The RDF Toolkit is a 'swiss army knife' tool for reading and writing RDF files in multiple formats.
The primary reason for creating this tool was to have a reference serializer for the FIBO ontologies as they are stored in Github FIBO repository. However, the tool is not in any way specific to FIBO, and it can be used with any ontology or RDF file. In this capacity, it can be used in a commit-hook to make sure that all RDF files in the repo are stored in the same way.
For the purposes of git-based version control of ontology files, we want to have as few differences between commits as possible. Most ontology editors can encode RDF graphs, including OWL ontologies, in several formats, including the W3C normative RDF exchange formats (syntaxes): RDF/XML and Turtle. However, even these normative formats are not canonical. Therefore, an editor tool may change many aspects of how ontology entities are serialized every time the ontology is saved (such as adding/changing comments or changing the order and organization of statements) leading to difficulties in analyzing actual changes in the underlying semantics.
We want to be able to include actionable information as part of IRIs, e.g., git tags, and then deference them from ontology tools like Protege.
The recommended output format at this time is RDF/XML because that is the format that the OMG requires for submissions.
The EDM Council develops the FIBO Ontologies and submits them as RDF/XML, serialized by the RDF Toolkit to the OMG.
So that is why we also use RDF/XML in Github itself.
To run RDF Toolkit one needs JAVA JRE installed version 11+.
Download the RDF Toolkit binary from here.
One can use RDF Toolkit as a standalone application, which can be run from the command line, or as a part of the git commit mechanism.
You can use RDF Toolkit to serialize any RDF file to a required format whether it is inside a version controlled folder or not. To find its current options, run this command in your operating system's command-line interface (e.g., Terminal in Linux and Mac OS, Command Shell in Windows, etc.):
java -jar rdf-toolkit.jar --help
For instance, if you want to serialise an RDF/XML file 'example.rdf', which is located in C:/source_ontologies/ folder into a Turtle file 'example.ttl' in C:/serialised_ontologies/ folder, you may use the following command:
java -jar rdf-toolkit.jar --source C:/source_ontologies/example.rdf --target C:/serialised_ontologies/example.ttl --infer-base-iri
-bi,--base-iri <arg> set IRI to use as base URI
-dtd,--use-dtd-subset for XML, use a DTD subset in order to allow prefix-based
IRI shortening
-h,--help print out details of the command-line arguments for the
program
-i,--indent <arg> sets the indent string. Default is a single tab character
-ibi,--infer-base-iri use the OWL ontology IRI as the base URI. Ignored if an
explicit base IRI has been set
-ibn,--inline-blank-nodes use inline representation for blank nodes. NOTE: this will
fail if there are any recursive relationships involving
blank nodes. Usually OWL has no such recursion involving
blank nodes. It also will fail if any blank nodes are a
triple subject but not a triple object.
-ip,--iri-pattern <arg> set a pattern to replace in all IRIs (used together with
--iri-replacement)
-ir,--iri-replacement <arg> set replacement text used to replace a matching pattern in
all IRIs (used together with --iri-pattern)
-lc,--leading-comment <arg> sets the text of the leading comment in the ontology. Can
be repeated for a multi-line comment
-ln,--line-end <arg> sets the end-line character(s); supported characters: \n
(LF), \r (CR). Default is the LF character
-osl,--override-string-language <arg> sets an override language that is applied to all strings
-oxn,--omit-xmlns-namespace omits xmlns namespace
-s,--source <arg> source (input) RDF file to format
-sd,--source-directory <arg> source (input) directory of RDF files to format. This is a
directory processing option
-sdp,--source-directory-pattern <arg> relative file path pattern (regular expression) used to
select files to format in the source directory. This is a
directory processing option
-sdt,--string-data-typing <arg> sets whether string data values have explicit data types,
or not; one of: explicit, implicit [default]
-sfmt,--source-format <arg> source (input) RDF format; one of: auto (select by
filename) [default], binary, json-ld (JSON-LD), n3, n-quads
(N-quads), n-triples (N-triples), rdf-a (RDF/A), rdf-json
(RDF/JSON), rdf-xml (RDF/XML), trig (TriG), trix (TriX),
turtle (Turtle)
-sip,--short-iri-priority <arg> set what takes priority when shortening IRIs: prefix
[default], base-iri
-sni,--suppress-named-individuals suppresses all instances of owl:NamedIndividual
-t,--target <arg> target (output) RDF file
-tc,--trailing-comment <arg> sets the text of the trailing comment in the ontology. Can
be repeated for a multi-line comment
-td,--target-directory <arg> target (output) directory for formatted RDF files. This is
a directory processing option
-tdp,--target-directory-pattern <arg> relative file path pattern (regular expression) used to
construct file paths within the target directory. This is
a directory processing option
-tfmt,--target-format <arg> target (output) RDF format: one of: json-ld (JSON-LD),
rdf-xml (RDF/XML), turtle (Turtle) [default]
-udl, --use-default-language <arg> default language tag for untyped, untagged strings
-v,--version print out version details
You can use RDF Toolkit as a built-in serialization tool that is launched each time you add a commit to your local Git repository. This will guarantee that every commit you do will re-write your RDF/OWL files in a consistent way that can be compared and merged with work done by other FIBO collaborators.
