NIEM Practical Implementer’s Course
Lesson 2 – XML Conceptual Review

Core Definitions

• Elements: The tags that exist within an XML document, collectively termed the “markup”. Types of elements include root, parent, and child.
• Attributes: Part(s) of an XML element that provide(s) additional information about that element. Attributes are defined and written as a name/value pair (e.g. name=”value” ).
• Instance: A document containing XML tags and content that results from use of XML schema rules.
• Well-Formed Instance: An XML instance is “well-formed” if it uses the correct syntax and structure as defined by XML standard(s) being used and meets the minimum criteria for XML parsers to read the document.

General Notes

• Rules/Guidelines for XML Elements
  • Can contain letters, numbers, and other characters.
  • Must not start with number or punctuation.
  • Must not start with xml, XML, or Xml.
  • Cannot contain spaces.
  • Should be descriptive to contained information.
  • Avoid dashes, colons, and periods (allowed, but usually are reserved for namespaces).
  • Avoid non-English letters/characters (allowed, but may not always be supported).
• XML Prolog & Processing Instructions
  • Prolog specifies the version and the character encoding used for the XML instance and should always come first in every document.
  • Processing instructions are used to associate presentation and/or transformation files with the data.
• XML Comments
  • Start with “<!– ” and end with ” –>”
  • Can include linebreaks.

Note: Information is being shared under the Creative Commons Attribution-ShareAlike 2.0 (CC BY-SA) license. Original content was created by NIEM course instructors Jenness, Owen, and Carlson.