text: 1. An RDF vocabulary for defining data constraints on RDF graphs (which includes OWL since an 
  
  OWL ontology is an RDF graph). 
  
  2. A reasoner for applying the constraints defined in 1 to a specified data graph such as the Pizza 
  
  ontology. 
  
  One of the most important classes in 1 is a SHACL Shape. An instance of the SHACL Shape class 
  consists of a set of Targets and Constraints. A Target defines which nodes in the RDF graph that the data 
  constraints apply to. For OWL ontologies this is typically the name of a class which indicates that the 
  constraints apply to all instances of that class. The Constraints define the specific property for the 
  constraint as well as the actual constraints such as the minimum or maximum number of values and the 
  datatype. In the following example, a Target is the Employee class in the Pizza ontology. An example 
  constraint is that the ssn property must have exactly one value. Another example constraint is that the 
  format of the ssn value must be a string of the form: “NNN-NN-NNNN” where each N must be an 
  integer. For more on SHACL see the references in the bibliography. 
  
  11.4 The Protégé SHACL Plug-In 
  To start go to Windows>Tabs and see if you have SHACL Editor as an option. If you don’t then go to 
  File>Check for plugins and select the SHACL4Protege Constraint Validator. You need to restart Protégé 
  to see the new plugin so save your work and then quit and start Protégé and load the Pizza ontology with 
  data. 