1XML::XQL(3)           User Contributed Perl Documentation          XML::XQL(3)
2
3
4

NAME

6       XML::XQL - A perl module for querying XML tree structures with XQL
7

SYNOPSIS

9        use XML::XQL;
10        use XML::XQL::DOM;
11
12        $parser = new XML::DOM::Parser;
13        $doc = $parser->parsefile ("file.xml");
14
15        # Return all elements with tagName='title' under the root element 'book'
16        $query = new XML::XQL::Query (Expr => "book/title");
17        @result = $query->solve ($doc);
18        $query->dispose; # Avoid memory leaks - Remove circular references
19
20        # Or (to save some typing)
21        @result = XML::XQL::solve ("book/title", $doc);
22
23        # Or (to save even more typing)
24        @result = $doc->xql ("book/title");
25

DESCRIPTION

27       The XML::XQL module implements the XQL (XML Query Language) proposal
28       submitted to the XSL Working Group in September 1998.  The spec can be
29       found at: <http://www.w3.org/TandS/QL/QL98/pp/xql.html> Most of the
30       contents related to the XQL syntax can also be found in the
31       XML::XQL::Tutorial that comes with this distribution.  Note that XQL is
32       not the same as XML-QL!
33
34       The current implementation only works with the XML::DOM module, but
35       once the design is stable and the major bugs are flushed out, other
36       extensions might follow, e.g. for XML::Grove.
37
38       XQL was designed to be extensible and this implementation tries to
39       stick to that.  Users can add their own functions, methods, comparison
40       operators and data types.  Plugging in a new XML tree structure (like
41       XML::Grove) should be a piece of cake.
42
43       To use the XQL module, either
44
45         use XML::XQL;
46
47       or
48
49         use XML::XQL::Strict;
50
51       The Strict module only provides the core XQL functionality as found in
52       the XQL spec. By default (i.e. by using XML::XQL) you get 'XQL+', which
53       has some additional features.
54
55       See the section "Additional Features in XQL+" for the differences.
56
57       This module is still in development. See the To-do list in XQL.pm for
58       what still needs to be done. Any suggestions are welcome, the sooner
59       these implementation issues are resolved, the faster we can all use
60       this module.
61
62       If you find a bug, you would do me great favor by sending it to me in
63       the form of a test case. See the file t/xql_template.t that comes with
64       this distribution.
65
66       If you have written a cool comparison operator, function, method or XQL
67       data type that you would like to share, send it to
68       tjmather@tjmather.com and I will add it to this module.
69

