Difference between revisions of "Extensible Markup Language (XML)"

Revision as of 03:05, 27 February 2010

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 some basic demographics for a fictional patient:

  <Patient>
     <ID>1234567</ID>
     <Name>
        <Prefix>Mrs</Prefix>
        <First>Jane</First>
        <Last>Doe</Last>
        <Suffix/>
     </Name>
     <DOB>1/10/1970</DOB>
     <Gender>Female</Gender>
     <PhoneNumbers>
        <Phone type="Home">555-555-5555</Phone>
        <Phone type="Cell">555-555-5556</Phone>
     </PhoneNumbers>
  </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 />. Also, XML allows attributes which can provide some additional information for a tag. In the above example, the Phone tags have an attribute named "type" which describe the type of phone number displayed.

In addition, note that the tag names and attributes used are very descriptive of the data contained within, unlike HTML where tags only provide information on how to format the text on the page. This is because XML is meant to separate the data from display, allowing it to be used 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 [2] instead. Not only does this allow for the collection and storage of specific medical data fields as you might in a RDBMS, it provides additional flexibility to extend the document and add new types of data, even including digital signatures [3]. Using other technology, such as schemas, it's also possible to do validation on XML documents to ensure that parts or all of the document is structured in a certain way.

In addition to storage, XML is able to facilitate the exchange of medical information. While any standard for data exchange requires some agreed upon rules for how the data is organised, some older binary formats often relied on information to be stored in a particular order and constrained you to a certain length for your data. XML allows some flexibility in the order that data fields are organised, as well as the ability to accept data of any length. XML data can be even be created and sent over a standard internet connection and read by a web browser, unlike proprietary binary formats which more often required special server and client programs to be running to handle data transfers.

There are several different XML-based standards in healthcare, such as the HL7 v3 messaging standard [4] for exchanging medical information, as well as the HL7 Clinical Document Architecture (CDA) [5] and the ASTM Continuity of Care Record (CCR) [6] standards to store and exchange clinical information, all of which benefit from the power and flexibility of XML.

References

• W3C XML [1]
• XML databases [2]
• XML Digital Signature standard [3]
• HL7 v3 Messaging Standards [4]
• Clinical Document Architecture (CDA) [5]
• Continuity of Care Record (CCR) [6]

Submitted by Luke Rasmussen