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At the DAML PI meeting in April, program manager Murry Burke asked all principal investigators to convert their projects and Ontologies from DAML+OIL to OWL. At BBN we have a number of tools and Ontologies developed for the DAML program and hosted on www.daml.org. This document records our experiences and some lessons learned in the conversion to OWL.

• Conversion of OWL Ontologies and Instance Files
• Ontology and Instance Files: Lessons Learned
• OWL Tools and Agents
• Next Steps
• Download OWL Converter

BBN has updated the OWL conversion script from MindSwap.org to include more changes and to work with a larger variety of input files. We tested it by converting all the DAML+OIL files on http://www.daml.org (about 100 Ontologies and 1100 instance files). By the end of the process the script was able to convert most files completely. The updated OWL Conversion script is available for downloading, and can be run on computers with PERL installed. We also sent a copy to MindSwap.org so they can update the online version.

Items OWL Converter does not handle:

• Input files that do not contain line breaks are not converted correctly.
• It does not convert statements with literal values to the use of rdf:datatype attribute.

After conversion we used the standalone version of the OWL Validator to validate the ontology and instance files. Based on the results we were able to correct most of the remaining problems by hand.

Remaining Issues:

• References to an external DAML+OIL files that have not been converted to OWL cannot be updated until the referenced file is converted.
• The Validator uses a parser that does not recognize rdf:first, rdf:rest, rdf:nil tags, so it will produce parse errors even though the file is correct.

The following figure compares the results of the original OWL Conversion script and the modified OWL Conversion script to the final OWL Ontologies. The counts indicates the number of Ontologies with errors, warnings, or information messages after the conversion process. Files with parse errors were omitted from the remaining counts.

Validate Ontologies before validating artifact/instance/data files. When validating an instance file the OWL Validator will load the referenced Ontologies. If the referenced files contain errors or are not converted to OWL it could produce extra errors.

Specify an xml:base attribute in the RDF tag of your document. This will ensure the resources in the file will have a constant URI no matter what URI was used to load the file, including locally cached copies.

For example, [1a] and [1b] are two URLs for the same file. Loading them into Jena 1.6.1 using those two URLs will produce two different models (you can view the triples at [2a] and [2b]). In contrast, if we add an xml:base attribute to the file and load it into Jena 1.6.1 using the two different URIs [3a] and [3b] the models are identical (triples at [4a] and [4b]). You could even save the file locally on your computer and load it with a 'file:' URL and the URIs would remain consistent.

The value of xml:base could even be something completely different than the URI used to reference the file (eg. xml:base="http://www.nonexistantserver.org/example-ont.owl"), although we do not recommend this. It is preferable that the xml:base be a valid URL that resolves to the file for reasons of clarity (see additional comments below about the owl:Ontology and owl:imports tags).

[1a] http://www.daml.org/2003/06/owlConversion/examples/noxmlbase.owl
[1b] http://www.daml.org/2003/06/owlConversion/examples/noxmlbase
[2a] http://www.daml.org/2003/06/owlConversion/examples/noxmlbase.owl.out
[2b] http://www.daml.org/2003/06/owlConversion/examples/noxmlbase.out

[3a] http://www.daml.org/2003/06/owlConversion/examples/xmlbase.owl
[3b] http://www.daml.org/2003/06/owlConversion/examples/xmlbase
[4a] http://www.daml.org/2003/06/owlConversion/examples/xmlbase.owl.out
[4b] http://www.daml.org/2003/06/owlConversion/examples/xmlbase.out


If you wish to use OWL-DL or OWL-Lite, you can not use special OWL properties like owl:oneOf with rdf:Class. The domain of owl:oneOf is owl:Class. Though in OWL Full, rdf:Class and owl:Class are equivalent.

The URI of external Ontologies may change. If the Ontology depends on external Ontologies you may need to track down the OWL version of the ontology. The URI of that ontology may be different than the DAML version. It is also possible the referenced ontology will not be converted to OWL immediately, if at all.

If needed, an owl:Ontology tag can be used in instance files. Both ontology and instance files can contain an owl:Ontology declaration. The rdf:about attribute of the owl:Ontology tag should be the URL used to reference the file (traditionally rdf:about="" is used, which resolves to the base URL for the file). OWL includes a number of special properties to identify and manage Ontologies.

Include owl:imports statements for all Ontologies and instance files that are referenced in the file. This makes the dependencies on other files explicit. The imported URI should match the URI used in the owl:Ontology tag of the imported file, which should also be a valid URL for loading the file.

If you tool only works on instance files at the RDF level, then the tool probably already works with OWL (with the exception of rdf:datatype attributes).

For some tools it may be sufficient to replace the URIs for DAML+OIL terms with the URIs for the equivalent OWL (or RDF/RDFS) terms. See Appendix D of the OWL Reference for a list of most changes from DAML+OIL to OWL.

You may wish to limit your tool to work with one of the two subsets of the OWL language (OWL Species): OWL Lite or OWL-DL. See the OWL Reference documents for more information on OWL and the OWL Species.

• OWL Web Ontology Language Guide
• OWL Web Ontology Language Reference
• OWL Web Ontology Language Semantics and Abstract Syntax

We did not address the use of XML Datatypes in our OWL conversion. In particular the addition of rdf:dataype attributes to statements with literal values. One reason is the lack of support for rdf:datatype in Jena (version 1.x) and other tools. This would require a more complex conversion tool that would need to determine which data type to use based on ontology information, general heuristics, and human input.

The OWL Conversion script (BBN Modified Version) is available for download.

Requirements and Installation:

• The Perl scripting language needs to be installed on your computer.
• Download the owlConverter.pl script
• cgi-lib.pl must be in the same directory as owlConverter.pl
• Modify the first line of owlConverter.pl so it references perl on your computer.

Running owlConverter.pl:

owlConverter.pl inFile="file.daml" outFile="file.owl" defaultNs="namespace" defaultBase="base"

inFile is the file to convert.
outFile is where the converted file is saved.
defaultNs (optional) is a new default namespace (xmlns="") for the file.
defaultBase (optional) is a new default xml:base for the file.

owlConverter.pl will convert the inFile from DAML+OIL to OWL and write the file to outFile. If a defaultNs and/or defaultBase are specified the new values will be set as attributes in the rdf:RDF tag. The converter script will print the number of lines in the input file.

Authors

David Rager, Troy Self, and Jeremy Lerner.