XML (Extensible Markup Language)

A structured formatting language for marking up text data for them to be transported around the internet.

• Property
  • Self-describing
  • Not a programming language
  • Cannot display data
  • Tags not predefined
• Requirements
  • Should be well-formed
    • Correct syntax
    • Tags match
    • Tags nested
    • Characters legal
  • Should be valid according to DTD (Document Type Definition)
    • Tags used correctly
    • Tags all declared
    • Attributes all declared

Basic Syntax

<?xml version="1.0" ?>
<!DOCTYPE doctype [
    <!-- declarations -->
    <!ELEMENT element (nested)>
    <!ELEMENT nested type>
    <!ATTLIST element
        attr type value>
]>
<doctype>
    <element attr="attribute">
        <nested>text &entity;</nested>
    </element>
</doctype>

• Elements
  • Text
    • <text>text</text>
  • Empty
    • <empty/>
  • Attributes
    • <element attr="attribute">...
    • Easier than using tags to get any component, or change format, etc.
• Entities: symbols replaced by other text before displayed

Document Type

Describes the schema of an XML document. Can be viewed as a node-labeled tree.

• W3C recommendation
  • Elements and attributes that can appear
  • Which elements are child elements
  • Data types
• DTD
  • Verifies correctness
  • Describes format
  • Sharable
  • Standard or user-defined
• Examples
  • Technical report
  • Novel
  • Software manual
  • etc.

Standard Document Types

• Text
  • TEI, DocBook, NITF
• Data
  • CML, AIML
• Mixed
  • Often custom e.g. bug reports

Twig Pattern Query

Returns answers that match the structure of the XML document.

Given a twig query $$q$$ and XML document $$d$$, a match is a set of nodes $$n_1, \dots, n_k$$ s.t.

1. $$n_i$$ has the same label as the i-th element in $$q$$
2. The edge relationships are satisfied

• Edge
  • /: parent-child
  • //: ancestor-descendant