XML::XQL global functions

71       solve (QUERY_STRING, INPUT_LIST...)
72            @result = XML::XQL::solve ("doc//book", $doc);
73
74           This is provided as a shortcut for:
75
76            $query = new XML::XQL::Query (Expr => "doc//book");
77            @result = $query->solve ($doc);
78            $query->dispose;
79
80           Note that with XML::XQL::DOM, you can also write (see
81           XML::DOM::Node for details):
82
83            @result = $doc->xql ("doc//book");
84
85       setDocParser (PARSER)
86           Sets the XML::DOM::Parser that is used by the new XQL+ document()
87           method.  By default it uses an XML::DOM::Parser that was created
88           without any arguments, i.e.
89
90             $PARSER = new XML::DOM::Parser;
91
92       defineFunction (NAME, FUNCREF, ARGCOUNT [, ALLOWED_OUTSIDE [, CONST,
93       [QUERY_ARG]]])
94           Defines the XQL function (at the global level, i.e. for all newly
95           created queries) with the specified NAME. The ARGCOUNT parameter
96           can either be a single number or a reference to a list with
97           numbers.  A single number expands to [ARGCOUNT, ARGCOUNT]. The list
98           contains pairs of numbers, indicating the number of arguments that
99           the function allows. The value -1 means infinity. E.g. [2, 5, 7, 9,
100           12, -1] means that the function can have 2, 3, 4, 5, 7, 8, 9, 12 or
101           more arguments.  The number of arguments is checked when parsing
102           the XQL query string.
103
104           The second parameter must be a reference to a Perl function or an
105           anonymous sub. E.g. '\&my_func' or 'sub { ... code ... }'
106
107           If ALLOWED_OUTSIDE (default is 0) is set to 1, the function or
108           method may also be used outside subqueries in node queries.  (See
109           NodeQuery parameter in Query constructor)
110
111           If CONST (default is 0) is set to 1, the function is considered to
112           be "constant". See "Constant Function Invocations" for details.
113
114           If QUERY_ARG (default is 0) is not -1, the argument with that index
115           is considered to be a 'query parameter'. If the query parameter is
116           a subquery, that returns multiple values, the result list of the
117           function invocation will contain one result value for each value of
118           the subquery.  E.g. 'length(book/author)' will return a list of
119           Numbers, denoting the string lengths of all the author elements
120           returned by 'book/author'.
121
122           Note that only methods (not functions) may appear after a Bang "!"
123           operator.  This is checked when parsing the XQL query string.
124
125           See also: defineMethod
126
127       generateFunction (NAME, FUNCNAME, RETURN_TYPE [, ARGCOUNT [,
128       ALLOWED_OUTSIDE [, CONST [, QUERY_ARG]]]])
129           Generates and defines an XQL function wrapper for the Perl function
130           with the name FUNCNAME. The function name will be NAME in XQL query
131           expressions.  The return type should be one of the builtin XQL Data
132           Types or a class derived from XML::XQL::PrimitiveType (see "Adding
133           Data Types".)  See defineFunction for the meaning of ARGCOUNT,
134           ALLOWED_OUTSIDE, CONST and QUERY_ARG.
135
136           Function values are always converted to Perl strings with
137           xql_toString before they are passed to the Perl function
138           implementation. The function return value is cast to an object of
139           type RETURN_TYPE, or to the empty list [] if the result is undef.
140           It uses expandType to expand XQL primitive type names.  If
141           RETURN_TYPE is "*", it returns the function result as is, unless
142           the function result is undef, in which case it returns [].
143
144       defineMethod (NAME, FUNCREF, ARGCOUNT [, ALLOWED_OUTSIDE])
145           Defines the XQL method (at the global level, i.e. for all newly
146           created queries) with the specified NAME. The ARGCOUNT parameter
147           can either be a single number or a reference to a list with
148           numbers.  A single number expands to [ARGCOUNT, ARGCOUNT]. The list
149           contains pairs of numbers, indicating the number of arguments that
150           the method allows. The value -1 means infinity. E.g. [2, 5, 7, 9,
151           12, -1] means that the method can have 2, 3, 4, 5, 7, 8, 9, 12 or
152           more arguments.  The number of arguments is checked when parsing
153           the XQL query string.
154
155           The second parameter must be a reference to a Perl function or an
156           anonymous sub. E.g. '\&my_func' or 'sub { ... code ... }'
157
158           If ALLOWED_OUTSIDE (default is 0) is set to 1, the function or
159           method may also be used outside subqueries in node queries.  (See
160           NodeQuery parameter in Query constructor)
161
162           Note that only methods (not functions) may appear after a Bang "!"
