XPaths

Question 1

XPath

Answer 1

Allows us to return a set of values or nodes from an XML document.

Question 2

What can be returned from an XPath?

Answer 2

• values, like strings or integers
• nodes, like document nodes, element nodes and attributes

Question 3

Basic XPath format

Answer 3

/E1/E2/E3/E4/…/En
Essentially, select all nodes reachable from the root by following the edges labelled as above.

Question 4

XPath example

Answer 4

If we had:

<students>
<student>
<name>Jane</name>
<number>75290</number>
</student>
</students>

We can do:
students/student

Resulting in all the student elements::

<student>
<name>Jane</name>
<number>75290</number>
</student>

Question 5

XPath Root Line

Answer 5

Any XPath should start with the documents name, for example:
students/student
should be
doc(“mydoc.xml”)/students/student

Question 6

XPath attribute

Answer 6

If we wanted to return the attribute values themselves, we would write:
/students/student/@name

If we were to write /students/student/name, it would return:

<name>"Sarah"</name>

But with the @ symbol we get:
“Sarah”

Depending on processing, we could also have to include /data() at the end.

Question 7

Advanced XPaths

Answer 7

Normally comes with the use of an axis. So the format changes from
/E1/E2/E3/E4/…/En
to
/axis1::E1/axis2::E2/axis3::E3/axis4::E4

We end on an E.

Question 7

XPath Wildcard

Answer 7

Represented with *.
Can be used to stand for any tag name or attribute name.

Using the attribute example:
/students/student/@name

This would result in:
/students/student/*

And both would return Sarah, SO LONG as there are no other attributes under student, as * would return them too.

Question 8

Axis

Answer 8

Used to determine the next item on the path. For example, if we had:
axis1::E1
and axis1 is an attribute, then E1 is the name of an attribute.
We can remember that the shorthand for attribute is by using the @ symbol, or @name as an example.

Question 9

Descendants axis

Answer 9

To represent a descendent, we can replace
/descendent::E
with
//E

Question 10

Descendent definition

Answer 10

Any number of outgoing arrows away, but at least one.
A way to see it is:
x is the parent of y / y is the child of x
x is the ancestor of y / y is the descendent of x

Question 11

Preceding sibling(s)

Answer 11

Nodes with the same parent which come before the node.

Question 12

Following sibling(s)

Answer 12

Nodes with the same parent which come after the node.

Question 13

Conditions

Answer 13

We can also add conditions:
/axis1::E1[c1]
in which if the condition is true, then continue the path.

Question 14

Conditions Examples

Answer 14

//book[category=”CS”]/title
This will look at all books which contain the category CS in one of their nodes and return the title of that book.

Question 15

//*[category=”CS” or category=”Sc-fi”][1]

Answer 15

Returns the first element which fulfils the category conditions.

Question 16

//*[category=”CS” or category=”Sc-fi”][last()]

Answer 16

Presuming last() returns the last number, if will return the last book that fulfills these conditions.

Question 17

//book[category[1]=”CS”]/title

Answer 17

Returns the titles of the books whose first category is CS.

Question 18

//[.=”Maths”]/ancestor::[2]

Answer 18

Finds the grandparent of an element containing Maths.
. can be used to represent an element.
2 is essentially used to find the ancestors ancestor, aka traversing the tree up two steps.