PluginAnatomy
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Contents
Introduction
The purpose of this web page is to describe some of the key ingredients of a plugin. The page will be directed by the quick development of a plugin and can indeed be used as a quick start guide. However, we will assume that the reader has an understanding of Java development and knows how to follow along in his favorite IDE. For more information about how to work with protege 4 in an IDE I will direct the reader to this page.
The vacuous plugin in one minute
Before we can start, we must set the PROTEGE_HOME environment variable to point to a Protege 4 distribution. This page has directions on how to do this in different operating systems but for now I will assume that we are on a unix (or os x) system. In that case, the system variable can be set with a simple commandexport PROTEGE_HOME=/Users/tredmond/Desktop/Protege_4.0_betaThe simplest (trivial) plugin can be built from sources in the following layout:
build.xml META-INF MANIFEST.MF lib resources srcAs we will see - even without any java sources - this is a sufficient basis for building a plugin that is recognized by Protege 4. There are only two files in this source tree - the build.xml file and the MANIFEST.MF. These files can be quickly put together from templates.
Build.xml
The template for the build.xml file can be downloaded from here. Only two things need to be changed in this build file. They can be found by searching for the string "CHANGE ME" in the file. The first thing to change is the name of the project. I will call the project the plugin tutoiral project:<project name = "plugin tutorial" default = "install" basedir = ".">The next setting that must almost always be changed is the name of the plugin. In this case, the build.xml already has the right name for the plugin but this is the only plugin for which this will be true:
<property name = "plugin" value = "org.protege.owl.examples.tab"/>
With these adjustments the build.xml file is ready.
MANIFEST.MF
The template for the MANIFEST.MF file can be downloaded from here. Only five things need to be changed in this file to make it useable and two are optional. These can be found by searching for the string "CHANGE ME" in the file. The first change is to set the display name for the plugin:Bundle-Name: Tutorial PluginThis is the name that is seen when Protege 4 starts up and in several plugin configuration screens. The seccond thing to change is the symbolic name of the plugin. The usual default is to uses the same name as the plugin name in the build.xml file:
Bundle-SymbolicName: org.protege.editor.owl.example.tab;singleton:=trueNote the "singleton:=true" line - this is important since most Protege 4 plugins will only work if they are instantiated exactly once. The next things to change are the bundle description, the vendor and the documentation url:
Bundle-Description: A simple plugin for a plugin development tutorial Bundle-Vendor: The Protege Development Team Bundle-DocURL: www.perhaps.i.donthaveoneyet.com
Actually the vendor and the docurl are optional and can be deleted. The MANIFEST.MF file is now ready.
Compile and Run
This vacuous plugin is now ready to compile and run. Assuming that the PROTEGE_HOME environment variable is set correctly, this plugin can be compiled with the simple commandant installThe full text of the build session is as follows:
[tredmond@Andromeda org.protege.editor.owl.examples.tab]$ ant install Buildfile: build.xml init: [mkdir] Created dir: /private/tmp/org.protege.editor.owl.examples.tab/build [mkdir] Created dir: /private/tmp/org.protege.editor.owl.examples.tab/build/classes [mkdir] Created dir: /private/tmp/org.protege.editor.owl.examples.tab/build/classes/lib [mkdir] Created dir: /private/tmp/org.protege.editor.owl.examples.tab/build/lib checkProtegeLibs: [echo] Using Protege Home = /Andromeda/Users/tredmond/dev/workspaces/protege4/owleditor/build/dist/equinox to find protege jars checkProtegeLibsAndReport: buildlibs: [unjar] Expanding: /Andromeda/Users/tredmond/dev/workspaces/protege4/owleditor/build/dist/equinox/bundles/org.protege.common.jar into /private/tmp/org.protege.editor.owl.examples.tab/build compile: build.manifest: [copy] Copying 1 file to /private/tmp/org.protege.editor.owl.examples.tab/build copy.resources: [mkdir] Created dir: /private/tmp/org.protege.editor.owl.examples.tab/build/classes/META-INF [copy] Copying 1 file to /private/tmp/org.protege.editor.owl.examples.tab/build/classes/META-INF jar: [jar] Building jar: /private/tmp/org.protege.editor.owl.examples.tab/build/org.protege.owl.examples.tab.jar install: [delete] Deleting directory /Andromeda/Users/tredmond/dev/workspaces/protege4/owleditor/build/dist/equinox/configuration/org.eclipse.core.runtime [delete] Deleting directory /Andromeda/Users/tredmond/dev/workspaces/protege4/owleditor/build/dist/equinox/configuration/org.eclipse.osgi [copy] Copying 1 file to /Andromeda/Users/tredmond/dev/workspaces/protege4/owleditor/build/dist/equinox/plugins BUILD SUCCESSFUL Total time: 2 seconds [tredmond@Andromeda org.protege.editor.owl.examples.tab]$If the PROTEGE_HOME environment variable is not set correctly the user will instead see the following:
BUILD FAILED /private/tmp/org.protege.editor.owl.examples.tab/build.xml:74: missing protege libraries
We can now look at what the build has done by exploring the project directory tree. We see the following elements:
- The Class Tree is (approximately) a flattened view of the plugin (the jar file). Generally this largely consists of the .class files that have been compiled from the java. But since we have not written any java yet this is not found. In addition, this will contain resources needed by the plugin and libraries that the plugin needs but which cannot be found in other Protege plugins.
- The Generated Libraries which are extracted from Protege plugins. This is needed because of a difference between how Java and OSGi get resources out of Jar files. OSGi allows a plugin (which is a implemented as a jar file) to contain other jar files. If the bundle classpath is configured correctly, OSGi will load classes from those jars in jars. But Java does not have this capability. So the build script extracts the jar files out of the OSGi plugins that will be needed to compile the plugin.
- The Protege 4 Plugin this is the final artifact of the build process. Because we have run "ant install" it has also been installed in the Protege distribution.
Starting Protege 4 OWL Editor (Version 4.0.111) Platform: Java: JVM 1.5.0_16-b06-284 Memory: 207M Language: en, Country: US Framework: Eclipse (1.4.0) OS: MacOSX (10.5.6) Processor: ppc Installed plugin Pellet Reasoner Installed plugin DL Query Tab Installed plugin Owlviz Plug-in Installed plugin owleditor Installed plugin Tutorial Plugin Installed plugin The OWL API Installed plugin Factplusplus Plug-in Tutorial Plugin Plugin has no plugin.xml resource
In this output we see that the Tutorial Plugin has been recognized and installed. In addition there is a informational message that the plugin.xml file has not been found. This is almost always indicates a problem because most Protege 4 plugins depend on a plugin.xml resource. We will describe how the plugin.xml file is generated in the next sections.
Adding content to the plugin
The previous plugin added precisely no functionality to Protege 4. We are now going to describe how to remedy this situtaion.