163           operator.  This is checked when parsing the XQL query string.
164
165           See also: defineFunction
166
167       defineComparisonOperators (NAME => FUNCREF [, NAME => FUNCREF]*)
168           Defines XQL comparison operators at the global level.  The FUNCREF
169           parameters must be a references to a Perl function or an anonymous
170           sub. E.g. '\&my_func' or 'sub { ... code ... }'
171
172           E.g. define the operators $my_op$ and $my_op2$:
173
174            defineComparisonOperators ('my_op' => \&my_op,
175                                       'my_op2' => sub { ... insert code here ... });
176
177       defineElementValueConvertor (TAG_NAME, FUNCREF)
178           Defines that the result of the value() call for Elements with the
179           specified TAG_NAME uses the specified function. The function will
180           receive two parameters. The second one is the TAG_NAME of the
181           Element node and the first parameter is the Element node itself.
182           FUNCREF should be a reference to a Perl function, e.g. \&my_sub, or
183           an anonymous sub.
184
185           E.g. to define that all Elements with tag name 'date-of-birth'
186           should return XML::XQL::Date objects:
187
188                   defineElementValueConvertor ('date-of-birth', sub {
189                           my $elem = shift;
190                           # Always pass in the node as the second parameter. This is
191                           # the reference node for the object, which is used when
192                           # sorting values in document order.
193                           new XML::XQL::Date ($elem->xql_text, $elem);
194                   });
195
196           These convertors can only be specified at a global level, not on a
197           per query basis. To undefine a convertor, simply pass a FUNCREF of
198           undef.
199
200       defineAttrValueConvertor (ELEM_TAG_NAME, ATTR_NAME, FUNCREF)
201           Defines that the result of the value() call for Attributes with the
202           specified ATTR_NAME and a parent Element with the specified
203           ELEM_TAG_NAME uses the specified function. An ELEM_TAG_NAME of "*"
204           will match regardless of the tag name of the parent Element. The
205           function will receive 3 parameters. The third one is the tag name
206           of the parent Element (even if ELEM_TAG_NAME was "*"), the second
207           is the ATTR_NAME and the first is the Attribute node itself.
208           FUNCREF should be a reference to a Perl function, e.g. \&my_sub, or
209           an anonymous sub.
210
211           These convertors can only be specified at a global level, not on a
212           per query basis. To undefine a convertor, simply pass a FUNCREF of
213           undef.
214
215       defineTokenQ (Q)
216           Defines the token for the q// string delimiters at a global level.
217           The default value for XQL+ is 'q', for XML::XQL::Strict it is
218           undef.  A value of undef will deactivate this feature.
219
220       defineTokenQQ (QQ)
221           Defines the token for the qq// string delimiters at a global level.
222           The default value for XQL+ is 'qq', for XML::XQL::Strict it is
223           undef.  A value of undef will deactivate this feature.
224
225       expandType (TYPE)
226           Used internally to expand type names of XQL primitive types.  E.g.
227           it expands "Number" to "XML::XQL::Number" and is not case-
228           sensitive, so "number" and "NuMbEr" will both expand correctly.
229
230       defineExpandedTypes (ALIAS, FULL_NAME [, ...])
231           For each pair of arguments it allows the class name FULL_NAME to be
232           abbreviated with ALIAS. The definitions are used by expandType().
233           (ALIAS is always converted to lowercase internally, because
234           expandType is case-insensitive.)
235
236           Overriding the ALIAS for "date", also affects the object type
237           returned by the date() function.
238
239       setErrorContextDelimiters (START, END, BOLD_ON, BOLD_OFF)
240           Sets the delimiters used when printing error messages during query
241           evaluation.  The default delimiters on Unix are `tput smul`
242           (underline on) and `tput rmal` (underline off). On other systems
243           (that don't have tput), the delimiters are ">>" and "<<" resp.
244
245           When printing the error message, the subexpression that caused the
246           error will be enclosed by the delimiters, i.e. underlined on Unix.
247
248           For certain subexpressions the significant keyword, e.g. "$and$" is
249           enclosed in the bold delimiters BOLD_ON (default: `tput bold` on
250           Unix, "" elsewhere) and BOLD_OFF (default: (`tput rmul` . `tput
251           smul`) on Unix, "" elsewhere, see $BoldOff in XML::XQL::XQL.pm for
252           details.)
253
254       isEmptyList (VAR)
255           Returns 1 if VAR is [], else 0. Can be used in user defined
256           functions.
257

