Storage and Access Fundamentals

The most basic way to store and access ontological information is by using regular XML files written using RDF and OWL syntax. These files can be stored on a computer that you access locally or they can be made accessible to others by hosting them on a public Web server. OWL files are commonly used and can be opened and saved by editing programs such as Protege and TopBraid.

Ontologies are often stored online, either on a Web server, repository, or possibly by programatic means. These ontologies become available via a URL and, when used with repositories, can include advanced features like versioning and URI generation. MMI provides more information about registering and accessing ontologies for those interested in an ontology providers perspective.

Triple Stores

Another common method for storing ontologies involves the use of a database-like technology called a triple store. RDF documents can be expressed in these stores in their triple state, meaning that the information is stored as statements including subject, predicate, and object. There is a lot of debate about just how effective triple-stores are, especially in relation to traditional database technologies, and it remains to be seen exactly how they will emerge as the technology matures.

Triple stores are optimized for handling the type of RDF data that make up ontologies and can be queried to discover information about data and its relationships. SPARQL is a query language, similar to SQL, that can be used to write queries specific to RDF data, meaning that you can query using semantic data provided in the ontologies you are working with.

SPARQL

SPARQL is an emerging standard method for making queries about RDF triples against RDF data stores. Unlike SQL, SPARQL is RDF-aware, meaning that it can take advantage of the definitions and descriptions provided in ontologies.

For example, you could limit your search to "all things that are the color red" or "all documents created by President Lincoln and anyone who worked with President Lincoln." Of course, the ontologies and datasets you are querying will need to be properly described and defined for this to work.

SPARQL has the capabilities to support many more complex queries than the simple examples above. SPARQL contains specific provisions for use in obtaining descriptions about particular RDF resources. The query language also supports advanced methods for filtering results, including the use of regular expressions.

Suggested Citation

Alexander, P. 2011. "Storage and Access Fundamentals." In The MMI Guides: Navigating the World of Marine Metadata. http://marinemetadata.org/guides/vocabs/ont/coretech/storage. Accessed December 6, 2019.