Bootstrapping the Semantic Web
with Redland

Dave Beckett

Institute for Learning and Research Technology (ILRT),
University of Bristol, UK

Overview

• Semantic Web Development
• RDF in a Box
• Redland
• Requirements
• Features
• APIs and Querying
• Availability

What Is Redland?

Redland RDF Application Framework   Set of Libraries   Toolkit   Whatever!

RDF Technology in 2000

• Poor tool support:
  • 1 unmaintained fairly complete Java system
  • A few incomplete others
• RDF needed better tools
• Time to engineer something industrial strength
• New standards work was on the horizon
• Target users: web developers

RDF in a box

• Reliable, portable, flexible, ...ible
• Fast, efficient, small, ...
• Easy to use and program with
• Available in (insert your favourite language here)
• Web standards compliant
• Easy to use license

Summary: lowest possible barriers to use

Redland from Semantic Web @Bristol

The name: Redland is an area of Bristol, UK

FOAF was created here.

5 RDF W3C Recommendation editors work here.

Jena Java Semantic Web toolkit was created here at HP Labs.

(Actually Jena was created the same month as Redland, June 2000, by Brian McBride).

RDF in a box - Two Key Requirements

1. Portable to your system
2. Available in your programming language

Key Requirement 1 - Portable

• Answer: C
• Riposte: You are crazy, man!
• GNU autotools and libtool
• gcc -Weverything. g++ as a stricter C compiler
• Memory checkers such as dmalloc and valgrind(1)
• Unit tests, syntax tests, query tests
• SourceForge compile farm: ~9 unix / linux / OSX systems

Key Requirement 2 - Language Availability

• Answer: Simplified Wrapper and Interface Generator (SWIG)
• Language bindings to the major web development languages:
  Java, Perl, PHP, Python, Ruby, Tcl
• SWIG works best with C, less well with C++
• Non-answers: IDLs (Mozilla, CORBA, KDE/QT)
• Improve raw SWIG bindings with native metaphors (usability)
• Direct bindings: C# (Mono and .Net), Obj-C (OSX)

(Aside: I'm suspicious of any (web) technology that doesn't have easy to find and use software for it in a variety of languages)

Other Important Requirements

• Fast - C is close to the metal
• Small - minmality: do not create functionality in advance of needing it
• Modular - use whatever system functionality is available
• Configurable - GNU autoconf to choose modules and parts
• Minimal dependencies - just an XML parser
• Low memory use (no leaks), embeddable
• Web standards compliant
• Licence - LGPL / GPL / Apache2

API Style - Object-based C

• Object-based not Object-Orientated (OO)
• Constructors, destructors and methods reflected into C functions

    librdf_foo* librdf_new_foo(void);
    void librdf_free_foo(librdf_foo* foo);
    int librdf_foo_set_thing(librdf_foo* foo, char *thing);
    char *librdf_foo_get_thing(librdf_foo* foo);
  

• No garbage collecting at C level. Bindings should handle this.
• Classes and factories for multiple implemenations

    librdf_storage* a=librdf_new_storage("memory", ...);
    librdf_storage* b=librdf_new_storage("uri", ...);
  

• Gnome GLib could have been a choice here at the cost of a non-minimal set of dependencies

Data flow and constructs

• Reader pulls data
• Lazy evaluation
• No while loops (except query engine)
• Iterators for serializing objects, results
• Map to Perl @array, Python generators, C# Iterator ...
• Parser generates triples via callbacks

Semantic Web Stack

Tim Berners-Lee 2002

#include <stdweb.h>

	stdrdf
	stdxml
	stduri

C Open Source Web Libraries

(there is a libwww from the W3C but it covers a large range of web technologies, is rather monolithic and large and more a reference implementation)

Redland Components

• Raptor RDF Parser Toolkit (libraptor)
  Parsing, Serialising, URIs, WWW retrieval, Unicode and XML
• Rasqal RDF Query Library (librasqal)
  Query syntax support and execution engine
  (using Raptor)
• Redland (librdf)
  User API to all features and triple storage
  (using Raptor and Rasqal)
• Redland Bindings
  Language bindings to Redland
  (using Redland)