Additional Features in XQL+

259       Parent operator '..'
260           The '..' operator returns the parent of the current node, where '.'
261           would return the current node. This is not part of any XQL
262           standard, because you would normally use return operators, which
263           are not implemented here.
264
265       Sequence operators ';' and ';;'
266           The sequence operators ';' (precedes) and ';;' (immediately
267           precedes) are not in the XQL spec, but are described in 'The Design
268           of XQL' by Jonathan Robie who is one of the designers of XQL. It
269           can be found at <http://www.texcel.no/whitepapers/xql-design.html>
270           See also the XQL Tutorial for a description of what they mean.
271
272       q// and qq// String Tokens
273           String tokens a la q// and qq// are allowed. q// evaluates like
274           Perl's single quotes and qq// like Perl's double quotes. Note that
275           the default XQL strings do not allow escaping etc., so it's not
276           possible to define a string with both single and double quotes. If
277           'q' and 'qq' are not to your liking, you may redefine them to
278           something else or undefine them altogether, by assigning undef to
279           them. E.g:
280
281            # at a global level - shared by all queries (that don't (re)define 'q')
282            XML::XQL::defineTokenQ ('k');
283            XML::XQL::defineTokenQQ (undef);
284
285            # at a query level - only defined for this query
286            $query = new XML::XQL::Query (Expr => "book/title", q => 'k', qq => undef);
287
288           From now on k// works like q// did and qq// doesn't work at all
289           anymore.
290
291       Query strings can have embedded Comments
292           For example:
293
294            $queryExpr = "book/title          # this comment is inside the query string
295                          [. = 'Moby Dick']"; # this comment is outside
296
297       Optional dollar delimiters and case-insensitive XQL keywords
298           The following XQL keywords are case-insensitive and the dollar sign
299           delimiters may be omitted: $and$, $or$, $not$, $union$,
300           $intersect$, $to$, $any$, $all$, $eq$, $ne$, $lt$, $gt$, $ge$,
301           $le$, $ieq$, $ine$, $ilt$, $igt$, $ige$, $ile$.
302
303           E.g. $AND$, $And$, $aNd$, and, And, aNd are all valid replacements
304           for $and$.
305
306           Note that XQL+ comparison operators ($match$, $no_match$, $isa$,
307           $can$) still require dollar delimiters and are case-sensitive.
308
309       Comparison operator: $match$ or '=~'
310           E.g. "book/title =~ '/(Moby|Dick)/']" will return all book titles
311           containing Moby or Dick. Note that the match expression needs to be
312           quoted and should contain the // or m// delimiters for Perl.
313
314           When casting the values to be matched, both are converted to Text.
315
316       Comparison operator: $no_match$ or '!~'
317           E.g. "book/title !~ '/(Moby|Dick)/']" will return all book titles
318           that don't contain Moby or Dick. Note that the match expression
319           needs to be quoted and should contain the // or m// delimiters for
320           Perl.
321
322           When casting the values to be matched, both are converted to Text.
323
324       Comparison operator: $isa$
325           E.g. '//. $isa$ "XML::XQL::Date"' returns all elements for which
326           the value() function returns an XML::XQL::Date object. (Note that
327           the value() function can be overridden to return a specific object
328           type for certain elements and attributes.) It uses expandType to
329           expand XQL primitive type names.
330
331       Comparison operator: $can$
332           E.g. '//. $can$ "swim"' returns all elements for which the value()
333           function returns an object that implements the (Perl) swim()
334           method.  (Note that the value() function can be overridden to
335           return a specific object type for certain elements and attributes.)
336
337       Function: once (QUERY)
338           E.g. 'once(id("foo"))' will evaluate the QUERY expression only once
339           per query.  Certain query results (like the above example) will
340           always return the same value within a query. Using once() will
341           cache the QUERY result for the rest of the query.
342
343           Note that "constant" function invocations are always cached.  See
344           also "Constant Function Invocations"
345
346       Function: subst (QUERY, EXPR, EXPR [,MODIFIERS, [MODE]])
347           E.g. 'subst(book/title, "[M|m]oby", "Dick", "g")' will replace Moby
348           or moby with Dick globally ("g") in all book title elements.
349           Underneath it uses Perl's substitute operator s///. Don't worry
350           about which delimiters are used underneath.  The function returns
351           all the book/titles for which a substitution occurred.  The default
352           MODIFIERS string is "" (empty.) The function name may be
353           abbreviated to "s".
354
355           For most Node types, it converts the value() to a string (with
356           xql_toString) to match the string and xql_setValue to set the new
357           value in case it matched.  For XQL primitives (Boolean, Number,
358           Text) and other data types (e.g. Date) it uses xql_toString to
359           match the String and xql_setValue to set the result.  Beware that
360           performing a substitution on a primitive that was found in the
361           original XQL query expression, changes the value of that constant.
362
363           If MODE is 0 (default), it treats Element nodes differently by
364           matching and replacing text blocks occurring in the Element node. A
