Step 5: Convert the data

Convert the data to RDF

Once you have a schema that you are satisfied with, the next step is to convert the source data into a Linked Data representation or serialization. In this step the data is converted to RDF triples and while applying the naming scheme defined in Step 4. The Resource Description Framework (RDF) is used as a general method for conceptual description or modeling of information that is implemented in web resources, using a variety of syntax notations and data serialization formats. It is similar to classic conceptual modeling approaches such as entity–relationship or class diagrams, as it is based upon the idea of making statements about resources (in particular web resources) in the form of subject-predicate-object expressions. These expressions are known as triples in RDF terminology. The subject denotes the resource, and the predicate denotes traits or aspects of the resource and expresses a relationship between the subject and the object. RDF triples may be stored in a type of database called a triplestore.

Before converting your data to RDF you need to decide how you want to publish the data. Do you want to publish the data as a webservice that can be queried? Following, you need to make sure that your data is in the right format. We advise that you do not chose one single serialization but multiple. Potential serializations for RDF are turtle (human readable), RDF/XML, N3, RDFa (in HTML), and the lately becoming very popular JSON-LD (for JavaScript Developers).

You might decide to first make your data online available via a webservice (API) so developers can easily access your data and test its usability. This can provide you with valuable feedback about the potential value of your data before you engage in the investment to convert your data to RDF.

Conversion approaches fall into three categories:

  • Automatic conversion, sometimes called triplication
  • Partial scripted conversion
  • Modeling by human and subject matter experts, followed by scripted conversion

There are different tools that can be used to do this conversion:

The Simile project made an attempt in proving a directory of tools for converting various data formats into RDF. A similar list can be found by W3C. A tutorial on converting relational data into RDF format is provided by Oracle. For an easy approach to transform spreadsheets to rdf, have a look at one of the books published by the PiLOD project containing a step by step approach based on the Open Refine tool, including screenshots of the tool. If you are interested in expressing customized mappings from relational databases to RDF datasets you should check out the R2RML language.

Once you have converted your data to RDF the next step is to make sure that you have some governance structure in place to maintain and manage your data.

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