Tutorial: Ontology Development

"What's up folks." Today we are going to create a movie database ontology for a client of your Acme company.

Step 1: Setup Ontology Plug-in

Ontologies are encapsulated in OSGi bundles. In eclipse we develop them as equinox plug-ins. An ontology bundle is a package that contains the sources (graph/*.pgraph), a compiled graph file (graph.tg), and Java resource files (src/ and bin/).

Open a New Plug-in Project wizard:

• Open Plug-in Development Perspective
• Select File >> New >> Other
• Select Plug-in Development >> Plug-in Project

A New Plug-in Project wizard will open.

• Our organization is Acme Software ltd and from there is our plug-in name derived, com.acme.movie.ontology. Insert that as project name. Next >
• In the following page you should know that this plugin does not contribute to UI, does not need an activator and is not a rich client application. Next >
• Use template Plug-in with a Simantics Ontology. Next >
• Your company domain is com.acme.movie and ontology name Movie, and the inital version is 1.0. Finish

You have now a new project in Package Explorer. In it you will find META-INF/MANIFEST.MF, graph/Movie.pgraph, and graph.tg.

Step 2: Initialize Ontology

Open Movie.pgraph and start editing.

As you are using Layer0 concepts, it is a good idea to capture its namespace:

 L0 = <http://www.simantics.org/Layer0-1.0>

Your acme company has a namespace. You are creating a new one so it must be stated.

 <http://com.acme> : L0.Library
     @L0.new

The ontology has a representing resource, an instance of L0.Ontology. Don't forget to tell the compiler to create Resource file aswell.

 Movie = <http://com.acme/Movie-1.0> : L0.Ontology
     L0.HasResourceClass "com.acme.ontology.Movie"

Step 3: Export package

Now that you have some content, graph compiler has created a Resource class com.acme.ontology.Movie under src/ folder. When developing database code you can gain access to your ontology concepts using this class. In OSGi plugin environment, the access to other plugins' classes is denied by default. To share, you must export its Java package.

• Open META-INF/MANIFEST.MF
• Add Exported Packages >> com.acme.ontology

Your MANIFEST.MF should look like this.

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Ontology
Bundle-SymbolicName: com.acme.movie.ontology
Bundle-Version: 1.0.0.qualifier
Bundle-Vendor: Acme Software ltd
Bundle-RequiredExecutionEnvironment: JavaSE-1.6
Require-Bundle: org.simantics.layer0;bundle-version="1.0.0"
Export-Package: com.acme.ontology

Step 4: Write your Movie Ontology

In movie database we are going to store objects such as movies, actors, directors and producers. There is going to be a few properties about them, and a couple of relations. At this point it is a good idea to take a look at the graph file format documentation. Open Movie.pgraph again.

• Specify Types

First we need to specify object types for the concepts Movie, Role and Person. Actors, directors and producers are modelled as Persons. A person becomes a representative of a classification, say actor, once he/she has acted in a motion picture (there is a relation).

// Types
Movie.Movie <T L0.Entity
Movie.Role <T L0.Entity
Movie.Person <T L0.Entity

• Specify Properties

// Properties
Movie.HasDobYear <R L0.HasProperty
    L0.HasRange L0.Integer  
Movie.HasAge <R L0.HasProperty
    L0.HasRange L0.Double  
Movie.HasGender <R L0.HasProperty
    L0.HasRange Movie.Gender

• Specify Literals

Gender is a special case, since it is not defined in Layer0 you must define yourself. The syntax is defined in Datatype documentation. In it you will find out the format for your enumeration is |Male|Female.

// Literals
Movie.Gender <T L0.Literal
    @L0.assert L0.HasDataType $(|Male|Female)

• Add the properties to your types

Add properties with @L0.singleProperty or @L0.optionalProperty. They are actually restrictions. The former means that an instance of Role is a valid instance only it has a single HasAge relation to an integer literal.

Movie.Role
    @L0.singleProperty Movie.HasAge
    @L0.singleProperty Movie.HasGender
Movie.Person
    @L0.singleProperty Movie.HasDobYear
    @L0.singleProperty Movie.HasGender

• Specify Relations

// Relations
Movie.IsDirectedBy <R L0.IsRelatedTo
    L0.HasDomain Movie.Movie
    L0.HasRange Movie.Person
Movie.IsDirectorOf <R L0.IsRelatedTo
    L0.InverseOf Movie.IsDirectedBy
    L0.HasDomain Movie.Person
    L0.HasRange Movie.Movie

Movie.IsWrittenBy <R L0.IsRelatedTo
    L0.HasDomain Movie.Movie
    L0.HasRange Movie.Person
Movie.HasWritten <R L0.IsRelatedTo
    L0.InverseOf Movie.IsWrittenBy
    L0.HasDomain Movie.Person
    L0.HasRange Movie.Movie

Movie.IsProducedBy <R L0.IsRelatedTo
    L0.HasDomain Movie.Movie
    L0.HasRange Movie.Person
Movie.IsProducerOf <R L0.IsRelatedTo
    L0.InverseOf Movie.IsProducedBy
    L0.HasDomain Movie.Movie
    L0.HasRange Movie.Person

Movie.Played <R L0.IsRelatedTo
    L0.HasDomain Movie.Person
    L0.HasRange Movie.Role
Movie.IsPlayedBy <R L0.IsRelatedTo
    L0.InverseOf Movie.Played
    L0.HasDomain Movie.Role
    L0.HasRange Movie.Person

Save file. Your Movie.java resource file should now contain a list of resources and URIs. Go ahead and take a look.

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Congratulations You have now set-up an ontology.

Give your brains a break before proceeding to the next tutorial.
Tutorial 3: Feature Development