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REBOL [ Library: [ level: 'intermediate platform: 'all type: tool domain: [ai xml] tested-under: none support: none license: none see-also: none ] History: [ [0.1 04-mar-2007 "First version"] [0.2 05-mar-2007 "Minor modification"] [0.3 06-mar-2007 "Improvement of the xpath_rules. Thanks to Marco."] [0.4 08-mar-2007 "Modification to remove a small bug introduced in v0.3."] [1.0 10-mar-2007 "handle attributes and empty elements"] ] Title: "xpath.r" Date: 03-march-2007 File: %xpath.r Author: "Alban Gabillon" Version: 1.0 Purpose: { This script shows how to implement an XPath interpreter in Rebol/Prolog. This interpreter is not complete. It is only a kind of "Proof of Concept". It lacks some features. Currently it can parse a document containing elements, attributes and pcdata. In this script I see an xml document as a tree of UNTYPED nodes. Consequently, - all nodes are treated the same, In particular attributes of an element are seen as child nodes of that element - the syntax DOES NOT FOLLOW exactly the XPath syntax (See the EXAMPLES below to understand how it works). Note1: It could be perfectly possible to directly parse XML data instead of rebxml data but it would be more difficult to write the parse_doc function. A solution could be to adapt xml2rebxml so that it produces the db atomic facts.}] samplexml: { <movie> <title>Star Trek: Insurrection</title> <star sex="M" age="35">Patrick Stewart</star> <star sex="M" age="25">Brent Spiner</star> <theater opening_year="2005"> <theater-name>MonoPlex 2000</theater-name> <showtime>14:15</showtime> <showtime>16:30</showtime> <showtime>18:45</showtime> <showtime>21:00</showtime> <price> <adult>$8.50</adult> <child>$5.00</child> </price> </theater> <theater opening_year="2006"> <theater-name>Bigscreen 1</theater-name> <showtime>19:30</showtime> <showtime/> <price>$6.00</price> </theater> <theater opening_year="2010" /> </movie> } examples: {EXAMPLES: For selecting the theaters ---------------------------------------------. XPath==> /movie/theater For selecting all the stars ---------------------------------------- XPath==> //star For selecting the first showtime of all theaters ------------------------------------------------------------------------ XPath==>//theater/showtime(1) For selecting all the showtimes of the second theater ------------------------------------------------------------------------------------ XPath==>//theater(2)/showtime For selecting all the male stars ------------------------------------------------ XPath==> //star[./sex/M] For selecting all the showtimes of the Bigscreen1 theater ----------------------------------------------------------------------------------------- XPath==>//theater[./theater-name/Bigscreen 1]/showtime OR XPath==>//theater[.//Bigscreen 1]/showtime For selecting the theaters with a showtime at 21:00 -------------------------------------------------------------------------------- XPath==>//theater[./showtime/21:00] } do do parsepath: func [ "parse an xpath expression - output is a block [pathup axis nodetest predicate position]" string [string!] /local workstring pathup test predicate position axis result][ either string = "root" [result: copy ["root" "" "" "" ""]][ predicate: position: "" workstring: reverse copy string switch first workstring [ #"]" [; there is a predicate tied to the nodetest predicate: copy "" rec: 1 while [rec > 0][ workstring: next workstring if workstring/1 = #"]" [rec: rec + 1] if workstring/1 = #"[" [rec: rec - 1] either rec > 0 [append predicate workstring/1][workstring: next workstring]] reverse predicate] #")" [; there is a position tied to the nodetest position: copy "" workstring: next workstring parse workstring [copy position to "(" thru "(" mark:] position: to-integer reverse position workstring: mark]] ; nodetest parse workstring [copy test to "/" mark:] reverse test ; pathup