365           text block is defined as the concatenation of the raw text of
366           subsequent Text, CDATASection and EntityReference nodes. In this
367           mode it skips embedded Element nodes.  If a text block matches, it
368           is replaced by a single Text node, regardless of the original node
369           type(s).
370
371           If MODE is 1, it treats Element nodes like the other nodes, i.e. it
372           converts the value() to a string etc. Note that the default
373           implementation of value() calls text(), which normalizes whitespace
374           and includes embedded Element descendants (recursively.) This is
375           probably not what you want to use in most cases, but since I'm not
376           a professional psychic... :-)
377
378       Function: map (QUERY, CODE)
379           E.g. 'map(book/title, "s/[M|m]oby/Dick/g; $_")' will replace Moby
380           or moby with Dick globally ("g") in all book title elements.
381           Underneath it uses Perl's map operator. The function returns all
382           the book/titles for which a change occurred.
383
384           ??? add more specifics
385
386       Function: eval (EXPR [,TYPE])
387           Evaluates the Perl expression EXPR and returns an object of the
388           specified TYPE.  It uses expandType to expand XQL primitive type
389           names.  If the result of the eval was undef, the empty list [] is
390           returned.
391
392           E.g. 'eval("2 + 5", "Number")' returns a Number object with the
393           value 7, and
394                'eval("%ENV{USER}")' returns a Text object with the user name.
395
396           Consider using once() to cache the return value, when the
397           invocation will return the same result for each invocation within a
398           query.
399
400           ??? add more specifics
401
402       Function: new (TYPE [, QUERY [, PAR] *])
403           Creates a new object of the specified object TYPE. The constructor
404           may have any number of arguments. The first argument of the
405           constructor (the 2nd argument of the new() function) is considered
406           to be a 'query parameter'.  See defineFunction for a definition of
407           query parameter.  It uses expandType to expand XQL primitive type
408           names.
409
410       Function: document (QUERY) or doc (QUERY)
411           The document() function creates a new XML::XML::Document for each
412           result of QUERY (QUERY may be a simple string expression, like
413           "/usr/enno/file.xml".  See t/xql_document.t or below for an example
414           with a more complex QUERY.)
415
416           document() may be abbreviated to doc().
417
418           document() uses an XML::DOM::Parser underneath, which can be set
419           with XML::XQL::setDocParser(). By default it uses a parser that was
420           created without any arguments, i.e.
421
422             $PARSER = new XML::DOM::Parser;
423
424           Let's try a more complex example, assuming $doc contains:
425
426            <doc>
427             <file name="file1.xml"/>
428             <file name="file2.xml"/>
429            </doc>
430
431           Then the following query will return two XML::XML::Documents, one
432           for file1.xml and one for file2.xml:
433
434            @result = XML::XQL::solve ("document(doc/file/@name)", $doc);
435
436           The resulting documents can be used as input for following queries,
437           e.g.
438
439            @result = XML::XQL::solve ("document(doc/file/@name)/root/bla", $doc);
440
441           will return all /root/bla elements from the documents returned by
442           document().
443
444       Method: DOM_nodeType ()
445           Returns the DOM node type. Note that these are mostly the same as
446           nodeType(), except for CDATASection and EntityReference nodes.
447           DOM_nodeType() returns 4 and 5 respectively, whereas nodeType()
448           returns 3, because they are considered text nodes.
449
450       Function wrappers for Perl builtin functions
451           XQL function wrappers have been provided for most Perl builtin
452           functions.  When using a Perl builtin function like "substr" in an
453           XQL+ querry, an XQL function wrapper will be generated on the fly.
454           The arguments to these functions may be regular XQL+ subqueries
455           (that return one or more values) for a query parameter (see
456           generateFunction for a definition.)  Most wrappers of Perl builtin
457           functions have argument 0 for a query parameter, except for: chmod
458           (parameter 1 is the query parameter), chown (2) and utime (2).  The
459           following functions have no query parameter, which means that all
460           parameters should be a single value: atan2, rand, srand, sprintf,
461           rename, unlink, system.
462
463           The function result is casted to the appropriate XQL primitive type
464           (Number, Text or Boolean), or to an empty list if the result was
465           undef.
466
467   XPath functions and methods
468       The following functions were found in the XPath specification:
469
470       Function: concat (STRING, STRING, STRING*)
471           The concat function returns the concatenation of its arguments.
472
473       Function: starts-with (STRING, STRING)
474           The starts-with function returns true if the first argument string
475           starts with the second argument string, and otherwise returns
476           false.
477
478       Function: contains (STRING, STRING)
479           The contains function returns true if the first argument string
480           contains the second argument string, and otherwise returns false.
481
482       Function: substring-before (STRING, STRING)
