odML and RDF - Export and usage

Semantic Web and graph database searches

Searches within odML documents are part of the library implementation and imports from linked, external sources into odML documents can be easily done with the core library functionality. With the option to export odML documents to the RDF format, users also gain the option to search across multiple documents using tools from the Semantic Web technology.

If you are unfamiliar with it, we linked additional information to the Semantic web, RDF and SPARQL for your convenience and give the briefest introduction below.

RDF was designed by the World Wide Web Consortium (W3C) as a standard model for data representation and exchange on the web with the heterogeneity of data in mind. Even tough the RDF file format might vary, the underlying concept features two key points. The first is that information is structured in subject-predicate-object triples e.g. “apple hasColor red”. The second key point is that multiple subjects and objects can be connected to form a graph e.g. “tree hasFruit apple” can be combined with the previous example to form a minimal graph. These graphs can contain very heterogeneous data, but can still be queried using the SPARQL query language due to the semantic structure of the underlying data.

odML to RDF export

Without further ado the next sections will expose you to the range of odML to RDF features the core library provides. To check how to create a graph database from exported odML documents and how to query such a database please refer to the section below.

Default odML to XML RDF export

Once an odML document is available, it can most easily be exported to RDF by the odml.save feature.

Given below is a minimal example:

import odml

doc = odml.Document()
sec = odml.Section(name="rdf_export_section", parent=doc)
prop = odml.Property(name="rdf_export_property", parent=sec)

odml.save(doc, "./rdf_export.rdf", "RDF")

This will export the odML document to the RDF format in the XML flavor and will save it to the file ./rdf_export.rdf. The content of the file will look something like this (the UUIDs of the individual nodes will differ):

<?xml version="1.0" encoding="UTF-8"?>
  <rdf:Description rdf:about="https://g-node.org/odml-rdf#281c5aa7-8fea-4852-85ec-db127f753647">
    <rdf:type rdf:resource="https://g-node.org/odml-rdf#Property"/>
  <rdf:Description rdf:about="https://g-node.org/odml-rdf#08c6e31a-533f-443b-acd2-8e961215d38e">
    <odml:hasSection rdf:resource="https://g-node.org/odml-rdf#eebe4bf7-af10-4321-87ec-2cdf77289478"/>
    <rdf:type rdf:resource="https://g-node.org/odml-rdf#Document"/>
  <rdf:Description rdf:about="https://g-node.org/odml-rdf#eebe4bf7-af10-4321-87ec-2cdf77289478">
    <odml:hasProperty rdf:resource="https://g-node.org/odml-rdf#281c5aa7-8fea-4852-85ec-db127f753647"/>
    <rdf:type rdf:resource="https://g-node.org/odml-rdf#Section"/>
  <rdf:Description rdf:about="https://g-node.org/odml-rdf#Hub">
    <odml:hasDocument rdf:resource="https://g-node.org/odml-rdf#08c6e31a-533f-443b-acd2-8e961215d38e"/>

Specific RDF format export

The RDFWriter class is used to convert odML documents to one of the supported RDF formats:

xml, pretty-xml, trix, n3, turtle, ttl, ntriples, nt, nt11, trig

turtle is the format that is best suited for storage and human readability while for cross-tool usage, saving RDF in its XML variant is probably the safest choice.

The exported output can be returned as a string:

from odml.tools.rdf_converter import RDFWriter


This will print the content of the odML document in the Turtle flavor of RDF:

@prefix odml: <https://g-node.org/odml-rdf#> .

odml:Hub odml:hasDocument odml:08c6e31a-533f-443b-acd2-8e961215d38e .

odml:08c6e31a-533f-443b-acd2-8e961215d38e a odml:Document ;
    odml:hasFileName "None" ;
    odml:hasSection odml:eebe4bf7-af10-4321-87ec-2cdf77289478 .

odml:281c5aa7-8fea-4852-85ec-db127f753647 a odml:Property ;
    odml:hasName "rdf_export_property" .

odml:eebe4bf7-af10-4321-87ec-2cdf77289478 a odml:Section ;
    odml:hasName "rdf_export_section" ;
    odml:hasProperty odml:281c5aa7-8fea-4852-85ec-db127f753647 ;
    odml:hasType "n.s." .

The output can of course also be written to a file with a specified RDF output format; the output file will autmatically be assigned the appropriate file ending:

from odml.tools.rdf_converter import RDFWriter

RDFWriter(doc).write_file("./rdf_export_turtle", "turtle")

All available RDF output formats can be viewed via odml.tools.parser_utils.RDF_CONVERSION_FORMATS.keys().

Bulk export to XML RDF

Existing odML files can be exported to XML RDF in bulk using the odmltordf command line tool that is automatically installed with the core library.

odmlToRDF searches for odML files within a provided SEARCHDIR and converts them to the newest odML format version and exports all found and resulting odML files to XML formatted RDF. Original files will never be overwritten. New files will be written either to a new directory at the current or a specified location.

