributes
text

“Well-formed” XML
adheres to basic structural requirements
– single root element
– matching tags, proper nesting
– unique attributes with elements

test XML structure with XML parser
parsed XML: DOM, SAX

Displaying XML
as XML document
use XSL (extensible stylesheet language) or CSS

Relational Model vs. XML

	relational	xml
structure	tables	hierarchical tree
schema	fixed in advance	flexible, “self-describing”
queries	simple langs	less so
ordering	unordered	implied ordering
implementation	native	add-on