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<img src="http://ericdscott.com/NaturalLexiconLogo.png" alt="NaturalLexicon logo" :width=100 height=100/> ont-app/igraph-grafter

A port of the IGraph protocols to the Grafter protocols (JVM only at present).

Part of the ont-app library, dedicated to Ontology-driven development.

Contents

• Motivation
• Usage
• Keyword Identifiers as URIs
• Literals
  • xsd values
  • #inst values
  • language-tagged-strings
  • Transit-encoding of Clojure containers
• License

<a name="h2-motivation"></a>

Motivation

The people at Swirrl have graciously provided a large body of rdf-centric clojure code on github, largely centered around a project called Grafter. Grafter is largely a wrapper around the API for Eclipse rdf4j, which provides a wide variety of ways to deal with RDF data.

The purpose of this library is to allow connections to grafter-based RDF model to be viewed under the IGraph protocols, which defines a generic container type for named relations between named entities:

(g) -> {s {p #{o}}}
(g s) -> {p #{o}}
(g s p) -> #{o}
(g s p o) -> (truthy)

This also includes a facility to map between namespaced Clojure keywords and URIs.

<a name="h2-usage"></a>

Usage

Available at clojars:

The following code will instantiate a graph:

(ns my-namespace
  {
    :vann/preferredNamespacePrefix "myns"
    :vann/preferredNamespaceUri "http://my.uri.com/"
  }
  (require 
    [grafter-2.rdf4j.repository :as repo]
    [ont-app.igraph-grafter.core :as igraph-grafter]
    [ont-app.vocabulary.core :as voc]  
    ))

(def repo (repo/sail-repo))
(def conn (repo/->connection repo))
(def g (igraph-grafter/make-graph conn :myns/MyGraph))

The repo can be any rdf4j SAIL (Storage And Inference Layer) instantiated by the grafter repository module.

The default is an in-memory store.

Use make-graph to create a wrapper around the connection to allow for IGraph member access methods. Mutability is mutable, meaning that triples are added and removed with add! and subtract!.

> (add! g [:myns/Subject :rdf/type :myns/Thing])
> (g :myns/Subject)
{:rdf/type #{myns/Thing}}
>

See ont-app/IGraph for full documentation of the IGraph and IGraphMutable protocols.

The original connection can be attained with (:conn g). The KWI of the associated named graph can be attained with (:graph-kwi g). This will give you low-level access to the data set. See the Grafter project for details.

<a name="h2-keyword-identifiers"></a>

Keyword Identifiers as URIs

In keeping with the overall approach of the ont-app libraries, URIs are encoded in clojure as Keyword Identifiers (KWIs), using the constructs defined in ont-app/vocabulary.

This library uses metadata attached to Clojure namespaces to define mappings between namespaced keywords in Clojure code and corresponding RDF namespaces.

So in the example above, :myns/Thing would translate to "http://my.uri.com/Thing", because of the vann:preferredNamespacePrefix and vann/preferredNamespaceUri declarations in the metadata of my-namespace.

Blank nodes are interned in the namespace _.

> (bnode-kwi #object[grafter_2.rdf.protocols.BNode yadda "tablegroupG__21835"]
:_/tablegroupG__21835
>

<a name="h2-literals"></a>

Literals

This library is supported by igraph/rdf, which defines a render-literal multimethod. There are methods for each of the types of literals described below.

<a name="h3-xsd"></a>

xsd values

Grafter has its own logic for dealing with xsd datatypes for scalars, and ont-app/igraph-grafter integrates with this directly.

<a name="h3-inst-values"></a>

#inst values

Clojure's #inst reader macro is also supported. Its contents are rendered as a string matching igraph-grafter/date-time-regex, matching the standard format expected by clojure.instant/read-instant-date. For example, #inst "2000" is translated as "2000-01-01T00:00:00Z". Such strings will be matched and instantiated as #inst expressions.

<a name="h3-language-tagged-strings"></a>

language-tagged strings

A #lstr reader macro is defined to support language-tagged strings in clojue code, For example, #lstr "gaol@en-GB" in clojure code will translate to RDF "gaol"@en-GB. Conversely, data imported into a graph from RDF will be translated using the same reader macro.

<a name="h3-transit-encoding"></a>

Transit-encoding of clojure containers

Clojure's standard container classes when provided as literal RDF objects are encoded in RDF as transit, and decoded transparently.

So for example the vector [1 2 3] would be encoded in the RDF store as "[1,2,3]"^^transit:json. When read back in again, it will be reconsituted as the original vector.

This works because clojure's vector type has a clojure derive statement to the dispatch value :rdf-app/TransitData, whose render-literal method does the rendering.

(derive clojure.lang.PersistentVector :rdf-app/TransitData)

If you prefer that a vector or some other clojure composite data structure be handled some other way, this declaration can be reversed with the underive function.

See the documentation of ont-app/rdf for more details.

<a name="h2-license"></a>

License

Copyright © 2020 FIXME

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.