Appendix C: XPath Expressions

XPath Expressions can be used when mapping system/project specific attributes from the source files to schematic or user defined database attributes. For further information, refer to XPath Expression Builder Dialog.

This Appendix provides a brief guide to the use of XPath Expressions. For further information refer to: http://www.w3.org/TR/xpath.

Within an Expression:

• XML element names are represented in their simplest form as the tag name, for example, <MyElement> is represented as MyElement.

• XML attribute names in their simplest form are prefixed with the @ character, for example, the attribute MyAttribute="value" is represented as @MyAttribute

• An expression is built up from a series of these LocationPaths separated by the ‘/’ character. For example the attribute from <MyElement @MyAttribute /> may be obtained using MyElement/@MyAttribute

• More complex LocationPaths exist, such as:

  Long Form	Short Form	Description
  child::MyElement	MyElement	MyElement child element of the current context.
  attribute::MyAttribute	@MyAttribute	MyAttribute XML attribute of the current context.
  child::*	*	All child elements of the current context.
  attribute::*	@	All attributes of the current context.
  parent::*	..	The parent element of the current context.
  ancestor::MyElement		The MyElement element that the current context is in.
  self ::*	.	The current context.
  /descendants::*	//*	All XML elements of the document.
  self::*//	//	All descendant XML element of the current context.
  following-sibling::*		The next XML element if one exists as a child of the same parent element.
  preceding-sibling::*		the previous element that is a child of the same parent element as the current context.

• Predicates can be added to each LocationPath in order to further constrain the selected nodes. Predicates are enclosed inside '[' and ']' characters. For example:

  MyElement[@MyAttribute] selects MyElement XML elements that have an attribute with the name MyAttribute

  MyElement[@MyAttribute = 'Motor'] selects the MyElement XML elements that have an attribute with the name MyAttribute that has a value of ‘Motor’

  MyElement[1] selects the first MyElement child of the current context

  MyElement[last()] selects the last MyElement child of the current context

• Data can then be manipulated using functions such as:

  normalize-space(MyElement) takes the textual contents from the MyElement element and replaces all whitespace with a single space character

  translate(MyElement/@Tag,'-','_') replaces and '-' characters with a '_' character from the Tag attribute of MyElement

  concat(MyElement[1],MyElement[2]) concatenates the results of MyElement[1] and MyElement[2]

  count(MyElement) The number of MyElement elements in the current context

  name(.) Name of the current element (including namespace)

  local-name(.) the local name of the current element (excluding namespace)

• A Boolean expression is one that returns a value of True or False. This is usually achieved using an equivalence or existence test such as:

  @MyAttribute = 'SomeValue' MyAttribute has a value of SomeValue

  @MyAttribute MyAttribute present on current context

  Count(MyElement) = 1 1 element named MyElement in the current context