483           The substring-before function returns the substring of the first
484           argument string that precedes the first occurrence of the second
485           argument string in the first argument string, or the empty string
486           if the first argument string does not contain the second argument
487           string. For example,
488
489            substring-before("1999/04/01","/") returns 1999.
490
491       Function: substring-after (STRING, STRING)
492           The substring-after function returns the substring of the first
493           argument string that follows the first occurrence of the second
494           argument string in the first argument string, or the empty string
495           if the first argument string does not contain the second argument
496           string. For example,
497
498            substring-after("1999/04/01","/") returns 04/01,
499
500           and
501
502            substring-after("1999/04/01","19") returns 99/04/01.
503
504       Function: substring (STRING, NUMBER [, NUMBER] )
505           The substring function returns the substring of the first argument
506           starting at the position specified in the second argument with
507           length specified in the third argument. For example,
508
509            substring("12345",2,3) returns "234".
510
511           If the third argument is not specified, it returns the substring
512           starting at the position specified in the second argument and
513           continuing to the end of the string. For example,
514
515            substring("12345",2) returns "2345".
516
517           More precisely, each character in the string is considered to have
518           a numeric position: the position of the first character is 1, the
519           position of the second character is 2 and so on.
520
521           NOTE: This differs from the substr method , in which the method
522           treats the position of the first character as 0.
523
524           The XPath spec says this about rounding, but that is not true in
525           this implementation: The returned substring contains those
526           characters for which the position of the character is greater than
527           or equal to the rounded value of the second argument and, if the
528           third argument is specified, less than the sum of the rounded value
529           of the second argument and the rounded value of the third argument;
530           the comparisons and addition used for the above follow the standard
531           IEEE 754 rules; rounding is done as if by a call to the round
532           function.
533
534       Method: string-length ( [ QUERY ] )
535           The string-length returns the number of characters in the string.
536           If the argument is omitted, it defaults to the context node
537           converted to a string, in other words the string-value of the
538           context node.
539
540           Note that the generated XQL wrapper for the Perl built-in substr
541           does not allow the argument to be omitted.
542
543       Method: normalize-space ( [ QUERY ] )
544           The normalize-space function returns the argument string with
545           whitespace normalized by stripping leading and trailing whitespace
546           and replacing sequences of whitespace characters by a single space.
547           Whitespace characters are the same as those allowed by the S
548           production in XML. If the argument is omitted, it defaults to the
549           context node converted to a string, in other words the string-value
550           of the context node.
551
552       Function: translate (STRING, STRING, STRING)
553           The translate function returns the first argument string with
554           occurrences of characters in the second argument string replaced by
555           the character at the corresponding position in the third argument
556           string. For example,
557
558            translate("bar","abc","ABC") returns the string BAr.
559
560           If there is a character in the second argument string with no
561           character at a corresponding position in the third argument string
562           (because the second argument string is longer than the third
563           argument string), then occurrences of that character in the first
564           argument string are removed. For example,
565
566            translate("--aaa--","abc-","ABC") returns "AAA".
567
568           If a character occurs more than once in the second argument string,
569           then the first occurrence determines the replacement character. If
570           the third argument string is longer than the second argument
571           string, then excess characters are ignored.
572
573           NOTE: The translate function is not a sufficient solution for case
574           conversion in all languages. A future version may provide
575           additional functions for case conversion.
576
577           This function was implemented using tr///d.
578
579       Function: sum ( QUERY )
580           The sum function returns the sum of the QUERY results, by
581           converting the string values of each result to a number.
582
583       Function: floor (NUMBER)
584           The floor function returns the largest (closest to positive
585           infinity) number that is not greater than the argument and that is
586           an integer.
587
588       Function: ceiling (NUMBER)
589           The ceiling function returns the smallest (closest to negative
590           infinity) number that is not less than the argument and that is an
591           integer.
592
593       Function: round (NUMBER)
594           The round function returns the number that is closest to the
595           argument and that is an integer. If there are two such numbers,
596           then the one that is closest to positive infinity is returned.
597

