RDF API Draft

Current revision: 2001-01-19

Overview
Known use cases
Download and revision history
Documentation (most recent release)
Ant build script for source code contributed by David Li (DigitalSesame.com)
FAQ (incomplete)
Tutorial (under construction)
Examples
Creating unique URIs
Vocabulary class generator
Cryptographic digests of RDF models and statements
UML on top of RDF (code included in this distribution)
Feedback

Overview

This is a draft of an RDF API provided for a public discussion. The API defines interfaces for parsing (org.w3c.rdf.syntax) and accessing RDF models as sets of statements (org.w3c.rdf.model). Default implementations for those interfaces are included in the org.w3c.rdf.implementation package.

There are additional modules in the distribution that do not belong to the core API. They are packaged with the API to simplify download and evaluation:

Since May 12, 2000 the distribution includes
- support for UML over RDF
- a tool for generating classes with Java "constants" for simplified manipulation of schemas (edu.stanford.db.rdf.vocabulary.Generator, details here)
Since Dec 16, 1999 the distribution includes a parser for a simplified syntax for RDF. See "Briding the Gap between RDF and XML" and "Simplified Syntax for RDF" for more details.

Known use cases

Protégé 2000 by Stanford Medical Informatics
Promenade RDF Parser by Profium
FRODO RDFSViz by DFKI Kaiserslautern
OntoEdit by AIFB Karlsruhe University / OntoPrise
Interdataworking Converter
CIMValidate by Arnold deVos (Langdale Consultants)
DAMLJessKB by Joe Kopena

Please let me know about further uses.

Download and revision history

.zip files contain documentation, sources and the jar file.

