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| <h1 class="title">Creating Jena models</h1> |
| |
| |
| <main class="d-flex flex-xl-row flex-column"> |
| |
| <aside class="text-muted align-self-start mb-3 p-0 d-xl-none d-block"> |
| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#introduction">Introduction</a></li> |
| <li><a href="#simple-model-creation">Simple model creation</a></li> |
| <li><a href="#database-model-creation">Database model creation</a></li> |
| <li><a href="#inference-model-creation">Inference model creation</a></li> |
| <li><a href="#ontology-model-creation">Ontology model creation</a></li> |
| <li><a href="#creating-models-from-assembler-descriptions">Creating models from Assembler descriptions</a> |
| <ul> |
| <li><a href="#file-based-models">File-based models</a></li> |
| </ul> |
| </li> |
| <li><a href="#modelmakers">ModelMakers</a></li> |
| <li><a href="#miscellany">Miscellany</a></li> |
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| <article class="flex-column me-lg-4"> |
| <h2 id="introduction">Introduction</h2> |
| <p>Jena is a moderately complicated system, with several |
| different kinds of <code>Model</code> and ways of constructing them. This note |
| describes the Jena <code>ModelFactory</code>, a one-stop shop for |
| creating Jena models. <code>ModelFactory</code> lives in Java package |
| <code>org.apache.jena.rdf.model</code>.</p> |
| <p>This note is an introduction, not an exhaustive description. As |
| usual consult the Javadoc for details of the methods and classes to |
| use.</p> |
| <h2 id="simple-model-creation">Simple model creation</h2> |
| <p>The simplest way to create a model (if not the shortest) is to call |
| <code>ModelFactory.createDefaultModel()</code>. This [by default] delivers a |
| plain RDF model, stored in-memory, that does no inference and has |
| no special ontology interface.</p> |
| <h2 id="database-model-creation">Database model creation</h2> |
| <p>For methods of creating models for <a href="/documentation/tdb/index.html">TDB</a> |
| please see the relevant reference sections.</p> |
| <h2 id="inference-model-creation">Inference model creation</h2> |
| <p>An important feature of Jena is support for different kinds of |
| inference over RDF-based models (used for RDFS and OWL). |
| Inference models are constructed by applying <em>reasoners</em> to |
| <em>base models</em> and optionally <em>schema</em>. The statements deduced by |
| the reasoner from the base model then appear in the inferred model |
| alongside the statements from the base model itself. |
| RDFS reasoning is directly available:</p> |
| <ul> |
| <li> |
| <p><code>createRDFSModel(Model base)</code> creates an inference model over the |
| base model using the built-in RDFS inference rules and any RDFS |
| statements in the base model.</p> |
| </li> |
| <li> |
| <p><code>createRDFSModel(Model schema, Model base)</code> creates an RDFS |
| inference model from the base model and the supplied schema model. |
| The advantage of supplying the schema separately is that the |
| reasoner may be able to compute useful information in advance on |
| the assumption that the schema won’t change, or at least not change |
| as often as the base model.</p> |
| </li> |
| </ul> |
| <p>It’s possible to use other reasoning systems than RDFS. For these a |
| Reasoner is required:</p> |
| <ul> |
| <li> |
| <p><code>createInfModel(Reasoner reasoner, Model base)</code> creates an |
| inference model using the rules of <code>reasoner</code> over the model |
| <code>base</code>.</p> |
| </li> |
| <li> |
| <p><code>createInfModel(Reasoner reasoner, Model schema, Model base)</code> Just |
| as for the RDFS case, the schema may be supplied separately to |
| allow the reasoner to digest them before working on the model.</p> |
| </li> |
| </ul> |
| <p>From where do you fetch your reasoners? From the |
| <em>reasoner registry</em>, the class |
| <a href="/documentation/javadoc/jena/org.apache.jena.core/org/apache/jena/reasoner/ReasonerRegistry.html">ReasonerRegistry</a>. |
| This allows reasoners to be looked up by name, but also provides |
| some predefined access methods for well-know reasoners:</p> |
| <ul> |
| <li> |
| <p><code>getOWLReasoner()</code>: the reasoner used for OWL inference</p> |
