1treeql(n) Tree Query Language treeql(n)
2______________________________________________________________________________
6
8 treeql - Query tree objects
9
11 package require Tcl 8.2
12 package require snit
14 package require struct::list
16 package require struct::set
18 package require treeql ?1.3.1?
20 treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?
22 qo query args...
24 qo result
26 qo discard
28______________________________________________________________________________
30
32 This package provides objects which can be used to query and transform
33 tree objects following the API of tree objects created by the package
34 struct::tree.
35 The tree query and manipulation language used here, TreeQL, is inspired
37 by Cost (See section References for more information).
38 treeql, the package, is a fairly thin query facility over tree-struc‐
40 tured data types. It implements an ordered set of nodes (really a
41 list) which are generated and filtered through the application of
42 TreeQL operators to each node in turn.
43
45 TREEQL CLASS API
46 The command treeql is a snit::type which implements the Treeql Query
47 Language. This means that it follows the API for class commands as
48 specified by the package snit. Its general syntax is
49 treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?
51 The command creates a new tree query object and returns the
52 fully qualified name of the object command as its result. The
53 API the returned command is following is described in the sec‐
54 tion TreeQL OBJECT API
55 Each query object is associated with a single tree object. This
57 is the object all queries will be run against.
58 If the option -nodes was specified then its argument is treated
60 as a list of nodes. This list is used to initialize the node
61 set. It defaults to the empty list.
62 If the option -query was specified then its argument will be
64 interpreted as an object, the parent query of this query. It
65 defaults to the object itself. All queries will be interpreted
66 in the environment of this object.
67 Any arguments coming after the options are treated as a query
69 and run immediately, after the node set has been initialized.
70 This uses the same syntax for the query as the method query.
71 The operations of the TreeQL available for this are explained in
73 the section about The Tree Query Language. This section also
74 explains the term node set used above.
75 TREEQL OBJECT API
77 As treeql has been implemented in snit all the standard methods of
78 snit-based classes are available to the user and therefore not listed
79 here. Please read the documentation for snit for what they are and what
80 functionality they provide
81 The methods provided by the package treeql itself are listed and
83 explained below.
84 qo query args...
86 This method interprets its arguments as a series of TreeQL oper‐
87 ators and interpretes them from the left to right (i.e. first to
88 last). Note that the first operator uses the node set currently
89 known to the object to perform its actions. In other words, the
90 node set is not cleared, or modified in other ways, before the
91 query is run. This allows the user to run several queries one
92 after the other and have each use the results of the last. Any
93 initialization has to be done by any query itself, using TreeQL
94 operators. The result of the method is the node set after the
95 last operator of the query has been executed.
96 Note that uncaught errors will leave the node set of the object
98 in an intermediate state, per the TreeQL operators which were
99 executed successfully before the error occurred.
100 The above means in detail that:
102 [1] The first argument is interpreted as the name of a query
104 operator, the number of arguments required by that opera‐
105 tor is then determined, and taken from the immediately
106 following arguments.
107 Because of this operators cannot have optional arguments,
109 all arguments have to be present as defined. Failure to
110 do this will, at least, confuse the query interpreter,
111 but more likely cause errors.
112 [2] The operator is applied to the current node set, yielding
114 a new node set, and/or manipulating the tree object the
115 query object is connected to.
116 [3] The arguments used (i.e. operator name and arguments) are
118 removed from the list of method arguments, and then the
119 whole process is repeated from step [1], until the list
120 of arguments is empty or an error occurred.
121 # q is the query object.
125 q query root children get data
127 # The above query
129 # - Resets the node set to the root node - root
130 # - Adds the children of root to the set - children
131 # - Replaces the node set with the - get data
132 # values for the attribute 'data',
133 # for all nodes in the set which
134 # have such an attribute.
135 # - And returns this information.
136 # Below we can see the same query, but rewritten
138 # to show the structure as it is seen by the query
139 # interpreter.
140 q query \\
142 root \\
143 children \\
144 get data
145 The operators of the TreeQL language available for this are explained
148 in the section about The Tree Query Language. This section also
149 explains the term node set used above.
150 qo result
152 This method returns a list containing the current node set.
153 qo discard
155 This method returns the current node set (like method result),
156 but also destroys the query object (qo). This is useful when
157 constructing and using sub-queries (%AUTO% objects immediately
158 destroyed after use).
159
161 This and the following sections specify the Tree Query Language used by
162 the query objects of this package in detail.
163 First we explain the general concepts underneath the language which are
165 required to comprehend it. This is followed by the specifications for
166 all the available query operators. They fall into eight categories, and
167 each category has its own section.
