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RuleBasedTransliterator Class Reference

RuleBasedTransliterator is a transliterator that reads a set of rules in order to determine how to perform translations. More...

#include <rbt.h>

Class diagram for RuleBasedTransliterator:

Transliterator

List of all members.


Public Members

enum  { PARSE_ERROR_BASE, BAD_VARIABLE_DEFINITION, MALFORMED_RULE, MALFORMED_SET, MALFORMED_SYMBOL_REFERENCE, MALFORMED_UNICODE_ESCAPE, MALFORMED_VARIABLE_DEFINITION, MALFORMED_VARIABLE_REFERENCE, MISMATCHED_SEGMENT_DELIMITERS, MISPLACED_CURSOR_OFFSET, MISSING_OPERATOR, MISSING_SEGMENT_CLOSE, MULTIPLE_ANTE_CONTEXTS, MULTIPLE_CURSORS, MULTIPLE_POST_CONTEXTS, TRAILING_BACKSLASH, UNDEFINED_SEGMENT_REFERENCE, UNDEFINED_VARIABLE, UNQUOTED_SPECIAL, UNTERMINATED_QUOTE }
Parse error codes generated by RuleBasedTransliterator. More...

 RuleBasedTransliterator (const UnicodeString& ID, const UnicodeString& rules, UTransDirection direction, UnicodeFilter* adoptedFilter, UParseError& parseError, UErrorCode& status)
Constructs a new transliterator from the given rules. More...

 RuleBasedTransliterator (const UnicodeString& ID, const UnicodeString& rules, UTransDirection direction, UnicodeFilter* adoptedFilter, UErrorCode& status)
Constructs a new transliterator from the given rules. More...

 RuleBasedTransliterator (const UnicodeString& ID, const UnicodeString& rules, UTransDirection direction, UErrorCode& status)
Covenience constructor with no filter. More...

 RuleBasedTransliterator (const UnicodeString& ID, const UnicodeString& rules, UErrorCode& status)
Covenience constructor with no filter and FORWARD direction. More...

 RuleBasedTransliterator (const UnicodeString& ID, const UnicodeString& rules, UnicodeFilter* adoptedFilter, UErrorCode& status)
Covenience constructor with FORWARD direction. More...

 RuleBasedTransliterator (const UnicodeString& ID, const TransliterationRuleData* theData, UnicodeFilter* adoptedFilter = 0)
Covenience constructor. More...

 RuleBasedTransliterator (const RuleBasedTransliterator&)
Copy constructor. More...

virtual ~RuleBasedTransliterator ()
Transliteratorclone (void) const
Implement Transliterator API. More...

virtual void handleTransliterate (Replaceable& text, UTransPosition& offsets, UBool isIncremental) const
Implements. More...


Detailed Description

RuleBasedTransliterator is a transliterator that reads a set of rules in order to determine how to perform translations.

Rule sets are stored in resource bundles indexed by name. Rules within a rule set are separated by semicolons (';'). To include a literal semicolon, prefix it with a backslash ('\'). Whitespace, as defined by Character.isWhitespace(), is ignored. If the first non-blank character on a line is '#', the entire line is ignored as a comment.

Each set of rules consists of two groups, one forward, and one reverse. This is a convention that is not enforced; rules for one direction may be omitted, with the result that translations in that direction will not modify the source text. In addition, bidirectional forward-reverse rules may be specified for symmetrical transformations.

Rule syntax

Rule statements take one of the following forms:

$alefmadda=\u0622;
Variable definition. The name on the left is assigned the text on the right. In this example, after this statement, instances of the left hand name, "$alefmadda", will be replaced by the Unicode character U+0622. Variable names must begin with a letter and consist only of letters, digits, and underscores. Case is significant. Duplicate names cause an exception to be thrown, that is, variables cannot be redefined. The right hand side may contain well-formed text of any length, including no text at all ("$empty=;"). The right hand side may contain embedded UnicodeSet patterns, for example, "$softvowel=[eiyEIY]".
ai>$alefmadda;
Forward translation rule. This rule states that the string on the left will be changed to the string on the right when performing forward transliteration.
ai<$alefmadda;
Reverse translation rule. This rule states that the string on the right will be changed to the string on the left when performing reverse transliteration.

ai<>$alefmadda;
Bidirectional translation rule. This rule states that the string on the right will be changed to the string on the left when performing forward transliteration, and vice versa when performing reverse transliteration.

