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.
All types can be expected to have a name (L0.HasName) and therefore does not need explicit statement.
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.
Congratulations You have now set-up an ontology.
Give your brains a break before proceeding to the next tutorial.
Tutorial 3: Feature Development