This chapter proposes exercises to manipulate and query real-world RDFS ontologies, and especially Yago. Yago was developed at the Max Planck Institute in Saarbrücken in Germany. At the time of this writing, it is the largest ontology of human quality that is freely available. It contains millions of entities such as scientists, and millions of facts about these entities such as where a particular scientist was born. Yago also includes knowledge about the classes and relationships composing it (e.g., a hierarchy of classes and relationships).

EXPLORING AND INSTALLING YAGO

Go to the Yago Web site, http://mpii.de/yago, click on the Demo tab and start the textual browser. This browser allows navigating through the Yago ontology.

1. Type “Elvis Presley” in the box. Then click on the Elvis Presley link. You will see all properties of Elvis Presley, including his biographic data and his discography.

2. You can follow other links to explore the ontology. Navigate to the wife of Elvis Presley, Priscilla.

3. The ontology is held together by a taxonomy of classes. Its top class is called “entity”. Verify this by repeatedly following type and sub Class Of links.

4. Go back to Elvis Presley. Navigate to one of his songs. You will see the date the song was recorded. Can you find all songs together with their record dates? Why would this be a tedious endeavor?

Then, to install Yago on your machine, make sure that you have Java installed and around 5 GB free disk space.