XPath

San Skulrattanakulchai

May 14, 2019

XQuery and XPath Data Model (XDM)

XPath enables one to move from one xml element to other elements.
While SQL works with bags of tuples, XPath works with sequences of items.
An item is either
- a value of primitive type like integer, real, boolean, string
- a node is one of
  - elements
  - attributes
  - text
  - namespace
  - processing-instruction
  - comment
  - documents

Examples

These are items

10

"ten"

10.0

<Number base = "8">
    <Digit>1</Digit>
    <Digit>2</Digit>
</Number>

val="10"

Document Nodes

The syntax for making a document node is

doc(filename)

e.g.

doc("movies.xml")
doc("/Users/sam/data/movies.xml")
doc("infolab.stanford.du/~hector/movies.xml")

Path Expressions

A XPath path expression is very similar to a path expression for accessing files on Unix or Windows.
A path expression of the form /T1/T2/.../Tn means
- start at the document node
- successively process T1, then T2, …, until Tn
Example: Show how this works on /StarMovieData/Star/Name

Attributes in path expressions

Syntax
```
/T1/T2/.../Tn/@A
```
Show the result of
```
/StarMovieData/Star/@starID
```

Axes

Navigation through an XPath expression is along axes. Each axis has a full name and a short name. E.g. the path
```
/StarMovieData/Star/@starID
```
is actually short for
```
/child::StarMovieData/child::Star/attribute::starID
```
These are the 13 possible total axes (with shorthand if any):
- ancestor::
- ancestor-or-self::
- attribute:: @
- child::
- descendant::
- descendant-or-self:: //
- following::
- following-sibling::
- namespace::
- parent:: ..
- preceding::
- preceding-sibling::
- self:: .
Example: Show what //City returns.

Wildcards

Show the result of
```
/StarMovieData/*/@*
```

Operators

Operators that can be used in XPath expressions:
```
|
+
-
*
div
=
!=
<
<=
>
>=
or
and
mod
```

Conditions in XPath expression

Explain what these expressions return.

/StarMovieData/Star[//City="Malibu"]/Name

/Movies/Movie/Version[1]/@year

/Movies/Movie/Version[Star]