Was quite baffled by
xpath(DOM, //div, DIV), being a syntax error until I realized div is an operator. xpath(DOM, //'div', DIV),
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Predicate xpath/3 |
[]
to select inside an
element. First we can construct paths using / and //:
//
Term/
Term
The Terms above are of type callable. The functor specifies
the element name. The element name’*’refers to any element.
The name self
refers to the top-element itself and is often
used for processing matches of an earlier xpath/3
query. A term NS:Term refers to an XML name in the namespace NS.
Optional arguments specify additional constraints and functions. The
arguments are processed from left to right. Defined conditional argument
values are:
last
last
- IntExprlast-1
is the element directly preceding the last one.index(Integer)
.last
index(last)
.last
- IntExprindex(last-IntExpr)
.Defined function argument values are:
self
content
text
text(As)
atom
or string
.normalize_space
text
, but uses normalize_space/2
to normalise white-space in the outputnumber
@
Attributelibrary(sgml)
.number
, but subsequently transform the value into an
integer using the round/1 function.number
, but subsequently transform the value into a
float using the float/1 function.@href
and
@href(atom)
are equivalent. The SGML parser can return
attributes as strings using the
attribute_value(string)
option.In addition, the argument-list can be conditions:
content = content
defines
that the content of the element is the atom content
. The
functions lower_case
and upper_case
can be
applied to Right (see example below).contains(Haystack, Needle)
h3
element
inside a div
element, where the div
element
itself contains an h2
child with a strong
child.
//div(h2/strong)/h3
This is equivalent to the conjunction of XPath goals below.
..., xpath(DOM, //(div), Div), xpath(Div, h2/strong, _), xpath(Div, h3, Result)
Examples:
Match each table-row in DOM:
xpath(DOM, //tr, TR)
Match the last cell of each tablerow in DOM. This example illustrates that a result can be the input of subsequent xpath/3 queries. Using multiple queries on the intermediate TR term guarantee that all results come from the same table-row:
xpath(DOM, //tr, TR), xpath(TR, /td(last), TD)
Match each href
attribute in an <a>
element
xpath(DOM, //a(@href), HREF)
Suppose we have a table containing rows where each first column is the name of a product with a link to details and the second is the price (a number). The following predicate matches the name, URL and price:
product(DOM, Name, URL, Price) :- xpath(DOM, //tr, TR), xpath(TR, td(1), C1), xpath(C1, /self(normalize_space), Name), xpath(C1, a(@href), URL), xpath(TR, td(2, number), Price).
Suppose we want to select books with genre="thriller" from a tree
containing elements <book genre=...>
thriller(DOM, Book) :- xpath(DOM, //book(@genre=thiller), Book).
Match the elements <table align="center">
and <table align="CENTER">
:
//table(@align(lower) = center)
Get the width
and height
of a div
element as a number, and the div
node itself:
xpath(DOM, //div(@width(number)=W, @height(number)=H), Div)
Note that div
is an infix operator, so parentheses must
be used in cases like the following:
xpath(DOM, //(div), Div)