| </li> |
| <li> |
| <p><code>getRDFSReasoner()</code>: the reasoner used for RDFS inference</p> |
| </li> |
| <li> |
| <p><code>getTransitiveReasoner()</code>: a reasoner for doing subclass and |
| sub-property closure.</p> |
| </li> |
| </ul> |
| <h2 id="ontology-model-creation">Ontology model creation</h2> |
| <p>An <em>ontology model</em> is one that presents RDF as an ontology - |
| classes, individuals, different kinds of properties, and so forth. |
| Jena supports RDFS and OWL ontologies through <em>profiles</em>. |
| There is extensive documentation on |
| <a href="../ontology/index.html">Jena’s ontology support</a>, so all we’ll do |
| here is summarise the creation methods.</p> |
| <ul> |
| <li> |
| <p><code>createOntologyModel()</code> Creates an ontology model which is |
| in-memory and presents OWL ontologies.</p> |
| </li> |
| <li> |
| <p><code>createOntologyModel(OntModelSpec spec, Model base)</code> Creates an |
| ontology model according the |
| <a href="/documentation/javadoc/jena/org.apache.jena.core/org/apache/jena/ontology/OntModelSpec.html">OntModelSpec</a> |
| <code>spec</code> which presents the ontology of <code>base</code>.</p> |
| </li> |
| <li> |
| <p><code>createOntologyModel(OntModelSpec spec, ModelMaker maker, Model base)</code> |
| Creates an OWL ontology model according to the <code>spec</code> over the |
| <code>base</code> model. If the ontology model needs to construct additional |
| models (for OWL imports), use the <code>ModelMaker</code> to create them. [The |
| previous method will construct a <code>MemModelMaker</code> for this.]</p> |
| </li> |
| </ul> |
| <p>Where do <code>OntModelSpec</code>s come from? There’s a cluster of |
| constants in the class which provide for common uses; to name but |
| three:</p> |
| <ul> |
| <li> |
| <p><code>OntModelSpec.OWL_MEM_RDFS_INF</code> OWL ontologies, model stored in |
| memory, using RDFS entailment only</p> |
| </li> |
| <li> |
| <p><code>OntModelSpec.RDFS_MEM</code> RDFS ontologies, in memory, but doing no |
| additional inferences</p> |
| </li> |
| <li> |
| <p><code>OntModelSpec.OWL_DL_MEM_RULE_INF</code> OWL ontologies, in memory, with |
| the full OWL Lite inference</p> |
| </li> |
| </ul> |
| <h2 id="creating-models-from-assembler-descriptions">Creating models from Assembler descriptions</h2> |
| <p>A model can be built from a description of the required model. |
| This is documented in the |
| <a href="../assembler/assembler-howto.html">assembler howto</a>. |
| Access to the |
| assembler system for model creation is provided by three |
| ModelFactory methods:</p> |
| <ul> |
| <li> |
| <p><code>assembleModelFrom( Model singleRoot )</code>: assemble a Model from the |
| single Model description in <code>singleRoot</code>. If there is no such |
| description, or more than one, an exception is thrown. If a |
| description has to be selected from more than one available |
| candidates, consider using the methods below.</p> |
| </li> |
| <li> |
| <p><code>findAssemblerRoots( Model m )</code>: answer a Set of all the Resources |
| in <code>m</code> which are of type <code>ja:Model</code>, ie descriptions of models to |
| assemble. (Note that this will include sub-descriptions of embedded |
| models if they are present.)</p> |
| </li> |
| <li> |
| <p><code>assembleModelFrom( Resource root )</code>: answer a Model assembled |
| according to the description hanging from <code>root</code>. |
| Assemblers can construct other things as well as models, and the |
| Assembler system is user-extensible: see the howto for details.</p> |
| </li> |
| </ul> |
| <h3 id="file-based-models">File-based models</h3> |
| <p>The method <code>ModelFactory.createFileModelMaker(String)</code> returns a |
| <code>ModelMaker</code> which attaches models to filing-system files. The |
| <code>String</code> argument is the <em>fileBase</em>. When a file-ModelMaker opens a |
| file, it reads it from a file in the directory named by the |
| fileBase; when the model is closed (and <em>only</em> then, in the current |
| implementation), the contents of the model are written back to the |
| file.</p> |
| <p>Because the names of models in a modelMaker can be arbitrary |
