EMF resource for RDF graphs

This repository includes a prototype implementation of an EMF resource for RDF graphs, on top of Apache Jena.

It can be installed from the repository's update site: see below for details. It is also available as a Maven artifact.

This RDF-EMF resource produces an EMF model representation of an RDF model; this could be an EMF model saved as RDF, or an RDF model from another program. One or more RDF model files and schemas can be combined/reasoned before being deserialised against an EMF Ecore metamodel. An EMF model instance is composed of EObjects for the RDF model element that have rdf:type statements that match an EClass in the configured Ecore metamodel(s).

The repository includes a read-only Epsilon Model Connectivity driver as well.

Installation

Eclipse IDE

Install the features from this update site:

https://epsilonlabs.github.io/emf-rdf/updates/

Alternatively, you can download a zipped version of the update site.

Example projects are available from the examples folder of this repository.

Maven

The EMF resource is available as a Maven dependency from Github Packages:

<dependency>
  <groupId>org.eclipse.epsilon</groupId>
  <artifactId>org.eclipse.epsilon.rdf.emf</artifactId>
  <version>1.0.0-SNAPSHOT</version>
</dependency>

Differences with emf-triple

This implementation has some major differences with emf-triple:

• A single resource can combine information from multiple sources (e.g. Turtle or RDF/XML files).
• OWL inference is supported.

These differences are achieved by loading an intermediary .rdfres file with all the data and schema models to be combined, as well as any relevant options.

Current limitations

Saving has only been tested against file-based locations. We have not tested saving into triple stores.

The resource assumes that the EPackage nsURI and the RDF nsURI used for rdf:type subjects and for property statements (e.g. metamodel:featureName) are a close match to each other. Specifically, we support two options:

• RDF namespace IRI = EPackage nsURI (including any trailing separator, such as # or /).
• RDF namespace IRI = EPackage nsURI + "#".

Namespaces for creating EMF models must be configured in the .rdfres (see Default model namespace section below). At the moment, the same namespace URI is used for every EObject created by the resource.

The contents of the resource must only be changed after it has been loaded. The resource assumes that a Jena graph is present to be synchronised whenever a change is made to the contents of the resource.

.rdfres file format

Suppose you have a model.ttl Turtle file with some statements of interest, written against an ontology in schema.ttl.

Suppose as well that the RDF resources in model.ttl follows certain conventions that relate them to an Ecore metamodel, in the MOF2RDF style:

• There are rdf:type predicates from the RDF resource to another RDF resource whose namespace URI is ePackageNamespaceURI, and local name is eClassName.
• Statements use predicates whose namespace URIs are ePackageNamespaceURI and local names are eStructuralFeatureName:
  • Predicate objects can be other RDF resources (in the case of EReferences), or literals (in the case of EAttributes).
  • RDF lists are supported for many-valued features.

In that case, you could write an .rdfres file like this, and load it as an EMF resource where the relevant RDF resources would be deserialised into EMF EObjects:

dataModels:
  - model.ttl
schemaModels:
  - schema.ttl

The .rdfres file can then be loaded and used by any EMF-compatible tool as usual. Note that the elements in dataModels and schemaModels can be arbitrary URIs understood by the RIOT system in Jena, and not just relative paths from the folder of the .rdfres file.

Model validation

RDF model validation can be enabled by adding a line in the .rdfres, e.g. validationMode: jena-clean. The following validation modes are available :

• none
• jena-valid: validation passes if the model has no internal inconsistencies, even though there may be some warnings.
• jena-clean: validation passes if the model has no internal inconsistencies and there are no warnings.

validationMode: jena-clean
dataModels:
  - model.ttl
schemaModels:
  - schema.ttl

Multi-value attributes

EAttributes with cardinality > 1 ("multi-value attributes") are supported by the resource. This includes support for the unique and ordered flags.

Note that unique values are not enforced by RDF: the resource leaves it to EMF ELists to ensure uniqueness of values. Duplicates in an RDF data model are persisted when handled as an EMF model. Removing a value from a unique where there are duplicates of a value will remove all instances of the duplicate value: this maintains an equivalence between EMF and RDF represenations of the model.

The resource represents multi-value attributes in RDF using Containers or Lists. The resource will opt to update the RDF representation of a multi-value attribute based on its current data structure (container/list) in the RDF data model. However, when there is no existing structure, by default a container will be used. If you would prefer to use lists for representing multi-value attributes, you can specify multiValueAttributeMode: List in the .rdfres file, as follows:

validationMode: jena-clean
dataModels:
  - model.ttl
schemaModels:
  - schema.ttl
multiValueAttributeMode: List

Default model namespace

A default model namespace URI is required when adding new resources to an RDF model. The namespace URI can be configured in the .rdfres file as shown below.

defaultModelNamespace: http://foo/bar/example#

The URI must be absolute, e.g. by starting with file:// (/ will become file) or http://. If you provide an invalid URI, then Jena will revert to using the URI of the named model it loaded the RDF from as the name space.

The example above results in new RDF node with an IRI composed of the default name space and a UUID for the new EObject. E.g. http://foo/bar/example#_6sDDMIgJEfC2g6UdYdL1hg

If a default model namespace is not provided in the .rdfres file, the resource will fall back to the blank prefix PREFIX : <URI> in the RDF model. The last resort is to let Jena decide, which will use the URI that the RDF model was loaded from.

Converting an XMI file to RDF formats

The "Developer Tools for RDF binding for EMF" feature includes converters from XMI to the Turtle and N-Triples serialisation formats for RDF.

To use them, right-click on a file with the .xmi or .model extensions in the Eclipse "Project Explorer" or "Package Explorer" views, and select the appropriate option: