text: Next, we will look at a plugin for SHACL. SHACL stands for Shapes Constraint Language. Note that 
  *shape*in this context has nothing to do with geometric shapes. SHACL is somewhat newer than the other 
  technologies described here. However, it fills an essential gap in the Semantic Web architecture stack, and 
  it is gaining a lot of traction in the world of large-scale corporate development. The reason for SHACL 
  may at first seem a bit hard to grasp. After all many of the constraints that SHACL can define for data can 
  also be defined using Description Logic or SWRL which are more high level and a bit easier to use. So 
  why even bother with SHACL? There are two reasons that SHACL is essential for real world use of 
  Semantic Web and Knowledge Graph technology: 
  
  1. The need to define constraints that aren’t limited by the Open World Assumption (OWA) and 
  
  Monotonic reasoning. 
  
  2. The fact that real world data is*messy!*
  
  11.1 OWA and Monotonic Reasoning 
  As described in section 4.13 OWL uses the Open World Assumption (OWA) because it was designed for 
  the Internet. However, the OWA makes certain kinds of constraint validation difficult or impossible. For 
  example, it is common to have a data integrity constraint that all employees must have a social security 
  number. While such an axiom can be defined in OWL it will seldom work when we want it to because of 
  the OWA. The OWA means that there may be a social security number out there somewhere in the 
  Internet but that the system just hasn’t found it yet. While this is true, to validate the integrity of corporate 
  data just saying “well it is out there somewhere” won’t do. To validate data integrity we need to be able to 
  fire off warnings when required data isn’t there so we need to use the Closed World Assumption (CWA). 