1. Jennifer Widom XML Data DTDs, IDs & IDREFs

2. Jennifer Widom DTDs, IDs & IDREFs “Well-Formed” XML Adheres to basic structural requirements Single root element Matched tags, proper nesting Unique attributes within elements

3. Jennifer Widom “Valid” XML Adheres to basic structural requirements  Also adheres to content-specific specification Document Type Descriptor (DTD) XML Schema (XSD) DTDs, IDs & IDREFs

4. Jennifer Widom “Valid” XML Adheres to basic structural requirements  Also adheres to content-specific specification XML Parser XML Parser XML Document XML Document Parsed XML “Not well-formed” DTDs, IDs & IDREFs

5. Jennifer Widom “Valid” XML Adheres to basic structural requirements  Also adheres to content-specific specification Validating XML Parser Validating XML Parser XML Document XML Document “Not well-formed” DTD or XSD DTDs, IDs & IDREFs

6. Jennifer Widom “Valid” XML Adheres to basic structural requirements  Also adheres to content-specific specification Validating XML Parser Validating XML Parser XML Document XML Document Parsed XML “Not valid” DTD or XSD DTDs, IDs & IDREFs

7. Jennifer Widom Document Type Descriptor (DTD)  Grammar-like language for specifying elements, attributes, nesting, ordering, #occurrences  Also special attribute types ID and IDREF(S) DTDs, IDs & IDREFs

8. Jennifer Widom DTD/XSD versus none (well-formed) + DTD/XSD - DTD/XSD DTDs, IDs & IDREFs