Implementation Details

599       XQL Builtin Data Types
600           The XQL engine uses the following object classes internally. Only
601           Number, Boolean and Text are considered primitive XQL types:
602
603           ·   XML::XQL::Number
604
605               For integers and floating point numbers.
606
607           ·   XML::XQL::Boolean
608
609               For booleans, e.g returned by true() and false().
610
611           ·   XML::XQL::Text
612
613               For string values.
614
615           ·   XML::XQL::Date
616
617               For date, time and date/time values. E.g. returned by the
618               date() function.
619
620           ·   XML::XQL::Node
621
622               Superclass of all XML node types. E.g. all subclasses of
623               XML::DOM::Node subclass from this.
624
625           ·   Perl list reference
626
627               Lists of values are passed by reference (i.e. using []
628               delimiters).  The empty list [] has a double meaning. It also
629               means 'undef' in certain situations, e.g. when a function
630               invocation or comparison failed.
631
632       Type casting in comparisons
633           When two values are compared in an XML comparison (e.g. $eq$) the
634           values are first casted to the same data type. Node values are
635           first replaced by their value() (i.e. the XQL value() function is
636           used, which returns a Text value by default, but may return any
637           data type if the user so chooses.)  The resulting values are then
638           casted to the type of the object with the highest xql_primType()
639           value. They are as follows: Node (0), Text (1), Number (2), Boolean
640           (3), Date (4), other data types (4 by default, but this may be
641           overriden by the user.)
642
643           E.g. if one value is a Text value and the other is a Number, the
644           Text value is cast to a Number and the resulting low-level (Perl)
645           comparison is (for $eq$):
646
647            $number->xql_toString == $text->xql_toString
648
649           If both were Text values, it would have been
650
651            $text1->xql_toString eq $text2->xql_toString
652
653           Note that the XQL spec is vague and even conflicting where it
654           concerns type casting. This implementation resulted after talking
655           to Joe Lapp, one of the spec writers.
656
657       Adding Data Types
658           If you want to add your own data type, make sure it derives from
659           XML::XQL::PrimitiveType and implements the necessary methods.
660
661           I will add more stuff here to explain it all, but for now, look at
662           the code for the primitive XQL types or the Date class
663           (XML::XQL::Date in Date.pm.)
664
665       Document Order
666           The XQL spec states that query results always return their values
667           in document order, which means the order in which they appeared in
668           the original XML document. Values extracted from Nodes (e.g. with
669           value(), text(), rawText(), nodeName(), etc.) always have a pointer
670           to the reference node (i.e. the Node from which the value was
671           extracted.) These pointers are acknowledged when (intermediate)
672           result lists are sorted. Currently, the only place where a result
673           list is sorted is in a $union$ expression, which is the only place
674           where the result list can be unordered.  (If you find that this is
675           not true, let me know.)
676
677           Non-node values that have no associated reference node, always end
678           up at the end of the result list in the order that they were added.
