M.Sc. of Advanced Software Engineering

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• M.Sc. of Advanced Software Engineering CO7206Sy
  stem Reengineering XPath
• Many Slides are by Georgios Koutsoukos

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Objectives

• To give some knowledge about core technologies
  used in CARE
• This lecture covers
• XPath

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Outline

• XPath basics
• XPath axes
• XPath examples

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Useful links

• Useful links
• http//www.w3schools.com/xpath/default.asp
• http//msdn.microsoft.com/library/default.asp?url
  /library/en-us/xmlsdk/html/1431789e-c545-4765-8c09
  -3057e07d3041.asp
• http//www.mulberrytech.com/quickref/XSLTquickref.
  pdf

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XPath Basics (1)

• XPath is a language for specifying parts of an
  XML document
• XPath uses path expressions to identify XML
  document parts. When evaluated, the expression
  returns an object that can be of type node-set (a
  group of nodes of the XML document tree
  structure), boolean, number, or string.
  Expressions are evaluated within a context.

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XPath Basics (2)

• A path expression is typically constructed from
  steps, which include
• an axis, specifying the tree relationships
  between the nodes
• a node test, specifying the name of the selected
  nodes and
• zero or more predicates, which refine the set of
  nodes selected.
• For example, in the expression
• childpetattributeType"dog" child
  specifies the axis, pet the node test and ...
  the predicate. Abbreviated syntax is also
  used, for instance "_at_Type" instead of
  "attributeType", "/pet" instead of "childpet"
  (and others).

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XPath Basics (3)

• XPath also inludes a library of standard
  functions for node-sets, strings, boolean and
  numbers.
• L-CARE provides an, extension to XPath, set of
  functions, for performing various operations. For
  instance
• boolean cmpIgnoreCase(String s1, String s2) for
  case-insensitive string comparison.
• int startLine(Node node) for getting the line
  where a statement represented by XML "Node"
  begins
• int sizeInLines(Node n) for getting the size in
  lines of code of a statement represented by XML
  "Node"

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XPath axes

• The axes in XPath are shown in the picture below
  (attributes and namespaces are not shown).

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XPath examples (1)

• The following XML document example is the one
  used on the introduction to XML.
• lt?xml version"1.0" encoding"iso-8859-1"?gt
  ltpetsgt ltpet type"dog" color"brown"gtMaxlt/petgt
  ltpet type"cat" color"white"gtToulalt/petgt
  lt/petsgt
• We will now demonstrate some very simple XPath
  examples using that document.

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XPath examples (2)

• Select all pet elements
• //pet or alternatively /pets/pet or
  /pets/child
• Select the first pet
• /pets/pet1
• Select all pets of type dog
• //pet_at_type "dog"
• Select all pets of white color
• //pet_at_color"white"
• Select the color of all dogs
• //pet_at_type "dog"/_at_color
• Get the types of pets with the name Max
• /pets/pettext()"Max"/_at_type

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Key Points

• XPath is an efective and powerful way of query
  XML documents.
• At this point you should have a basic idea about
  what XML and XPath is all about.
• It is VERY IMPORTANT that BEFORE next weeks
  tutorial on L-CARE you feel quite confortable
  using XPath, so PLEASE take a couple of hours on
  your own practicing it.

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Contacts

• Mailtormc20_at_le.ac.uk
• Office G3 (Usually I am there)
• Dr. El-Ramly is pleased to help