ST 2005 Note #3 - The Semantic Tech Stack

The semantic web has a technological stack that looks like this (from a W3C perspective):

+---------------------------------+
+                XML              +
+---------------------------------+
+                RDF              +          
+---------------------------------+
+            RDF-Schema           +
+---------------------------------+
+  Ontology Vocabulary (e.g. OWL) +
+---------------------------------+
+              Logic              +
+---------------------------------+

RDF and RDF Schema have been covered in brief in earlier notes. OWL is based heavily on work done as part of DAML+OIL. The aim of DAML was to provide the ability to infer facts from an instance document and its associated ontological schema. OWLs aim appears to be very similar. As we move up the stack we find increasing capabilities in a number of areas:

1. Ability to define types, relationships and constraints (i.e. structural constraints).
   
2. Ability to infer facts not explicitly represented in an instance document.
   
3. Ability to define semantic constraints, business rules in other words[1].
   

This comes at a price; ontology production[2], validation costs rise and inference engine sophistication rises.

---

[1] Not sure this is different from 1) in any meaningful way but it feels different.
[2] As more sophisticated ontologies are modeled using complex logic assertions then more analysis and design time is required for each ontology.