679           The XQL spec states that the reference node for an XML Attribute is
680           the Element to which it belongs, and that the order of values with
681           the same reference node is undefined. This means that the order of
682           an Element and its attributes would be undefined.  But since the
683           XML::DOM module keeps track of the order of the attributes, the XQL
684           engine does the same, and therefore, the attributes of an Element
685           are sorted and appear after their parent Element in a sorted result
686           list.
687
688       Constant Function Invocations
689           If a function always returns the same value when given "constant"
690           arguments, the function is considered to be "constant". A
691           "constant" argument can be either an XQL primitive (Number,
692           Boolean, Text) or a "constant" function invocation. E.g.
693
694            date("12-03-1998")
695            true()
696            sin(0.3)
697            length("abc")
698            date(substr("12-03-1998 is the date", 0, 10))
699
700           are constant, but not:
701
702            length(book[2])
703
704           Results of constant function invocations are cached and calculated
705           only once for each query. See also the CONST parameter in
706           defineFunction.  It is not necessary to wrap constant function
707           invocations in a once() call.
708
709           Constant XQL functions are: date, true, false and a lot of the XQL+
710           wrappers for Perl builtin functions. Function wrappers for certain
711           builtins are not made constant on purpose to force the invocation
712           to be evaluated every time, e.g. 'mkdir("/user/enno/my_dir",
713           "0644")' (although constant in appearance) may return different
714           results for multiple invocations.  See %PerlFunc in Plus.pm for
715           details.
716
717       Function: count ([QUERY])
718           The count() function has no parameters in the XQL spec. In this
719           implementation it will return the number of QUERY results when
720           passed a QUERY parameter.
721
722       Method: text ([RECURSE])
723           When expanding an Element node, the text() method adds the expanded
724           text() value of sub-Elements. When RECURSE is set to 0 (default is
725           1), it will not include sub-elements. This is useful e.g. when
726           using the $match$ operator in a recursive context (using the //
727           operator), so it won't return parent Elements when one of the
728           children matches.
729
730       Method: rawText ([RECURSE])
731           See text().
732

SEE ALSO

734       XML::XQL::Query, XML::XQL::DOM, XML::XQL::Date
735
736       The Japanese version of this document can be found on-line at
737       <http://member.nifty.ne.jp/hippo2000/perltips/xml/xql.htm>
738
739       The XML::XQL::Tutorial manual page. The Japanese version can be found
740       at <http://member.nifty.ne.jp/hippo2000/perltips/xml/xql/tutorial.htm>
741
742       The XQL spec at <http://www.w3.org/TandS/QL/QL98/pp/xql.html>
743
744       The Design of XQL at <http://www.texcel.no/whitepapers/xql-design.html>
745
746       The DOM Level 1 specification at <http://www.w3.org/TR/REC-DOM-Level-1>
747
748       The XML spec (Extensible Markup Language 1.0) at
749       <http://www.w3.org/TR/REC-xml>
750
751       The XML::Parser and XML::Parser::Expat manual pages.
752

AUTHOR

754       Enno Derksen is the original author.
755
756       Please send bugs, comments and suggestions to T.J. Mather
757       <tjmather@tjmather.com>
758
759
760
761perl v5.28.0                      2018-07-15                       XML::XQL(3)
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