| character strings, in particular URIs, they are translated slightly |
| to avoid confusion with significant characters of common filing |
| systems. In the current implementation,</p> |
| <ul> |
| <li>colon : is converted to \_C</li> |
| <li>slash / is converted to \_S</li> |
| <li>underbar _ is converted to \_U</li> |
| </ul> |
| <h2 id="modelmakers">ModelMakers</h2> |
| <p>Plain models can be given names which allows them to be “saved” and |
| looked up by name later. This is handled by implementations of the |
| interface <code>ModelMaker</code>; each <code>ModelMaker</code> produces Models of the |
| same kind. The simplest kind of <code>ModelMaker</code> is a memory model |
| maker, which you get by calling |
| <code>ModelFactory.createMemModelMaker()</code>. The methods you’d want to use |
| to start with on a ModelMaker are:</p> |
| <ul> |
| <li> |
| <p><code>createModel(String)</code>: create a model with the given name in the |
| ModelMaker. If a model with that name already exists, then that |
| model is used instead.</p> |
| </li> |
| <li> |
| <p><code>openModel(String)</code>: open an existing model with the given name. If |
| no such model exists, create a new empty one and give it that name. |
| [createModel(String) and openModel(String) behave in the same way, |
| but each has a two-argument form for which the behaviour is |
| different. Use whichever one best fits your intention.]</p> |
| </li> |
| <li> |
| <p><code>createModel()</code>: create a fresh anonymous model.</p> |
| </li> |
| <li> |
| <p><code>getModel()</code>: each <code>ModelMaker</code> has a <em>default model</em>; this method |
| returns that model.</p> |
| </li> |
| </ul> |
| <p>There are other methods, for removing models, additional control |
| over create <em>vs</em> open, closing the maker, and looking names up; for |
| those consult the |
| <a href="/documentation/javadoc/jena/org.apache.jena.core/org/apache/jena/rdf/model/ModelMaker.html">ModelMaker JavaDoc</a>.</p> |
| <h2 id="miscellany">Miscellany</h2> |
| <p>Finally, <code>ModelFactory</code> contains a collection of methods for some |
| special cases not conveniently dealt with elsewhere.</p> |
| <p><code>createModelForGraph(Graph g)</code> is used when an advanced user with |
| access to the Jena SPI has constructed or obtained a <code>Graph</code> and |
| wishes to present it as a model. This method wraps the graph up as |
| a plain model. Alterations to the graph are visible in the model, |
| and <em>vice versa</em>.</p> |
| |
| </article> |
| |
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| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#introduction">Introduction</a></li> |
| <li><a href="#simple-model-creation">Simple model creation</a></li> |
| <li><a href="#database-model-creation">Database model creation</a></li> |
| <li><a href="#inference-model-creation">Inference model creation</a></li> |
| <li><a href="#ontology-model-creation">Ontology model creation</a></li> |
| <li><a href="#creating-models-from-assembler-descriptions">Creating models from Assembler descriptions</a> |
| <ul> |
| <li><a href="#file-based-models">File-based models</a></li> |
| </ul> |
| </li> |
| <li><a href="#modelmakers">ModelMakers</a></li> |
| <li><a href="#miscellany">Miscellany</a></li> |
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| <script src="/js/popper.min.js.js" type="text/javascript"></script> |
| <script src="/js/bootstrap.min.js" type="text/javascript"></script> |
| <script src="/js/improve.js" type="text/javascript"></script> |
| |
| <script type="text/javascript"> |
| (function() { |
| 'use strict' |
| |
| |
| |
| const links = document.querySelectorAll(`a[href="${window.location.pathname}"]`) |
| if (links !== undefined && links !== null) { |
| for (const link of links) { |
| |
| link.classList.add('active') |
| let parentElement = link.parentElement |
| let count = 0 |
| const levelsLimit = 4 |
| |
| |
| |
| |
| |
| while (['UL', 'LI'].includes(parentElement.tagName) && count <= levelsLimit) { |
| if (parentElement.tagName === 'LI') { |
| |
| |
| |
| parentElement.querySelector('a:first-child').classList.add('active') |
| } |
| parentElement = parentElement.parentElement |
| count++ |
| } |
| } |
| } |
| })() |
| </script> |
| |
| </body> |
| </html> |