Usage: odmltordf [-r] [-o OUT] SEARCHDIR

The command line option -r enables recursive search, -o OUT specifies a dedicated output folder for the created output files.

Advanced features

RDF subclassing of odml.Section.type

By default a set of pre-defined odml.Section.types will export Sections not as an odml:Section but as a specific RDF subclass of an odml:Section. This is meant to simplify SPARQL query searches on graph databases that contain odml specific RDF.

As an example an odml.Section normally gets exported as RDF class type odml-rdf:Section:

<rdf:type rdf:resource="https://g-node.org/odml-rdf#Section"/>

An odml.Section with the odml.Section.type=”protocol” will by default be exported as a different RDF class type:

<rdf:type rdf:resource="https://g-node.org/odml-rdf#Protocol"/>

In an RDF query this can now be searched for directly by asking for RDF class “odml-rdf:Protocol” instead of asking for RDF class “odml-rdf:Section” with type “Protocol”.

On install the core library already provides a list of odml.Section.type mappings to RDF subclasses. On initialisation the RDFWriter loads all subclasses that are available and uses them by default when exporting an odML document to RDF. The available terms and the mappings of odml.Section.types to RDF subclasses can be viewed by accessing the section_subclasses attribute of an initialised RDFWriter:

rdf_export = RDFWriter(doc)

This export also adds all used subclass definitions to the resulting file to enable query reasoners to makes sense of the introduced subclasses upon a query.

Currently the following mappings of odml.Section.type values to odml-rdf:Section subclass are available:

analysis: Analysis
analysis/power_spectrum: PowerSpectrum
analysis/psth: PSTH
cell: Cell
datacite/alternate_identifier: AlternateIdentifier
datacite/contributor: Contributer
datacite/contributor/affiliation: Affiliation
datacite/contributor/named_identifier: NamedIdentifier
datacite/creator: Creator
datacite/creator/affiliation: Affiliation
datacite/creator/named_identifier: NamedIdentifier
datacite/date: Date
datacite/description: Description
datacite/format: Format
datacite/funding_reference: FundingReference
datacite/geo_location: GeoLocation
datacite/identifier: Identifier
datacite/related_identifier: RelatedIdentifier
datacite/resource_type: ResourceType
datacite/rights: Rights
datacite/size: Size
datacite/subject: Subject
datacite/title: Title
dataset: Dataset
data_reference: DataReference
blackrock: Blackrock
electrode: Electrode
event: Event
event_list: EventList
experiment: Experiment
experiment/behavior: Behavior
experiment/electrophysiology: Electrophysiology
experiment/imaging: Imaging
experiment/psychophysics: Psychophysics
hardware_properties: HardwareProperties
hardware_settings: HardwareSettings
hardware: Hardware
hardware/amplifier: Amplifier
hardware/attenuator: Attenuator
hardware/camera_objective: CameraObjective
hardware/daq: DataAcquisition
hardware/eyetracker: Eyetracker
hardware/filter: Filter
hardware/filter_set: Filterset
hardware/iaq: ImageAcquisition
hardware/light_source: Lightsource
hardware/microscope: Microscope
hardware/microscope_objective: MicroscopeObjective
hardware/scanner: Scanner
hardware/stimulus_isolator: StimulusIsolator
model/lif: LeakyIntegrateAndFire
model/pif: PerfectIntegrateAndFire
model/multi_compartment: MultiCompartmentModel
model/single_compartment: SingleCompartmentModel
person: Person
preparation: Preparation
project: Project
protocol: Protocol
recording: Recording
setup: Setup
stimulus: Stimulus
stimulus/dc: DC
stimulus/gabor: Gabor
stimulus/grating: Grating
stimulus/pulse: Pulse
stimulus/movie: Movie
stimulus/ramp: Ramp
stimulus/random_dot: RandomDot
stimulus/sawtooth: Sawtooth
stimulus/sine_wave: Sinewave
stimulus/square_wave: Squarewave
stimulus/white_noise: Whitenoise
subject: Subject

Custom RDF subclassing

The default list of odml.Section.types can be supplemented or even replaced by custom type to RDF subclass mappings.

All required is to provide a dictionary of the format {"odml.Section.type value": "RDF subclass value"}. Please note that the odml.Section.type value should be provided lower case, while the RDF subclass value should be provided upper case:

custom_class_dict = {"species": "Species", "cell": "Neuron"}
rdf_export = RDFWriter(doc, custom_subclasses=custom_class_dict)

Please note that entries in a custom subclass dictionary will overwrite entries in the default subclass dictionary.

Disable RDF subclassing

The subclassing feature can be disabled to export all odml.Sections as plain odml-rdf:Sections instead. This might be necessary if for e.g. a graph database is used that does not provide proper SPARQL reasoning and cannot make sense of RDF subclasses:

rdf_export = RDFWriter(doc, rdf_subclassing=False)