treeql(n)                     Tree Query Language                    treeql(n)



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NAME
       treeql - Query tree objects

SYNOPSIS
       package require Tcl  8.2

       package require snit

       package require struct::list

       package require struct::set

       package require treeql  ?1.3.1?

       treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?

       qo query args...

       qo result

       qo discard

_________________________________________________________________

DESCRIPTION
       This package provides objects which can be used to query and transform
       tree objects following the API of tree objects created by the package
       struct::tree.

       The tree query and manipulation language used here, TreeQL, is inspired
       by Cost (See section References for more information).

       treeql, the package, is a fairly thin query facility over tree-
       structured data types.  It implements an ordered set of nodes (really a
       list) which are generated and filtered through the application of
       TreeQL operators to each node in turn.

API
   TREEQL CLASS API
       The command treeql is a snit::type which implements the Treeql Query
       Language. This means that it follows the API for class commands as
       specified by the package snit.  Its general syntax is

       treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?
              The command creates a new tree query object and returns the
              fully qualified name of the object command as its result.  The
              API the returned command is following is described in the
              section TreeQL OBJECT API

              Each query object is associated with a single tree object. This
              is the object all queries will be run against.

              If the option -nodes was specified then its argument is treated
              as a list of nodes. This list is used to initialize the node
              set. It defaults to the empty list.

              If the option -query was specified then its argument will be
              interpreted as an object, the parent query of this query. It
              defaults to the object itself. All queries will be interpreted
              in the environment of this object.

              Any arguments coming after the options are treated as a query
              and run immediately, after the node set has been initialized.
              This uses the same syntax for the query as the method query.

              The operations of the TreeQL available for this are explained in
              the section about The Tree Query Language. This section also
              explains the term node set used above.

   TREEQL OBJECT API
       As treeql has been implemented in snit all the standard methods of
       snit-based classes are available to the user and therefore not listed
       here. Please read the documentation for snit for what they are and what
       functionality they provide

       The methods provided by the package treeql itself are listed and
       explained below.

       qo query args...
              This method interprets its arguments as a series of TreeQL
              operators and interpretes them from the left to right (i.e.
              first to last).  Note that the first operator uses the node set
              currently known to the object to perform its actions.  In other
              words, the node set is not cleared, or modified in other ways,
              before the query is run. This allows the user to run several
              queries one after the other and have each use the results of the
              last. Any initialization has to be done by any query itself,
              using TreeQL operators.  The result of the method is the node
              set after the last operator of the query has been executed.

              Note that uncaught errors will leave the node set of the object
              in an intermediate state, per the TreeQL operators which were
              executed successfully before the error occurred.

              The above means in detail that:

              [1]    The first argument is interpreted as the name of a query
                     operator, the number of arguments required by that
                     operator is then determined, and taken from the
                     immediately following arguments.

                     Because of this operators cannot have optional arguments,
                     all arguments have to be present as defined.  Failure to
                     do this will, at least, confuse the query interpreter,
                     but more likely cause errors.

              [2]    The operator is applied to the current node set, yielding
                     a new node set, and/or manipulating the tree object the
                     query object is connected to.

              [3]    The arguments used (i.e. operator name and arguments) are
                     removed from the list of method arguments, and then the
                     whole process is repeated from step [1], until the list
                     of arguments is empty or an error occurred.



                  # q is the query object.

                  q query root children get data

                  # The above query
                  # - Resets the node set to the root node - root
                  # - Adds the children of root to the set - children
                  # - Replaces the node set with the       - get data
                  #   values for the attribute 'data',
                  #   for all nodes in the set which
                  #   have such an attribute.
                  # - And returns this information.

                  # Below we can see the same query, but rewritten
                  # to show the structure as it is seen by the query
                  # interpreter.

                  q query \\
                    root \\
                    children \\
                    get data


       The operators of the TreeQL language available for this are explained
       in the section about The Tree Query Language. This section also
       explains the term node set used above.

       qo result
              This method returns a list containing the current node set.

       qo discard
              This method returns the current node set (like method result),
              but also destroys the query object (qo).  This is useful when
              constructing and using sub-queries (%AUTO% objects immediately
              destroyed after use).

THE TREE QUERY LANGUAGE
       This and the following sections specify the Tree Query Language used by
       the query objects of this package in detail.