2001-01-19	Download: rdf-api-2001-01-19.zip (jar file only) Optimization release. Speed-up by an order of magnitude when dealing with large models. Provided a more efficient implementation of interfaces in `org.w3c.rdf.model` (i.e. resources, statements, models etc.) The new implementation is contained in package `edu.stanford.db.rdf.model.i` and is used as the default one in examples and `org.w3c.rdf.util.RDFFactoryImpl`. Make sure you switch to the new implementation if you were using `org.w3c.rdf.implementation.model` classes directly (e.g. not via RDFFactory) in your code! Added a new pair of parser/serializer: `edu.stanford.db.rdf.syntax.generic.{TripleSerializer\|TripleParser}`. These are stream-oriented tools that are based on an extremely simple XML-based serialization syntax. The parser/serializer are very fast and small, and support a compact reification syntax. Use them e.g. for on-the-wire exchange of RDF models. Better namespace support: added capability of overriding the default way the namespace abbreviations are generated in the serializer SiRS. Added a group of methods `collectNamespaces` in `org.w3c.rdf.util.RDFUtil` (suggested by Michael Sintek). Fixed bug in saving of models in `RDFUtil` (uncovered by Michael Sintek). Added method `getNodeFactory` to `RDFFactory`.
2000-12-05	Download: rdf-api-2000-12-05.zip (jar file only) Bugfix release. Made digest computation in the default resource/literal/model implementation more efficient Implemented syntax in `edu.stanford.db.rdf.syntax.generic.TripleSerializer`. Now it supports reification and embedded models efficiently SiRS: fixed "order"-related bug; revived abbreviated syntax; improved efficiency SiRPAC: added a function to disable fetching of external entities in XML parser; fixed bug with empty name in input source
2000-11-13	Download: rdf-api-2000-11-13.zip (jar file only) This release contains a major package restructuring; the `org.w3c.rdf` subtree has been cleaned up, a few packages have been moved to `edu.stanford` tree. The API interfaces are not affected. In addition, this release provides several fixes and improvements. Moved `org.w3c.rdf.util.xml` to `edu.stanford.db.xml.util` and `edu.stanford.db.rdf.syntax.generic` Moved `org.w3c.rdf.implementation.syntax.strawman` to `edu.stanford.db.rdf.syntax.strawman` Moved `org/w3c/rdf/examples/StrawmanToMS10.java` to `edu/stanford/db/rdf/examples/StrawmanToMS10.java` Modified SiRPAC to reflect changes Moved digest utilities from `org/w3c/rdf/util/` to `org/w3c/rdf/digest/` Trashed `org/w3c/rdf/util/OrderUtil.java`, `org/w3c/rdf/util/OrderedModel.java` Trashed `org/w3c/tools` completely Generated an updated schema vocabulary `org/w3c/rdf/vocabulary/rdf_schema_200001/RDFS.java` Generated a schema vocabulary for DAML-O: `edu/stanford/db/rdf/vocabulary/daml_o_20001011/DAML_O.java` Fixed a bug in SiRS serializer which could not deal with more than 26 namespaces (reported by Mike Dean). Modified the digest algorithm for models as suggested by Steve Dunham. The algorithm is now cryptographically secure.
2000-10-30	Download: rdf-api-2000-10-30.zip (jar file only) Notice: this release contains (incremental) changes to the API that are not backward compatible! Now resources support methods `getNamespace()` and `getLocalName()`. This change affected several other interfaces. Changed `NodeFactory` interface: allow namespace-based resource creation Changed `ModelImpl` (fixed bug in duplication of models) Added `getName` and `getNamespace` to `RDFUtil` Extended `NodeFactory` to `createLiteral`s for all primitive Java types: boolean, byte, short, char, int, long, float, double Modified `NodeFactory` implementation to speedup secure random generation Fixed a bug in SiRS related to empty namespaces `ParseAndSerialize` accepts options `-xml` and `-triples` Moved experimental order resources to a separate class (`edu.stanford.db.rdf.vocabulary.order_20000527`) and changed SiRPAC and SiRS adequately. Added more reserved words to `edu.stanford.db.rdf.vocabulary.Generator` SiRPAC now recognizes unqualified `ID`, `resource` and `about` XML attributes. It also supports new namespace handling and deals with string generation in a slightly more efficient way. Fixed bug in SiRPAC related to explicit use of ordinals `rdf:_1` etc. Added a new example, a tiny utility that generates unique resource identifiers (`org.w3c.rdf.examples.CreateUniqueURIs`)
2000-09-03	Download: rdf-api-2000-09-03.zip (jar file only) Bugfix release, 100% contributed by William Grosso. No changes in the API. Fixed bug that prevented source code from being compiled properly Replaced package `org.w3c.rdf.implementation.model` by more efficient code provided by Bill (from now on, Java 1.2+ is required) Serializer (`org.w3c.rdf.implementation.syntax.sirpac.SiRS`) now generates correct syntax for class names that contain spaces
2000-05-12	Download: rdf-api-2000-05-12.zip (jar file only) latest release that worked with Java 1.1.x; newer releases require Java 1.2+ added support for RDF schema: `edu.stanford.db.rdf.schema.RDFSchemaModel` (includes validation) added support for UML over RDF: `edu.stanford.db.rdf.uml.UMLModel` (includes validation) generated vocabulary classes for DublinCore, UML Core, StateMachines, DataTypes, Behavior experimental support for order by reification. Methods for ordering are in `org.w3c.rdf.util.OrderUtil`. (added support for `rdf:order` and `rdf:backwardOrder` to SiRPAC) improved SiRS (serializer), uses entities to generate compact syntax (also support for order) minor bugfixes in SiRPAC fixed the security bug in the statement digest algorithm (reported by Brian McBride). Model digest is still insecure. added exceptions to the core interfaces (`org.w3c.rdf.model.ModelException`) added method `isEmpty()` to model added `createOrdinal()` to `NodeFactory`, removed `ord()` from `RDFUtil` changed `RDFConsumer`: `addStatement()` receives a statement as a parameter instead of (s, p, o) added `isMutable()` to `Model` made vocabularies be classes instead of interfaces. A `NodeFactory` that creates custom resources can now be set using a static method
2000-04-13	Download: rdf-api-2000-04-13.zip (jar file only) Contains improvements proposed by Stefan Haustein: Reorganized the package structure: `org.w3c.rdf.model.impl.ModelConsumer -> org.w3c.rdf.util.ModelConsumer org.w3c.rdf.syntax.xml -> org.w3c.rdf.util.xml org.w3c.rdf.model.impl -> org.w3c.rdf.implementation.model org.w3c.rdf.syntax.* -> org.w3c.rdf.implementation.syntax.*` Added `NodeFactory` interface to `org.w3c.rdf.model` and updated `RDFConsumer`. Now the parsers can create custom RDF nodes during parsing. Updated the strawman parser: now it starts interpreting XML as RDF only when it encounteres one of the attributes `rdf:instance`, `rdf:for`, or `rdf:resource`. triples of the kind `(X, rdf:type, rdfs:Resource)` are filtered out before passing to `RDFConsumer`
1999-12-18	Download: rdf-api-1999-12-18.zip (jar file only) SHA-1 algorithm (160-bit hash) is now used by default instead of MD5 (128-bit) to compute the URIs for reified statements, models and anonymous resources.
1999-12-16	Download: rdf-api-1999-12-16.zip (jar file only) Classes `org.w3c.rdf.model.Triple` and `org.w3c.rdf.model.RDFModel` have been renamed into `org.w3c.rdf.model.Statement` and `org.w3c.rdf.model.Model` respectively. Strawman parser package added: `org.w3c.rdf.syntax.strawman` Generic RDF/XML parser package added: `org.w3c.rdf.syntax.xml` Minor bug fixes
1999-12-06	Download: rdf-api-1999-12-06.zip (jar file only) Original preview package