Actually, in order to use this RDF Toolkit in this capacity, you will also need a pre-commit file.
You need to copy these two files:
- pre-commit (no file extension)
- rdf-toolkit.jar
to the .git/hooks/ folder inside your local Git repository. The example below shows the location of this folder in a local Git repository for FIBO:
Make sure that:
- you have set the environment variable JAVA_HOME to the location of your Java
- if you have not because you don't know how to do it, ask uncle Google, e.g., by visiting https://www.baeldung.com/java-home-on-windows-7-8-10-mac-os-x-linux
- if you want to point the
RDF Toolkitto a different Java version, uncomment the following line in the pre-commit file pointing to the required path:# export RDF_TOOLKIT_JAVA_HOME=<path_to_java>
- name of the pre-commit file is just 'pre-commit' - your file browser might want to append a suffix like .txt to it
- you update these files from time to time since they both may be changed
- in an *nix-similar system (e.g., Linux, macOS, etc.) you may need to make the pre-commit file executable - see, for example, https://www.warp.dev/terminus/chmod-x.
- if the file gets quarantined, you may need to follow this hint https://stackoverflow.com/a/60082378/2596664.
You don't have to do anything to run RDF Toolkit in this mode because every commit in Git will start it for you.
When it runs properly, you should be able to see in your git console messages that look like the ones below:
rdf-toolkit: sesame-serializer: This is the pre-commit hook
rdf-toolkit: sesame-serializer: java_home = /Library/Java/JavaVirtualMachines/jdk-16.0.1.jdk/Contents/Home/
rdf-toolkit: sesame-serializer: whichJava = /Library/Java/JavaVirtualMachines/jdk-16.0.1.jdk/Contents/Home//bin/java
rdf-toolkit: sesame-serializer: Found rdf-toolkit: /***/.git/hooks/rdf-toolkit.jar
rdf-toolkit: sesame-serializer: Launching the sesame-serializer with --source DE/CarControl.rdf
...
+ rc=0
+ set +x
rdf-toolkit: sesame-serializer: Re-adding potentially re-serialized file to git staging area: VC/VehicleParts.rdf
[auto-83_missing_definitions d6f582e] more changes after review of definitions
3 files changed, 17 insertions(+), 17 deletions(-)
To ensure that an ontology is always serialized in the same manner, the serialization algorithm has been implemented in the RDF Toolkit. The following description attempts to give a short overview of this algorithm.
Serialization has three consecutive stages:
- Serialization of the header
- Triples' serialization
- Serialization of the footer
This depends on the type of the serialization format, e.g. in the case of RDF/XML, the XML starting tag is used followed by the DTD declaration (if it is enabled).
Then all namespaces are written alphanumerically.
Optionally, leading comments are serialized.
First, we write triples whose subject is the ontology, including "import triples", and then all other triples - starting with the subset of those that do not contain blank nodes.
As a rule, all triples are sorted as follows:
- First, we sort all triples by their subjects.
- Then, within each set of triples with the same subject, we sort by predicates.
- Finally, within each set of triples with the same subject and predicate, we sort by objects.
This sorting of triples presupposes that all resources within an ontology are sorted first.
- By default, all resources are sorted alphanumerically - with the following exceptions:
- All blank nodes come after IRIs.
- All RDF collections come before any other blank node.
- Serialization names for blank nodes are prepared using the pattern
blankXXX, whereXXXrepresents the ordinal number of the given blank node, e.g.001,010,999. The number ofXs in this pattern is based on the number of blank nodes.
This part depends on the serialisation used, e.g., in the case of RDF/XML it is one line:
</rdf:RDF>