Description: Structured data is sheet-music for search engines.
Also known as structured data, the Semantic Web is centered around the Wikipedia project and Google's Freebase (2007-2016). Semantic Web markup languages have been developed to assist machine learning.
Instead of manual data-entry, datum is collected from "decorated" web-content (mark-up), stategically encoded with name / value pairs. I like to use the word "decorated" because the scripting is similar to making a word or phrase bold in a document. The rules for semantic parent and child nesting of name / value pairs is somewhat complicated and is an art called Library science .
An early example that many may be familiar with is the Virtual Business Card (vCard) , which encodes contact information into a structured format. The Wikipedia uses a closed system called WikiData (2012). Google's Knowledge Graph (2012), and Facebook's Open Graph (2010), are substantially more open than Wikipedia.