Extensible Markup Language (XML)

Introduction
The eXtensible Markup Language (XML) is a formatting language that allow the creation of text documents which are both computer- and human-interpretable. The standards for XML documents are created and maintained by the World Wide Web Consortium (W3C) [1], and describe the rules for marking data with tags. Similar to HTML, the use of tags allows the document creator to place additional meaning around data (whether numeric or text). In the case of XML, the tags are not pre-defined, so the document creator is free to select tag names that describe what the tag contains.

As an example, we will look at a simple XML document that shows a patient with some basic demographics:

  <Patient>
     <ID>1234567</ID>
     <Name>
        <Prefix>Mrs</Prefix>
        <First>Jane</First>
        <Last>Doe</Last>
        <Suffix/>
     </Name>
     <DOB>1/10/1970</DOB>
     <Gender>Female</Gender>
  </Patient>

In the above example, <Patient> is a tag. You will notice that almost all of the tags come in pairs (i.e. <ID> </ID>), with the exception of <Suffix />. Because there is no suffix data, this tag is empty. Empty tags can be displayed as <Suffix></Suffix> or <Suffix />. You will also notice that the tag names used are very descriptive of the data contained within, instead of providing information on how to format the text on the page (like HTML). This is because XML is meant to separate data from display, allowing it to be used instead as a flexible format for transporting information, as opposed to a static view of some data.

XML in Clinical Information Systems
XML can be a very useful method for the storage of medical information. While more traditional relational database management systems (RDBMSs) are used to store discrete data elements, it's possible to use XML documents or XML databases instead. Not only does this allow structuring medical data as you might in a RDBMS, it provides additional flexibility for extending the document and adding new types of data.

In addition to storage, XML is able to facilitate the exchange of medical information over proprietary binary formats, or other formats that are more rigid (such as HL7 v2)

There are several different standards in healthcare for the storage and exchange of clinical documents, such as the HL7 Clinical Document Architecture (CDA) and the ASTM Continuity of Care Record (CCR).

(Article in progress)

1. W3C XML [1]
2. HL7 v3 Messaging Standards [2]
3. Clinical Document Architecture (CDA) [3]
4. Continuity of Care Record (CCR) [4]
5. XML databases [5]

Submitted by Luke Rasmussen