168 [1] TreeQL Concepts
170 [2] Structural generators
172 [3] Attribute Filters
174 [4] Attribute Mutators
176 [5] Attribute String Accessors
178 [6] Sub-queries
180 [7] Node Set Operators
182 [8] Node Set Iterators
184 [9] Typed node support
186 TREEQL CONCEPTS
188 The main concept which has to be understood is that of the node set.
189 Each query object maintains exactly one such node set, and essentially
190 all operators use it and input argument and for their result. This
191 structure simply contains the handles of all nodes which are currently
192 of interest to the query object. To name it a set is a bit of a mis‐
193 nomer, because
194 [1] A node (handle) can occur in the structure more than once, and
196 [2] the order of nodes in the structure is important as well. When‐
198 ever an operator processes all nodes in the node set it will do
199 so in the order they occur in the structure.
200 Regarding the possible multiple occurrence of a node, consider a node
202 set containing two nodes A and B, both having node P as their immediate
203 parent. Application of the TreeQL operator "parent" will then add P to
204 the new node set twice, once per node it was parent of. I.e. the new
205 node set will then be {P P}.
206 STRUCTURAL GENERATORS
208 All tree-structural operators locate nodes in the tree based on a
209 structural relation ship to the nodes currently in the set and then
210 replace the current node set with the set of nodes found Nodes which
211 fulfill such a relationship multiple times are added to the result as
212 often as they fulfill the relationship.
213 It is important to note that the found nodes are collected in a sepa‐
215 rate storage area while processing the node set, and are added to (or
216 replacing) the current node set only after the current node set has
217 been processed completely. In other words, the new nodes are not pro‐
218 cessed by the operator as well and do not affect the iteration.
219 When describing an operator the variable N will be used to refer to any
221 node in the node set.
222 ancestors
224 Replaces the current node set with the ancestors for all nodes N
225 in the node set, should N have a parent. In other words, nodes
226 without a parent do not contribute to the new node set. In other
227 words, uses all nodes on the path from node N to root, in this
228 order (root last), for all nodes N in the node set. This
229 includes the root, but not the node itself.
230 rootpath
232 Replaces the current node set with the ancestors for all nodes N
233 in the node set, should N have a parent. In other words, nodes
234 without a parent do not contribute to the new node set. In con‐
235 trast to the operator ancestors the nodes are added in reverse
236 order however, i.e. the root node first.
237 parent Replaces the current node set with the parent of node N, for all
239 nodes N in the node set, should N have a parent. In other words,
240 nodes without a parent do not contribute to the new node set.
241 children
243 Replaces the current node set with the immediate children of
244 node N, for all nodes N in the node set, should N have children.
245 In other words, nodes without children do not contribute to the
246 new node set.
247 left Replaces the current node set with the previous/left sibling for
249 all nodes N in the node set, should N have siblings to the left.
250 In other words, nodes without left siblings do not contribute to
251 the new node set.
252 right Replaces the current node set with the next/right sibling for
254 all nodes N in the node set, should N have siblings to the
255 right. In other words, nodes without right siblings do not con‐
256 tribute to the new node set.
257 prev Replaces the current node set with all previous/left siblings of
259 node N, for all nodes N in the node set, should N have siblings
260 to the left. In other words, nodes without left siblings are
261 ignored. The left sibling adjacent to the node is added first,
262 and the leftmost sibling last (reverse tree order).
263 esib Replaces the current node set with all previous/left siblings of
265 node N, for all nodes N in the node set, should N have siblings
266 to the left. In other words, nodes without left siblings are
267 ignored. The leftmost sibling is added first, and the left sib‐
268 ling adjacent to the node last (tree order).
269 The method name is a shorthand for Earlier SIBling.
271 next Replaces the current node set with all next/right siblings of
273 node N, for all nodes N in the node set, should N have siblings
274 to the right. In other words, nodes without right siblings do
275 not contribute to the new node set. The right sibling adjacent
276 to the node is added first, and the rightmost sibling last (tree
277 order).
278 root Replaces the current node set with a node set containing a sin‐
280 gle node, the root of the tree.
281 tree Replaces the current node set with a node set containing all
283 nodes found in the tree. The nodes are added in pre-order (par‐
284 ent first, then children, the latter from left to right, first
285 to last).
286 descendants
288 Replaces the current node set with the nodes in all subtrees
289 rooted at node N, for all nodes N in the node set, should N have
290 children. In other words, nodes without children do not contrib‐
291 ute to the new node set.
292 This is like the operator children, but covers the children of
294 children as well, i.e. all the proper descendants. "Rooted at N"
295 means that N itself is not added to the new set, which is also
296 implied by proper descendants.