       First we explain the general concepts underneath the language which are
       required to comprehend it. This is followed by the specifications for
       all the available query operators. They fall into eight categories, and
       each category has its own section.

       [1]    TreeQL Concepts

       [2]    Structural generators

       [3]    Attribute Filters

       [4]    Attribute Mutators

       [5]    Attribute String Accessors

       [6]    Sub-queries

       [7]    Node Set Operators

       [8]    Node Set Iterators

       [9]    Typed node support

   TREEQL CONCEPTS
       The main concept which has to be understood is that of the node set.
       Each query object maintains exactly one such node set, and essentially
       all operators use it and input argument and for their result.  This
       structure simply contains the handles of all nodes which are currently
       of interest to the query object.  To name it a set is a bit of a
       misnomer, because

       [1]    A node (handle) can occur in the structure more than once, and

       [2]    the order of nodes in the structure is important as well.
              Whenever an operator processes all nodes in the node set it will
              do so in the order they occur in the structure.

       Regarding the possible multiple occurrence of a node, consider a node
       set containing two nodes A and B, both having node P as their immediate
       parent. Application of the TreeQL operator "parent" will then add P to
       the new node set twice, once per node it was parent of. I.e. the new
       node set will then be {P P}.

   STRUCTURAL GENERATORS
       All tree-structural operators locate nodes in the tree based on a
       structural relation ship to the nodes currently in the set and then
       replace the current node set with the set of nodes found Nodes which
       fulfill such a relationship multiple times are added to the result as
       often as they fulfill the relationship.

       It is important to note that the found nodes are collected in a
       separate storage area while processing the node set, and are added to
       (or replacing) the current node set only after the current node set has
       been processed completely.  In other words, the new nodes are not
       processed by the operator as well and do not affect the iteration.

       When describing an operator the variable N will be used to refer to any
       node in the node set.

       ancestors
              Replaces the current node set with the ancestors for all nodes N
              in the node set, should N have a parent. In other words, nodes
              without a parent do not contribute to the new node set. In other
              words, uses all nodes on the path from node N to root, in this
              order (root last), for all nodes N in the node set. This
              includes the root, but not the node itself.

       rootpath
              Replaces the current node set with the ancestors for all nodes N
              in the node set, should N have a parent. In other words, nodes
              without a parent do not contribute to the new node set.  In
              contrast to the operator ancestors the nodes are added in
              reverse order however, i.e. the root node first.

       parent Replaces the current node set with the parent of node N, for all
              nodes N in the node set, should N have a parent. In other words,
              nodes without a parent do not contribute to the new node set.

       children
              Replaces the current node set with the immediate children of
              node N, for all nodes N in the node set, should N have children.
              In other words, nodes without children do not contribute to the
              new node set.

       left   Replaces the current node set with the previous/left sibling for
              all nodes N in the node set, should N have siblings to the left.
              In other words, nodes without left siblings do not contribute to
              the new node set.

       right  Replaces the current node set with the next/right sibling for
              all nodes N in the node set, should N have siblings to the
              right. In other words, nodes without right siblings do not
              contribute to the new node set.

       prev   Replaces the current node set with all previous/left siblings of
              node N, for all nodes N in the node set, should N have siblings
              to the left. In other words, nodes without left siblings are
              ignored. The left sibling adjacent to the node is added first,
              and the leftmost sibling last (reverse tree order).

       esib   Replaces the current node set with all previous/left siblings of
              node N, for all nodes N in the node set, should N have siblings
              to the left. In other words, nodes without left siblings are
              ignored. The leftmost sibling is added first, and the left
              sibling adjacent to the node last (tree order).

              The method name is a shorthand for Earlier SIBling.

       next   Replaces the current node set with all next/right siblings of
              node N, for all nodes N in the node set, should N have siblings
              to the right. In other words, nodes without right siblings do
              not contribute to the new node set. The right sibling adjacent
              to the node is added first, and the rightmost sibling last (tree
              order).

       root   Replaces the current node set with a node set containing a
              single node, the root of the tree.

       tree   Replaces the current node set with a node set containing all
              nodes found in the tree. The nodes are added in pre-order
              (parent first, then children, the latter from left to right,
              first to last).

       descendants
              Replaces the current node set with the nodes in all subtrees
              rooted at node N, for all nodes N in the node set, should N have
              children. In other words, nodes without children do not
              contribute to the new node set.