Examples

Some examples are contained in the package org.w3c.rdf.examples. Please use them to familiarize yourself with the API. Run

java org.w3c.rdf.examples.ParseAndSerialize

to list the command line parameters of this tool.

Vocabulary class generator

All vocabulary classes (RDF, RDFS, DC etc) included in the distribution were generated using this utility.

Examples:

java edu.stanford.db.rdf.vocabulary.Generator
  -s http://www.w3.org/1999/02/22-rdf-syntax-ns#
  -o org.w3c.rdf.vocabulary.rdf_syntax_19990222.RDF

java edu.stanford.db.rdf.vocabulary.Generator
  -n http://www.w3.org/2000/01/rdf-schema#
  -s http://www.w3.org/2000/01/rdf-schema
  -o org.w3c.rdf.vocabulary.rdf_schema_200001.RDFS

java edu.stanford.db.rdf.vocabulary.Generator
  -s http://www-db.stanford.edu/~melnik/rdf/vocabulary/dublin-core-19990702.rdf
  -o org.w3c.rdf.vocabulary.dublin_core_19990702.DC
  -n http://purl.org/dc/elements/1.1/

Creating unique URIs

Sometimes there is a need to generate a unique identifier for a resource that does not inherently have a URI e.g. a person. A list of unique resource identifiers (URIs) can be created as follows:

java org.w3c.rdf.examples.CreateUniqueURIs [<number of URIs>]

Cryptographic digests of RDF models and statements

The default implementation of the API interfaces supports computing cryptographic digests of models and statements. This approach provides a straightforward way of digital signing of RDF content (as opposed to signing of serialized RDF), facilitating the "Web of Trust". URIs of statements and models are based on their digests.

Standard SHA-1-based cryptographic digests are used in the algorithm. The digest algorithm for a statement with subject s, predicate p and object o is:

  d1 = SHA1(s)
  d2 = SHA1(p)
  d3 = SHA1(o)

  if(o instanceof Literal)
    rotate left d3 by 8 bits

  statement_digest = SHA1( concat(d1, d2, d3) )

The digest algorithm for models (suggested by Steve Dunham) is

  model_digest = SHA1( concat( sort( statment_digests )))

The statement digests are introduced to the SHA1 algorithm sorted bytewise in an increasing order. The digests of URIs and literals are computed over UTF-8 encoded strings.

Feedback

To: Sergey Melnik
Cc: www-rdf-interest@w3.org