BD12 Querying

XML Navigation

Operator

• slash: /
• descendant axis : //
• attribute axis: @attr-name
• atomization: data(...)
• filter: [], e.g.@code[data(.)="CH"]
• parent abbreviation: /..
• collections: collection(...)
  Use . to represent the current element

JSON Navigation

• using . as the slash in XML.
• .countries is different from .countries[]
• using $$ to represent the current element.

Construction

• String Escaping
  • JSONiq: using the backslash: \",\n to replace quote, spare space.
  • XQuery: using "$#x000a; …
• Booleans
  • JSONiq: true, false
  • XQuery: true(), false()

Basic Operations

• Atomization: XML only: <a>42</a>+1=42+1=43
• Empty sequence: ()+1=()
• Cardinality: (3,4)+2: error
• General Comparison: =,<,>,>=,<=, but all the types must be the same
• Value Comparison: le,lt,eq, ne, ge, gt
• logics: conjunction, disjunction, not
• non-booleans
  • false: "", 0, ()
  • true: "foo", 42, (<foo/>,<bar/>,1,"foo")

    Architecture of a query processing engine

1. Parsing: from query to abstract syntax tree
2. translating: from AST to Expression tree
3. Optimization: Expression Tree
4. Code Generation: from Expression Tree to Iterator Tree

Further Reading

XQuery, 2nd Edition Chapter 2, 3, 4, 6, 7, 10, 11,