              This is like the operator children, but covers the children of
              children as well, i.e. all the proper descendants. "Rooted at N"
              means that N itself is not added to the new set, which is also
              implied by proper descendants.

       subtree
              Like operator descendants, but includes the node N. In other
              words:

              Replaces the current node set with the nodes of the subtree of
              node N, for all nodes N in the node set, should N have children.
              In other words, nodes without children do not contribute to the
              new node set. I.e this is like the operator children, but covers
              the children of children, etc. as well. "Of N" means that N
              itself is added to the new set.

       forward
              Replaces the current node set with the nodes in the subtrees
              rooted at the right siblings of node N, for all nodes N in the
              node set, should N have right siblings, and they children. In
              other words, nodes without right siblings, and them without
              children are ignored.

              This is equivalent to the operator sequence

              next descendants

       later  This is an alias for the operator forward.

       backward
              Replaces the current node set with the nodes in the flattened
              previous subtrees, in reverse tree order.

              This is nearly equivalent to the operator sequence

              prev descendants

              The only difference is that this uses the nodes in reverse
              order.

       earlier
              Replaces the current node set with the nodes in the flattened
              previous subtrees, in tree order.

              This is equivalent to the operator sequence

              prev subtree

   ATTRIBUTE FILTERS
       These operators filter the node set by reference to attributes of nodes
       and their properties. Filter means that all nodes not fulfilling the
       criteria are removed from the node set. In other words, the node set is
       replaced by the set of nodes fulfilling the filter criteria.

       hasatt attr
              Reduces the node set to nodes which have an attribute named
              attr.

       withatt attr value
              Reduces the node set to nodes which have an attribute named
              attr, and where the value of that attribute is equal to value
              (The "==" operator is string equal -nocase).

       withatt! attr val
              This is the same as withatt, but all nodes in the node set have
              to have the attribute, and the "==" operator is string equal,
              i.e. no -nocase.  The operator will fail with an error if they
              don't have the attribute.

       attof attr vals
              Reduces the node set to nodes which which have an attribute
              named attr and where the value of that attribute is contained in
              the list vals of legal values. The contained-in operator used
              here does glob matching (using the attribute value as pattern)
              and ignores the case of the attribute value, but not for the
              elements of vals.

       attmatch attr match
              Same as withatt, but string match is used as the "==" operator,
              and match is the pattern checked for.

              Note that match is a interpreted as a partial argument list for
              string match. This means that it is interpreted as a list
              containing the pattern, and the pattern element can be preceded
              by options understand by string match, like -nocase.  This is
              especially important should the pattern contain spaces. It has
              to be wrapped into a list for correct interpretation by this
              operator

   ATTRIBUTE MUTATORS
       These operators change node attributes within the underlying tree. In
       other words, all these operators have side effects.

       set attr val
              Sets the attribute attr to the value val, for all nodes N in the
              node set.  The operator will fail if a node does not have an
              attribute named attr. The tree will be left in a partially
              modified state.

       unset attr
              Unsets the attribute attr, for all nodes N in the node set.  The
              operator will fail if a node does not have an attribute named
              attr. The tree will be left in a partially modified state.

   ATTRIBUTE STRING ACCESSORS
       These operators retrieve the values of node attributes from the
       underlying tree. The collected results are stored in the node set, but
       are not actually nodes.

       In other words, they redefine the semantics of the node set stored by
       the query object to contain non-node data after their completion.

       The query interpreter will terminate after it has finished processing
       one of these operators, silently discarding any later query elements.
       It also means that our talk about maintenance of a node set is not
       quite true. It is a node set while the interpreter is processing
       commands, but can be left as an attribute value set at the end of query
       processing.

       string op attr
              Applies the string operator op to the attribute named attr, for
              all nodes N in the node set, collects the results of that
              application and places them into the node set.

              The operator will fail if a node does not have an attribute
              named attr.