297 subtree
299 Like operator descendants, but includes the node N. In other
300 words:
301 Replaces the current node set with the nodes of the subtree of
303 node N, for all nodes N in the node set, should N have children.
304 In other words, nodes without children do not contribute to the
305 new node set. I.e this is like the operator children, but covers
306 the children of children, etc. as well. "Of N" means that N
307 itself is added to the new set.
308 forward
310 Replaces the current node set with the nodes in the subtrees
311 rooted at the right siblings of node N, for all nodes N in the
312 node set, should N have right siblings, and they children. In
313 other words, nodes without right siblings, and them without
314 children are ignored.
315 This is equivalent to the operator sequence
317 next descendants
319 later This is an alias for the operator forward.
321 backward
323 Replaces the current node set with the nodes in the flattened
324 previous subtrees, in reverse tree order.
325 This is nearly equivalent to the operator sequence
327 prev descendants
329 The only difference is that this uses the nodes in reverse
331 order.
332 earlier
334 Replaces the current node set with the nodes in the flattened
335 previous subtrees, in tree order.
336 This is equivalent to the operator sequence
338 prev subtree
340 ATTRIBUTE FILTERS
342 These operators filter the node set by reference to attributes of nodes
343 and their properties. Filter means that all nodes not fulfilling the
344 criteria are removed from the node set. In other words, the node set is
345 replaced by the set of nodes fulfilling the filter criteria.
346 hasatt attr
348 Reduces the node set to nodes which have an attribute named
349 attr.
350 withatt attr value
352 Reduces the node set to nodes which have an attribute named
353 attr, and where the value of that attribute is equal to value
354 (The "==" operator is string equal -nocase).
355 withatt! attr val
357 This is the same as withatt, but all nodes in the node set have
358 to have the attribute, and the "==" operator is string equal,
359 i.e. no -nocase. The operator will fail with an error if they
360 don't have the attribute.
361 attof attr vals
363 Reduces the node set to nodes which which have an attribute
364 named attr and where the value of that attribute is contained in
365 the list vals of legal values. The contained-in operator used
366 here does glob matching (using the attribute value as pattern)
367 and ignores the case of the attribute value, but not for the
368 elements of vals.
369 attmatch attr match
371 Same as withatt, but string match is used as the "==" operator,
372 and match is the pattern checked for.
373 Note that match is a interpreted as a partial argument list for
375 string match. This means that it is interpreted as a list con‐
376 taining the pattern, and the pattern element can be preceded by
377 options understand by string match, like -nocase. This is espe‐
378 cially important should the pattern contain spaces. It has to be
379 wrapped into a list for correct interpretation by this operator
380 ATTRIBUTE MUTATORS
382 These operators change node attributes within the underlying tree. In
383 other words, all these operators have side effects.
384 set attr val
386 Sets the attribute attr to the value val, for all nodes N in the
387 node set. The operator will fail if a node does not have an
388 attribute named attr. The tree will be left in a partially modi‐
389 fied state.
390 unset attr
392 Unsets the attribute attr, for all nodes N in the node set. The
393 operator will fail if a node does not have an attribute named
394 attr. The tree will be left in a partially modified state.
395 ATTRIBUTE STRING ACCESSORS
397 These operators retrieve the values of node attributes from the under‐
398 lying tree. The collected results are stored in the node set, but are
399 not actually nodes.
400 In other words, they redefine the semantics of the node set stored by
402 the query object to contain non-node data after their completion.
403 The query interpreter will terminate after it has finished processing
405 one of these operators, silently discarding any later query elements.
406 It also means that our talk about maintenance of a node set is not
407 quite true. It is a node set while the interpreter is processing com‐
408 mands, but can be left as an attribute value set at the end of query
409 processing.
410 string op attr
412 Applies the string operator op to the attribute named attr, for
413 all nodes N in the node set, collects the results of that appli‐
414 cation and places them into the node set.
415 The operator will fail if a node does not have an attribute
417 named attr.
418 The argument op is interpreted as partial argument list for the
420 builtin command string. Its first word has to be any of the
421 sub-commands understood by string. This has to be followed by
422 all arguments required for the subcommand, except the last.
423 that last argument is supplied by the attribute value.
424 get pattern
426 For all nodes N in the node set it determines all their
427 attributes with names matching the glob pattern, then the values
428 of these attributes, at last it replaces the node set with the
429 list of these attribute values.
430 attlist
432 This is a convenience definition for the operator getvals *. In
433 other words, it replaces the node set with a list of the
434 attribute values for all attributes for all nodes N in the node
435 set.