Translation rules consist of a match pattern and an output string. The match pattern consists of literal characters, optionally preceded by context, and optionally followed by context. Context characters, like literal pattern characters, must be matched in the text being transliterated. However, unlike literal pattern characters, they are not replaced by the output text. For example, the pattern "abc{def}" indicates the characters "def" must be preceded by "abc" for a successful match. If there is a successful match, "def" will be replaced, but not "abc". The final '}' is optional, so "abc{def" is equivalent to "abc{def}". Another example is "{123}456" (or "123}456") in which the literal pattern "123" must be followed by "456".

The output string of a forward or reverse rule consists of characters to replace the literal pattern characters. If the output string contains the character '|', this is taken to indicate the location of the cursor after replacement. The cursor is the point in the text at which the next replacement, if any, will be applied. The cursor is usually placed within the replacement text; however, it can actually be placed into the precending or following context by using the special character '</code>'. Examples:

a {foo} z > | @ bar; # foo -> bar, move cursor before a
{foo} xyz > bar @|; foo -> bar, cursor between y and z

UnicodeSet

UnicodeSet patterns may appear anywhere that makes sense. They may appear in variable definitions. Contrariwise, UnicodeSet patterns may themselves contain variable references, such as "$a=[a-z];$not_a=[^$a]", or "$range=a-z;$ll=[$range]".

UnicodeSet patterns may also be embedded directly into rule strings. Thus, the following two rules are equivalent:

$vowel=[aeiou]; $vowel>'*'; # One way to do this
[aeiou]>'*'; # Another way

See UnicodeSet for more documentation and examples.

Segments

Segments of the input string can be matched and copied to the output string. This makes certain sets of rules simpler and more general, and makes reordering possible. For example:

([a-z]) > $1 $1; # double lowercase letters
([:Lu:]) ([:Ll:]) > $2 $1; # reverse order of Lu-Ll pairs

The segment of the input string to be copied is delimited by "(" and ")". Up to nine segments may be defined. Segments may not overlap. In the output string, "$1" through "$9" represent the input string segments, in left-to-right order of definition.

Example

The following example rules illustrate many of the features of the rule language.

Rule 1. abc{def}>x|y
Rule 2. xyz>r
Rule 3. yz>q

Applying these rules to the string "adefabcdefz" yields the following results:

|adefabcdefz Initial state, no rules match. Advance cursor.
a|defabcdefz Still no match. Rule 1 does not match because the preceding context is not present.
ad|efabcdefz Still no match. Keep advancing until there is a match...
ade|fabcdefz ...
adef|abcdefz ...
adefa|bcdefz ...
adefab|cdefz ...
adefabc|defz Rule 1 matches; replace "def" with "xy" and back up the cursor to before the 'y'.
adefabcx|yz Although "xyz" is present, rule 2 does not match because the cursor is before the 'y', not before the 'x'. Rule 3 does match. Replace "yz" with "q".
adefabcxq| The cursor is at the end; transliteration is complete.

The order of rules is significant. If multiple rules may match at some point, the first matching rule is applied.

Forward and reverse rules may have an empty output string. Otherwise, an empty left or right hand side of any statement is a syntax error.

Single quotes are used to quote any character other than a digit or letter. To specify a single quote itself, inside or outside of quotes, use two single quotes in a row. For example, the rule "'>'>o''clock" changes the string ">" to the string "o'clock".

Notes

While a RuleBasedTransliterator is being built, it checks that the rules are added in proper order. For example, if the rule "a>x" is followed by the rule "ab>y", then the second rule will throw an exception. The reason is that the second rule can never be triggered, since the first rule always matches anything it matches. In other words, the first rule masks the second rule.

