I am now into Unit 3 of my current MOOC undertaking, “Metadata: Organizing and Describing Information.” This week requires students to roll up their sleeves a bit and delve into a bit of the behind-the-scenes aspect of metadata.
There are many different metadata schemas out there; some of the more familiar ones include the Dublin Core, VRA, and MODS. However, we learned in this unit that metadata schemas can be built from scratch by anyone, but in order for them to function properly within the what is known as the Semantic Web, they must be built upon three technologies: XML, DTD, and RDF.
XML stands for Extensible Markup Language, and is a mark-up language that defines values for how to create structured documents. It is made up of elements and values and can have attributes which, in turn, also have values. XML is made up of parent-child relationships, so the “children” inherit the values and attributes of their “parents.”
DTD stands for Document Type Declaration, and is a “declaration” which defines the elements of an XML document. The DTD is made in the header of the coding for a Web page. Withing the DTD itself there is most often an address which points to another document residing somewhere on the Internet. This document contains a set of markup declarations that define a document type for a markup language, such as XML.
RDF stands for Resource Description Framework and is not really a technology, but rather a model of how to declare elements. It’s an infrastructure that enables the exchange of structured metadata and is key to the success of the Semantic Web.