The document summarizes key concepts about XPath including: 1) XPath provides a logical model for working with XML documents and uses nodes to represent XML in memory. 2) XPath expressions can be absolute or relative and are used to select nodes from an XML document. Common axes include child, attribute, and descendant. 3) Predicates can be used to filter node sets and select specific nodes based on values or location.

1. CIS-189

2.  XPath provides a logical model for working
with XML document
 Nodes are used to represent serialized XML
(in memory)
◦ Not all parts of XML document are represented (XML
declaration, DOCTYPE)
 XPath is used in combination with other tools
(such as XSLT)

3.  Legal XPath code is called an expression
◦ An XPath expression that return a node set is a
location path
 Expressions can be absolute and relative
◦ Absolute path includes a full definition of how to
find node
◦ Relative path is based on current context (location)

4.  Root node represents document
◦ Can have only one child node (document element)
 Element node represents elements
◦ QName (qualified name) includes namespace prefix and
element name
 Attribute node represent attributes
◦ Have name and value
◦ Are not represented as child nodes
 Text node represents text value of an element
◦ Does not have a name
 Namespace node gives access to the namespace URI
and prefix
 Comment node
 Processing Instruction Node

5.  Boolean
◦ Written as true() and false()
 String
 Number – floating point values
 Node-set – unordered set
◦ Follows document order

6.  Element node references can be spelled out
or abbreviated
/child::movies/child::movie/child::price
OR
/movies/movie/price
◦ child::nodename can also be written nodename
 Attribute node references
attribute::attributename
OR
@attributename

7.  self  following
 child  following-sibling
 attribute  namespace
 ancestor  parent
 ancestor-or-self  preceding
 descendant  preceding-sibling
 descendent-or-self

8.  Default axis
 Selects nodes that are immediate nodes of
context (current) node
 Can use * to refer to all child nodes

9. <movie> If context is movie
<title>Up</title>  Location path
<price>4.99</price child::copy (or
> copy) returns node
<copy>1</copy> set with both copy
<copy>2</copy> elements
 Location path
</movie>
child::* (or *)
returns node set
with title, price, 2
copy nodes

10.  Can use node() to return all child nodes
including comments, processing instructions,
and text nodes
 Can return just text nodes using text()
◦ Text nodes are unnamed

11.  Used to select attributes belonging to a
particular element node
 To return all attributes
◦ attribute::*
◦ @*
 To return particular attribute
◦ attribute::attributename
◦ @attributename

12.  Used to filter node sets
◦ Predicate similar to query criteria
 Can use specific values or location references

13. XML: Find 3rd Vehicle:
<vehicles> /vehicles/vehicle[2]
<vehicle model="camaro">
<year>1967</year> (1-based numbering)
<engine>327 v8</engine>
</vehicle> Find vehicles that are from ‘72:
<vehicle model="challenger"> /vehicles/vehicle/[year=‘1972’]
<year>1972</year>
<engine>383 v8</engine> (return a node set)
</vehicle>
<vehicle model="baja bug">
<year>multiple</year>
<engine>1200
opposing4</engine>
</vehicle>
</vehicles>