and axis workstring: mark workstring: next workstring either workstring/1 = #"/" [axis: copy "//" pathup: copy next workstring][axis: copy "/" pathup: copy workstring] reverse pathup result: copy reduce [pathup axis test predicate position]]] parse-doc: func [ "parse the rebxml block and create db atomic facts" parent [block!] "parent block" data [block!] "child block" /local element pcdata attribute value subtree elementlist search pos][ element: pcdata: attribute: value: subtree: none elementlist: copy [] parse data [ any [element: word! ; element (either search: find elementlist element/1 [ pos: search/2: search/2 + 1][ pos: 1 append elementlist reduce [element/1 1]] append db_facts compose/deep/only [index [(element) (pos)]] append db_facts compose/deep/only [child [(element) (parent)]]) any [attribute: word! value: string! ; attribute/value (append db_facts compose/deep/only [child [(attribute) (element)]] append db_facts compose/deep/only [child [(value) (attribute)]])] [subtree: block! (parse-doc element subtree/1) ; subtree | skip] ; empty tag (skip is for parsing /) | pcdata: string! ;pcdata (append db_facts compose/deep/only [child [(pcdata) (parent)]]) ] ] ] prompt: has [expression s e][ expression: copy "" expression: ask "XPath==> " either not empty? expression [ r: 0 for-which db [X][ xpath [expression X] ][ parse X compose/deep [ ; element (empty or not) s: word! any [word! string!] [block! | (to-lit-word "/")] e: | ;attribute s: word! string! e: | ;pcdata or attribute value s: string! e: ] probe copy/part s e r: r + 1 ] print [r "solution(s)"] false ][true] ] db_facts: copy [] xmldata: copy samplexml space: charset " ^/^M^-" parse xmldata [any [ ">" s: some space e: (s: remove/part s e) :s | s: some space e: "<" (s: remove/part s e) :s | skip ]] print "" print "INITIALIZATION OF THE KNOWLEDGE BASE - PLEASE BE PATIENT" print "" ; create the document root (not to confuse with the element root) doc: copy [/] doc: append/only doc xml2rebxml xmldata probe doc ;create database atomic facts parse-doc doc doc/2 db: assert none [xml [doc]] assert db db_facts comment {COMMENT lines between ============ and UNCOMMENT lines between *************** if you want as much deduction as possible (but low performances)} ;======================================= tree_geometry_rules: assert none [ descendant [X Y][ db/child [X Y] ] descendant [X Y][ db/child [X Z] descendant[Z Y] ] ] for-which tree_geometry_rules [X Y] [ descendant [X Y] ][ assert db compose/deep/only [descendant [(X) (Y)]] ] ;======================================= ;**************************************************************** ;tree_geometry_rules: [ ; descendant [X Y][ ; child [X Y]] ; descendant [X Y][ ; child [X Z] ; descendant[Z Y]]] ; assert db tree_geometry_rules ;**************************************************************** ;create xpath rules xpath_rules: [ xpath ["/" X][ xp [["root" "" "" "" ""] X]] xp [["root" "" "" "" ""] doc][ xml [X]] ; for not having path starting with / (would be more difficult to handle in the parsepath function) xpath [P X][ xp [(parsepath join "root" P) X]] ; child axis xp [[Pathup "/" Test "" ""] X][ xp [(parsepath Pathup) Y] child [X Y] equal? [(to-string X/1) Test]] ; descendant axis xp [[Pathup "//" Test "" ""] X][ xp [(parsepath Pathup) Y] descendant [X Y] equal? [(to-string X/1) Test]] ; nodetest tied with a position xp [[P1 P2 P3 _ Pos] X][ not-equal? ["" Pos] xp [(parsepath join P1 [P2 P3]) X] index [X Pos]] ; nodetest tied with a predicate (i.e. a path relative to the context node . (dot)) xp [[P1 P2 P3 P4 _] X][ not-equal? ["" P4] xp [(parsepath join P1 [P2 P3]) X] xp [(parsepath join P1 [P2 P3 next P4]) Y] descendant[Y X]] ] assert db xpath_rules print samplexml print examples print "press ENTER to leave the interpreter" until [prompt]
halt ;; to terminate script if DO'ne from webpage
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