              The argument op is interpreted as partial argument list for the
              builtin command string.  Its first word has to be any of the
              sub-commands understood by string.  This has to be followed by
              all arguments required for the subcommand, except the last.
              that last argument is supplied by the attribute value.

       get pattern
              For all nodes N in the node set it determines all their
              attributes with names matching the glob pattern, then the values
              of these attributes, at last it replaces the node set with the
              list of these attribute values.

       attlist
              This is a convenience definition for the operator getvals *. In
              other words, it replaces the node set with a list of the
              attribute values for all attributes for all nodes N in the node
              set.

       attrs glob
              Replaces the current node set with a list of attribute lists,
              one attribute list per for all nodes N in the node set.

       attval attname
              Reduces the current node set with the operator hasatt, and then
              replaces it with a list containing the values of the attribute
              named attname for all nodes N in the node set.

   SUB-QUERIES
       Sub-queries yield node sets which are then used to augment, reduce or
       replace the current node set.

       andq query
              Replaces the node set with the set-intersection of the node set
              generated by the sub-query query and itself.

              The execution of the sub-query uses the current node set as its
              own initial node set.

       orq query
              Replaces the node set with the set-union of the node set
              generated by the sub-query query and itself. Duplicate nodes are
              removed.

              The execution of the sub-query uses the current node set as its
              own initial node set.

       notq query
              Replaces the node set with the set of nodes generated by the
              sub-query query which are also not in the current node set. In
              other word the set difference of itself and the node set
              generated by the sub-query.

              The execution of the sub-query uses the current node set as its
              own initial node set.

   NODE SET OPERATORS
       These operators change the node set directly, without referring to the
       tree.

       unique Removes duplicate nodes from the node set, preserving order. In
              other words, the earliest occurrence of a node handle is
              preserved, every other occurrence is removed.

       select Replaces the current node set with a node set containing only
              the first node from the current node set

       transform query var body
              First it interprets the sub-query query, using the current node
              set as its initial node set.  Then it iterates over the result
              of that query, binding the handle of each node to the variable
              named in var, and executing the script body.  The collected
              results of these executions is made the new node set, replacing
              the current one.

              The script body is executed in the context of the caller.

       map var body
              Iterates over the current node set, binding the handle of each
              node to the variable named in var, and executing the script
              body.  The collected results of these executions is made the new
              node set, replacing the current one.

              The script body is executed in the context of the caller.

       quote val
              Appends the literal value val to the current node set.

       replace val
              Replaces the current node set with the literal list value val.

   NODE SET ITERATORS
       foreach query var body
              Interprets the sub-query query, then performs the equivalent of
              operator over on the nodes in the node set created by that
              query. The current node set is not changed, except through side
              effects from the script body.

              The script body is executed in the context of the caller.

       with query body
              Interprets the query, then runs the script body on the node set
              generated by the query. At last it restores the current node set
              as it was before the execution of the query.

              The script body is executed in the context of the caller.

       over var body
              Executes the script body for each node in the node set, with the
              variable named by var bound to the name of the current node.
              The script body is executed in the context of the caller.

              This is like the builtin foreach, with the node set as the
              source of the list to iterate over.

              The results of executing the body are ignored.

       delete Deletes all the nodes contained in the current node set from the
              tree.

   TYPED NODE SUPPORT
       These filters and accessors assume the existence of an attribute called
       @type, and are short-hand forms useful for cost-like tree query, html
       tree editing, and so on.

       nodetype
              Returns the node type of nodes.  Attribute string accessor. This
              is equivalent to

              get @type

       oftype t
              Reduces the node set to nodes whose type is equal to t, with
              letter case ignored.

       nottype t
              Reduces the node set to nodes whose type is not equal to t, with
              letter case ignored.

       oftypes attrs
              Reduces set to nodes whose @type is an element in the list attrs
              of types. The value of @type is used as a glob pattern, and
              letter case is relevant.

EXAMPLES
REFERENCES
       [1]    COST [http://wiki.tcl.tk/COST] on the Tcler's Wiki.

       [2]    TreeQL [http://wiki.tcl.tk/treeql] on the Tcler's Wiki. Discuss
              this package there.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category treeql of
       the Tcllib SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report
       any ideas for enhancements you may have for either package and/or
       documentation.

KEYWORDS
       Cost, DOM, TreeQL, XPath, XSLT, structured queries, tree, tree query
       language

CATEGORY
       Data structures

COPYRIGHT
       Copyright (c) 2004 Colin McCormack <coldstore@users.sourceforge.net>
       Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>




treeql                               1.3.1                           treeql(n)
