This document provides an overview of ontologies and linked open data, including some real-world applications. It discusses how ontologies add semantics to data storage and querying by defining types of entities and their relationships. Popular ontologies like DCTerms and FOAF are mentioned. Examples of linked open data in the Facebook API and DBpedia are provided. The differences between relational and graph databases are outlined. SPARQL is introduced as the query language for graph databases, and Virtuoso is presented as an example of a non-relational, graph database.