Writing in the Sand Other Notations in Digital Libraries

Just a brief introduction here, for:

MathML is an application of XML (Extensible Markup Language) to make it possible to render mathematical expressions in browsers, using appropriate stylesheets. It is also a low-level specification for describing mathematics for machine to machine communication. A working group has been formed to develop version 3.0, but version 2.0 has been out since 2001, and may be supported in your browser with the addition of plugins and/or fonts. A test page is available here.

Some of the elements used for display are listed here with their meanings, for reference in the example which follows:

Presentation Markup:

Content markup:

All of this is from the Version 2.0 specifications. Here's a sample of how it looks, for the notation:

\displaystyle \int_1^t \frac{\diffd x}{x}
    Markup:


	<mrow>
	<semantics>
	  <mrow>
	    <msubsup>
	      <mo>&int;</mo>
	      <mn>1</mn>
	      <mi>t</mi>
	    </msubsup>
	    <mfrac>
	      <mrow>
	        <mo>&dd;</mo>
	        <mi>x</mi>
	      </mrow>
	      <mi>x</mi>
	    </mfrac>
	  </mrow>
	  <annotation-xml encoding="MathML-Content">
	    <apply>
	      <int/>
	      <bvar><ci>x</ci></bvar>
	      <lowlimit><cn>1</cn></lowlimit>
	      <uplimit><ci>t</ci></uplimit>
	      <apply>
	        <divide/>
	        <cn>1</cn>
	        <ci>x</ci>
	      </apply>
	    </apply>
	  </annotation-xml>
	</semantics>
	</mrow>
             
            

"In this example, we use the semantics element to provide a MathML content expression to serve as a "semantic annotation" for a presentation expression. In the display markup, we have used the msubsup element to attach a subscript and a superscript to an expression, in this case the integral sign. We also used entities &int; and &dd; to specify the integral and differential symbols."

"The semantics element has as its first child the expression being annotated, and the subsequent children are the annotations. There is no restriction on the kind of annotation that can be attached using the semantics element. For example, one might give a TEX encoding, or computer algebra input in an annotation. The type of annotation is specified by the encoding attribute and the annotation and annotation-xml elements."




Resource Description Framework (RDF) is a simple notation for representing relationships between and among objects (or concepts). It is particularly intended for representing metadata about Web resources, and is intended for situations in which this information needs to be processed by applications, rather than being only displayed to people. RDF provides a common framework for expressing this information so it can be exchanged between applications without loss of meaning.

RDF identifies things using Web identifiers (called Uniform Resource Identifiers, or URIs), and describing resources in terms of simple properties and property values. This enables RDF to represent simple statements about resources as a graph of nodes and arcs representing the resources, and their properties and values.

In the following example, the group of statements "there is a Contact Person identified by http://www.w3.org/People/EM/contact#me, whose name is Eric Miller, whose email address is em@w3.org, and whose title is Dr." could be represented as this RDF graph.

From the W3C RDF Primer:

graph of Eric Miller relationships in RDF


      <?xml version="1.0"?>
      <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
             xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#">
        <contact:Person rdf:about="http://www.w3.org/People/EM/contact#me">
	    <contact:fullName>Eric Miller</contact:fullName>
	    <contact:mailbox rdf:resource="mailto:em@w3.org"/>
	    <contact:personalTitle>Dr.</contact:personalTitle> 
        </contact:Person>
      </rdf:RDF>
            
           

RDF is based on the idea that the things being described have properties which have values, and that resources can be described by making statements that specify those properties and values. RDF uses a particular terminology for talking about the various parts of statements. Specifically, the part that identifies the thing the statement is about (the contact person) is called the subject. The part that identifies the property or characteristic of the subject that the statement specifies (full name, mailbox, title) is called the predicate, and the part that identifies the value of that property (Eric Miller, mailto: address, "Dr.") is called the object.

There are three RDF vocabularies under active development, all for Simple Knowledge Organization System (SKOS):

  1. SKOS Core,
  2. SKOS Mapping, and
  3. SKOS Extensions.

Some examples of how RDF might be used to make digital libraries more functional and interoperable are outlined in "What is a Digital Library Anymore, Anyway? Beyond Search and Access in the NSDL", by Carl Lagoze, Dean Krafft, Sandy Payette, Susan Jesuroga in DLib Magazine, (November 2005) 11:11, and "An Interoperable Fabric for Scholarly Value Chains", by Herbert Van de Sompel, Carl Lagoze, Jeroen Bekaert, Xiaoming Liu, Sandy Payette, and Simeon Warner, in DLib Magazine (October 2006), 12:10.

Girl writing in the sand

This information is provided without guarantees as to validity or completeness, particularly in light of the fact that the world of metadata in digital libraries is a world of shifting sands, constantly changing.