Implementing RDQL in Rasqal - Structure

• Query syntax parsing into...
• Abstract query construct made from sequences of:
  • source URIs (from)
  • binding variables (select)
  • triples to select (where)
  • constraint clauses
  • namespace / URI prefixes (expanded)
• Query construction/access API
• TripleSource(uri) interface providing...
• TriplesMatch(s,p,o) interface
• Factories for TriplesSource via Redland or Raptor (TODO)

RDQL / QL development

• Easy: Variable bindings
• (Easy: optional triples, one way - TODO)
• Medium: tokeniser and parser (lex and yacc)
• Medium: writing it in C
• Medium: query engine over TriplesMatch
• Medum, but dull: constraint evaluation
• (Medium: multiple sources - TODO)
• Hard: thinking about the APIs
• Hard: planning for future QLs, functionality

RDQL surprises and issues

• Jena RDQL Test suite tests beyond the RDQL note EBNF
• There are 4 pre-defined prefixes and namespaces
• xsd:integer and xsd:double in RDF typed literals
• UTF-8, \uHHHH in prefixes, local names (TODO)
• Are blank nodes allowed in queries?
• Multiple sources
• Constraint expressions still too rich
• Not using xsd:boolean, xsd:string
• select * vs no select