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/home/swipl/lib/swipl/library/xpath.pl
AllApplicationManualNameSummaryHelp

  • swipl
    • library
      • error.pl
      • apply.pl
      • lists.pl -- List Manipulation
      • debug.pl -- Print debug messages and test assertions
      • broadcast.pl -- Event service
      • socket.pl
      • predicate_options.pl
      • shlib.pl -- Utility library for loading foreign objects (DLLs, shared objects)
      • option.pl -- Option list processing
      • uid.pl -- User and group management on Unix systems
      • unix.pl -- Unix specific operations
      • syslog.pl -- Unix syslog interface
      • thread_pool.pl -- Resource bounded thread management
      • gensym.pl
      • settings.pl -- Setting management
      • arithmetic.pl -- Extensible arithmetic
      • main.pl -- Provide entry point for scripts
      • readutil.pl
      • ssl.pl
      • crypto.pl
      • filesex.pl
      • doc_http.pl -- Documentation server
      • pldoc.pl -- Process source documentation
      • operators.pl -- Manage operators
      • pairs.pl -- Operations on key-value lists
      • prolog_source.pl -- Examine Prolog source-files
      • sgml.pl -- SGML, XML and HTML parser
      • quasi_quotations.pl -- Define Quasi Quotation syntax
      • uri.pl -- Process URIs
      • url.pl -- Analysing and constructing URL
      • www_browser.pl -- Open a URL in the users browser
      • prolog_colour.pl
      • record.pl -- Access compound arguments by name
      • prolog_xref.pl -- Prolog cross-referencer data collection
      • occurs.pl -- Finding and counting sub-terms
      • ordsets.pl -- Ordered set manipulation
      • assoc.pl -- Binary associations
      • ugraphs.pl -- Graph manipulation library
      • memfile.pl
      • xpath.pl -- Select nodes in an XML DOM
        • xpath_chk/3
        • xpath/3
      • iostream.pl -- Utilities to deal with streams
      • atom.pl -- Operations on atoms
      • porter_stem.pl
      • solution_sequences.pl -- Modify solution sequences
      • prolog_pack.pl -- A package manager for Prolog
      • prolog_config.pl -- Provide configuration information
      • process.pl -- Create processes and redirect I/O
      • git.pl -- Run GIT commands
      • ctypes.pl -- Character code classification
      • time.pl -- Time and alarm library
      • utf8.pl -- UTF-8 encoding/decoding on lists of character codes.
      • base64.pl -- Base64 encoding and decoding
      • sha.pl -- SHA secure hashes
      • crypt.pl
      • persistency.pl -- Provide persistent dynamic predicates
      • pure_input.pl -- Pure Input from files and streams
      • nb_set.pl -- Non-backtrackable sets
      • xsdp_types.pl -- XML-Schema primitive types
      • uuid.pl -- Universally Unique Identifier (UUID) Library
      • pcre.pl -- Perl compatible regular expression matching for SWI-Prolog
      • aggregate.pl -- Aggregation operators on backtrackable predicates
      • rdf_write.pl -- Write RDF/XML from a list of triples
      • rdf.pl -- RDF/XML parser
      • sgml_write.pl -- XML/SGML writer module
      • archive.pl -- Access several archive formats
      • csv.pl -- Process CSV (Comma-Separated Values) data
      • dialect.pl -- Support multiple Prolog dialects
      • apply_macros.pl -- Goal expansion rules to avoid meta-calling
      • prolog_code.pl -- Utilities for reasoning about code
      • dif.pl -- The dif/2 constraint
      • thread.pl -- High level thread primitives
      • rdf_triple.pl -- Create triples from intermediate representation
      • rdf_parser.pl
      • rewrite_term.pl
      • rbtrees.pl -- Red black trees
      • nb_rbtrees.pl -- Non-backtrackable operations on red black trees
      • pengines.pl -- Pengines: Web Logic Programming Made Easy
      • yall.pl -- Lambda expressions
      • sandbox.pl -- Sandboxed Prolog code
      • prolog_format.pl -- Analyse format specifications
      • random.pl -- Random numbers
      • pengines_io.pl -- Provide Prolog I/O for HTML clients
      • zlib.pl -- Zlib wrapper for SWI-Prolog
      • bdb.pl -- Berkeley DB interface
      • hash_stream.pl -- Maintain a hash on a stream
      • md5.pl -- MD5 hashes
      • pprint.pl -- Pretty Print Prolog terms
      • modules.pl -- Module utility predicates
      • lazy_lists.pl -- Lazy list handling
      • edinburgh.pl -- Some traditional Edinburgh predicates
      • prolog_clause.pl -- Get detailed source-information about a clause
      • prolog_breakpoints.pl -- Manage Prolog break-points
      • dicts.pl -- Dict utilities
      • writef.pl -- Old-style formatted write
      • when.pl -- Conditional coroutining
      • codesio.pl -- I/O on Lists of Character Codes
      • qsave.pl -- Save current program as a state or executable
      • zip.pl -- Access resource ZIP archives
      • protobufs.pl -- Google's Protocol Buffers ("protobufs")
      • date.pl -- Process dates and times
      • charsio.pl -- I/O on Lists of Character Codes
      • odbc.pl
      • varnumbers.pl -- Utilities for numbered terms
      • table.pl
      • mqi.pl
      • term_to_json.pl
      • make.pl -- Reload modified source files
      • plunit.pl -- Unit Testing
      • hashtable.pl -- Hash tables
      • doc_latex.pl -- PlDoc LaTeX backend
      • jpl.pl -- A Java interface for SWI Prolog 7.x
      • isub.pl -- isub: a string similarity measure
      • unicode.pl -- Unicode string handling
      • check.pl -- Consistency checking
      • terms.pl -- Term manipulation
      • strings.pl -- String utilities
      • system.pl -- System utilities
      • quintus.pl -- Quintus compatibility
      • prolog_debug.pl -- User level debugging tools
      • portray_text.pl -- Portray text
      • sort.pl
      • listing.pl -- List programs and pretty print clauses
      • prolog_stream.pl -- A stream with Prolog callbacks
      • backcomp.pl -- Backward compatibility
      • statistics.pl -- Get information about resource usage
      • stomp.pl -- STOMP client.
      • threadutil.pl -- Interactive thread utilities
      • tables.pl -- XSB interface to tables
      • snowball.pl -- The Snowball multi-lingual stemmer library
      • streampool.pl -- Input multiplexing
      • cgi.pl -- Read CGI parameters
      • redis_streams.pl -- Using Redis streams
      • redis.pl -- Redis client
      • heaps.pl -- heaps/priority queues
      • udp_broadcast.pl -- A UDP broadcast proxy
      • intercept.pl -- Intercept and signal interface
      • shell.pl -- Elementary shell commands
      • xmldsig.pl -- XML Digital signature
      • prolog_profile.pl -- Execution profiler
      • base32.pl -- Base32 encoding and decoding
      • coinduction.pl -- Co-Logic Programming
      • wfs.pl -- Well Founded Semantics interface
      • prolog_stack.pl -- Examine the Prolog stack
      • ansi_term.pl -- Print decorated text to ANSI consoles
      • tty.pl -- Terminal operations
      • test_cover.pl -- Clause coverage analysis
      • editline.pl -- BSD libedit based command line editing
      • help.pl -- Text based manual
      • optparse.pl -- command line parsing
      • prolog_trace.pl -- Print access to predicates
      • edit.pl -- Editor interface
      • xmlenc.pl -- XML encryption library
      • prolog_codewalk.pl -- Prolog code walker
      • win_menu.pl -- Console window menu
      • c14n2.pl -- C14n2 canonical XML documents
      • yaml.pl -- Process YAML data
      • prolog_wrap.pl -- Wrapping predicates
      • explain.pl -- Describe Prolog Terms
      • fastrw.pl -- Fast reading and writing of terms
      • doc_files.pl -- Create stand-alone documentation files
      • files.pl
      • double_metaphone.pl -- Phonetic string matching
      • increval.pl -- Incremental dynamic predicate modification
      • pdt_console.pl
      • readline.pl -- GNU readline interface
      • paxos.pl -- A Replicated Data Store
      • streams.pl -- Manage Prolog streams
      • prolog_autoload.pl -- Autoload all dependencies
      • prolog_metainference.pl -- Infer meta-predicate properties
      • pwp.pl -- Prolog Well-formed Pages
      • prolog_jiti.pl -- Just In Time Indexing (JITI) utilities
      • oset.pl -- Ordered set manipulation
      • rlimit.pl
      • prolog_history.pl -- Per-directory persistent commandline history
 xpath(+DOM, +Spec, ?Content) is nondet
Match an element in a DOM structure. The syntax is inspired by XPath, using () rather than [] to select inside an element. First we can construct paths using / and //:
//Term
Select any node in the DOM matching term.
/Term
Match the root against Term.
Term
Select the immediate children of the root matching 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:

index(?Index)
True if the element is the Index-th child of its parent, where 1 denotes the first child. Index can be one of:
Var
Var is unified with the index of the matched element.
last
True for the last element.
last - IntExpr
True for the last-minus-nth element. For example, last-1 is the element directly preceding the last one.
IntExpr
True for the element whose index equals IntExpr.
Integer
The N-th element with the given name, with 1 denoting the first element. Same as index(Integer).
last
The last element with the given name. Same as index(last).
last - IntExpr
The IntExpr-th element before the last. Same as index(last-IntExpr).

Defined function argument values are:

self
Evaluate to the entire element
content
Evaluate to the content of the element (a list)
text
Evaluates to all text from the sub-tree as an atom
text(As)
Evaluates to all text from the sub-tree according to As, which is either atom or string.
normalize_space
As text, but uses normalize_space/2 to normalise white-space in the output
number
Extract an integer or float from the value. Ignores leading and trailing white-space
@Attribute
Evaluates to the value of the given attribute. Attribute can be a compound term. In this case the functor name denotes the element and arguments perform transformations on the attribute value. Defined transformations are:
number
Translate the value into a number using xsd_number_string/2 from library(sgml).
integer
As number, but subsequently transform the value into an integer using the round/1 function.
float
As number, but subsequently transform the value into a float using the float/1 function.
string
Translate the value into a Prolog string.
lower
Translate the value to lower case, preserving the type.
upper
Translate the value to upper case, preserving the type.

In addition, the argument-list can be conditions:

Left = Right
Succeeds if the left-hand unifies with the right-hand. If the left-hand side is a function, this is evaluated. The right-hand side is never evaluated, and thus the condition 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)
Succeeds if Needle is a sub-string of Haystack.
XPath
Succeeds if XPath matches in the currently selected sub-DOM. For example, the following expression finds an 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)
ClioPatria (version V3.1.1-42-gd6a756b-DIRTY)