Author(s):
Alan Liu
Draft:

Definition at line 254 of file rbt.h.


Enumeration Value Documentation

RuleBasedTransliterator::PARSE_ERROR_BASE

RuleBasedTransliterator::BAD_VARIABLE_DEFINITION

RuleBasedTransliterator::MALFORMED_RULE

RuleBasedTransliterator::MALFORMED_SET

RuleBasedTransliterator::MALFORMED_SYMBOL_REFERENCE

RuleBasedTransliterator::MALFORMED_UNICODE_ESCAPE

RuleBasedTransliterator::MALFORMED_VARIABLE_DEFINITION

RuleBasedTransliterator::MALFORMED_VARIABLE_REFERENCE

RuleBasedTransliterator::MISMATCHED_SEGMENT_DELIMITERS

RuleBasedTransliterator::MISPLACED_CURSOR_OFFSET

RuleBasedTransliterator::MISSING_OPERATOR

RuleBasedTransliterator::MISSING_SEGMENT_CLOSE

RuleBasedTransliterator::MULTIPLE_ANTE_CONTEXTS

RuleBasedTransliterator::MULTIPLE_CURSORS

RuleBasedTransliterator::MULTIPLE_POST_CONTEXTS

RuleBasedTransliterator::TRAILING_BACKSLASH

RuleBasedTransliterator::UNDEFINED_SEGMENT_REFERENCE

RuleBasedTransliterator::UNDEFINED_VARIABLE

RuleBasedTransliterator::UNQUOTED_SPECIAL

RuleBasedTransliterator::UNTERMINATED_QUOTE


Member Function Documentation

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const UnicodeString & rules, UTransDirection direction, UnicodeFilter * adoptedFilter, UParseError & parseError, UErrorCode & status) [inline]

Constructs a new transliterator from the given rules.

Parameters:
rules   rules, separated by ';'
direction   either FORWARD or REVERSE.
Exceptions:
IllegalArgumentException   if rules are malformed or direction is invalid.
Draft:

Definition at line 394 of file rbt.h.

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const UnicodeString & rules, UTransDirection direction, UnicodeFilter * adoptedFilter, UErrorCode & status) [inline]

Constructs a new transliterator from the given rules.

Parameters:
rules   rules, separated by ';'
direction   either FORWARD or REVERSE.
Exceptions:
IllegalArgumentException   if rules are malformed or direction is invalid.

Definition at line 412 of file rbt.h.

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const UnicodeString & rules, UTransDirection direction, UErrorCode & status) [inline]

Covenience constructor with no filter.

Draft:

Definition at line 425 of file rbt.h.

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const UnicodeString & rules, UErrorCode & status) [inline]

Covenience constructor with no filter and FORWARD direction.

Draft:

Definition at line 437 of file rbt.h.

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const UnicodeString & rules, UnicodeFilter * adoptedFilter, UErrorCode & status) [inline]

Covenience constructor with FORWARD direction.

Draft:

Definition at line 448 of file rbt.h.

RuleBasedTransliterator::RuleBasedTransliterator (const UnicodeString & ID, const TransliterationRuleData * theData, UnicodeFilter * adoptedFilter = 0)

Covenience constructor.

Draft:

RuleBasedTransliterator::RuleBasedTransliterator (const RuleBasedTransliterator &)

Copy constructor.

Draft:

virtual RuleBasedTransliterator::~RuleBasedTransliterator () [virtual]

Transliterator * RuleBasedTransliterator::clone (void) const [virtual]

Implement Transliterator API.

Draft:

Reimplemented from Transliterator.

virtual void RuleBasedTransliterator::handleTransliterate (Replaceable & text, UTransPosition & offsets, UBool isIncremental) const [virtual]

Implements.

Transliterator#handleTransliterate.

Draft:

Reimplemented from Transliterator.


The documentation for this class was generated from the following file:
Generated at Wed Aug 16 16:05:49 2000 for ICU1.6 by doxygen 1.0.0 written by Dimitri van Heesch, © 1997-1999