436 attrs glob
438 Replaces the current node set with a list of attribute lists,
439 one attribute list per for all nodes N in the node set.
440 attval attname
442 Reduces the current node set with the operator hasatt, and then
443 replaces it with a list containing the values of the attribute
444 named attname for all nodes N in the node set.
445 SUB-QUERIES
447 Sub-queries yield node sets which are then used to augment, reduce or
448 replace the current node set.
449 andq query
451 Replaces the node set with the set-intersection of the node set
452 generated by the sub-query query and itself.
453 The execution of the sub-query uses the current node set as its
455 own initial node set.
456 orq query
458 Replaces the node set with the set-union of the node set gener‐
459 ated by the sub-query query and itself. Duplicate nodes are
460 removed.
461 The execution of the sub-query uses the current node set as its
463 own initial node set.
464 notq query
466 Replaces the node set with the set of nodes generated by the
467 sub-query query which are also not in the current node set. In
468 other word the set difference of itself and the node set gener‐
469 ated by the sub-query.
470 The execution of the sub-query uses the current node set as its
472 own initial node set.
473 NODE SET OPERATORS
475 These operators change the node set directly, without referring to the
476 tree.
477 unique Removes duplicate nodes from the node set, preserving order. In
479 other words, the earliest occurrence of a node handle is pre‐
480 served, every other occurrence is removed.
481 select Replaces the current node set with a node set containing only
483 the first node from the current node set
484 transform query var body
486 First it interprets the sub-query query, using the current node
487 set as its initial node set. Then it iterates over the result
488 of that query, binding the handle of each node to the variable
489 named in var, and executing the script body. The collected
490 results of these executions is made the new node set, replacing
491 the current one.
492 The script body is executed in the context of the caller.
494 map var body
496 Iterates over the current node set, binding the handle of each
497 node to the variable named in var, and executing the script
498 body. The collected results of these executions is made the new
499 node set, replacing the current one.
500 The script body is executed in the context of the caller.
502 quote val
504 Appends the literal value val to the current node set.
505 replace val
507 Replaces the current node set with the literal list value val.
508 NODE SET ITERATORS
510 foreach query var body
511 Interprets the sub-query query, then performs the equivalent of
512 operator over on the nodes in the node set created by that
513 query. The current node set is not changed, except through side
514 effects from the script body.
515 The script body is executed in the context of the caller.
517 with query body
519 Interprets the query, then runs the script body on the node set
520 generated by the query. At last it restores the current node set
521 as it was before the execution of the query.
522 The script body is executed in the context of the caller.
524 over var body
526 Executes the script body for each node in the node set, with the
527 variable named by var bound to the name of the current node.
528 The script body is executed in the context of the caller.
529 This is like the builtin foreach, with the node set as the
531 source of the list to iterate over.
532 The results of executing the body are ignored.
534 delete Deletes all the nodes contained in the current node set from the
536 tree.
537 TYPED NODE SUPPORT
539 These filters and accessors assume the existence of an attribute called
540 @type, and are short-hand forms useful for cost-like tree query, html
541 tree editing, and so on.
542 nodetype
544 Returns the node type of nodes. Attribute string accessor. This
545 is equivalent to
546 get @type
548 oftype t
550 Reduces the node set to nodes whose type is equal to t, with
551 letter case ignored.
552 nottype t
554 Reduces the node set to nodes whose type is not equal to t, with
555 letter case ignored.
556 oftypes attrs
558 Reduces set to nodes whose @type is an element in the list attrs
559 of types. The value of @type is used as a glob pattern, and let‐
560 ter case is relevant.
561
563 ... TODO ...
564
566 [1] COST [http://wiki.tcl.tk/COST] on the Tcler's Wiki.
567 [2] TreeQL [http://wiki.tcl.tk/treeql] on the Tcler's Wiki. Discuss
569 this package there.
570
572 This document, and the package it describes, will undoubtedly contain
573 bugs and other problems. Please report such in the category treeql of
574 the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
575 also report any ideas for enhancements you may have for either package
576 and/or documentation.
577 When proposing code changes, please provide unified diffs, i.e the out‐
579 put of diff -u.
580 Note further that attachments are strongly preferred over inlined
582 patches. Attachments can be made by going to the Edit form of the
583 ticket immediately after its creation, and then using the left-most
584 button in the secondary navigation bar.
585
587 Cost, DOM, TreeQL, XPath, XSLT, structured queries, tree, tree query
588 language
589
591 Data structures
592
594 Copyright (c) 2004 Colin McCormack <coldstore@users.sourceforge.net>
595 Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>
596tcllib 1.3.1 treeql(n)