National Information Exchange Model (NIEM) Practical Implementer’s Course Notes – XML Conceptual Review (Lesson 2)

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.