What you get in the Redland box

• RDF Input and Output to/from syntaxes (Raptor):
  RDF/XML, N-Triples, Turtle, RSS 1.0, RSS tag soup, Atom
• RDF triple Storage (Redland):
  Memory, File, URI, Sleepycat/BDB, MySQL, SQLite
• RDF API - RDF data access and manipulation (Redland):
  Graph and Triple APIs
• Language bindings (Bindings)
  C#, Java, Obj-C, Perl, PHP, Python, Ruby, Tcl
• Query languages and query engine (Rasqal):
  SPARQL and RDQL
• Command line utilities for Raptor, Rasqal and Redland

Redland Documentation

• Installation docs for each library
• News and detailed release notes for each library
• API reference (kerneldoc to DocBook) for Redland or manpages
• Manual pages for each utility and library
• Language bindings installation docs for each language
• POD for Perl. PyDoc for Python. RDoc for Ruby
• Missing: Tutorials
• Missing: Redland Book

Availability expectations

• Python - ship with the system
• Perl - be in CPAN
• PHP - if it doesn't ship with core PHP, very hard to convince
• Java - expect it to be pure Java (I lose)
• Ruby, Tcl - ?
• Linux, BSDen - packaged in RPM, deb, portage, ports, ...
• OSX - DMG packages and installers (and fink, darwinports)
• Windows - binaries with setup.exe

Availability to scripting languages

Expect to use it with one line of code

$ python
Python 2.3.4 (#1, Feb  2 2005, 12:11:53) 
[GCC 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
<<< import RDF
<<< 

Or none:

$ perl -MRDF::Redland '...'

You can always use the command line:

$ rdfproc
Redland RDF processor utility 1.0.0
Copyright (C) 2000-2005 David Beckett, ILRT, University of Bristol
Try `rdfproc --help' for more information.

Redland RDF APIs

• Manipulating triples and graphs
• Triple storage, Parsers, Serializers
• Tracking provenance and data aggregration
• Fine grained control
• Can be too low level

Alternatively, use a query language...

RDF Query in Redland - Rasqal

• RDQL - existing deployed language
• SPARQL - undergoing standardisation at W3C with new features
  • Managing aggregation
  • Better semi-structured data support
  • Turtle/N3 style triple syntax

RDF Query - SPARQL

• SPARQL Protocol and RDF Query Language
• A Query Language ...
  Find names and websites of contributors to PlanetRDF:

  PREFIX foaf: <http://xmlns.com/foaf/0.1/>
  SELECT ?name ?website
  FROM   <http://planetrdf.com/bloggers.rdf>
  WHERE { ?person foaf:weblog ?website ;
                  foaf:name ?name .
          ?website a foaf:Document
        }
  

• ... and a Protocol
  

  http://.../qps?
  query-lang=http://www.w3.org/TR/rdf-sparql-query/
  &graph-id=http://planetrdf.com/bloggers.rdf
  &query=PREFIX foaf: <http://xmlns.com/foaf/0.1/...
  

• Run this query (ex1.rq)

Redland Availability

• Source!
• RPMs and debs for libraries, Python, Perl and Ruby
• Linux: Ubuntu CD1. Raptor in SUSE and several others
• BSD ports in freshports
• Gentoo Linux emerge ports
• OSX Objective-C packages (3rd party)
• Win32 library DLLs, python, C# and ruby(soon) (3rd party)
• Used with some commercial applications
• Ruby gems (3rd party)
• Perl CPAN TODO old version

Demo

Demo

Parsing in raptor
GRDDL 1 or GRDDL 2

Querying in rasqal

Current and Future Possible Work

• Made it to V1.0 in less than 5 years
• Finishing SPARQL (current)
• SQLite store replacing Sleepycat (current)
• Free text searching
• Bug reports
• Redland (query) server, Apache mod_sparql?
• ...

For anything else, I prefer patches in diff -urN form :)

Thanks

Slides (will be linked from): http://purl.org/net/dajobe/

Redland: http://librdf.org/

Questions?

References

• The Design and Implementation of the Redland RDF Application Framework presented at the WWW10 conference, May 2001.