Root Zone Label Generation Rules for the Tamil Script

Overview

This file contains Label Generation Rules (LGR) for the Tamil script for the Root zone. For more details on this LGR and its development, as well as background on the script, see "Proposal for a Tamil Script Root Zone Label Generation Rule-Set (LGR)" [Proposal-Tamil]. This file is one of a set of LGR files that together form an integrated LGR for the DNS Root Zone [RZ-LGR-4]. The format of this file follows [RFC 7940].

Repertoire

According to Section 5, "Repertoire" in [Proposal-Tamil] the Tamil LGR contains 48 single code points and 4 sequences. This LGR caters to the Tamil language written using Tamil script.

The repertoire is based on [MSR-4], which is a subset of [Unicode 6.3].

As part of the Root Zone, this LGR includes neither digits nor the HYPHEN-MINUS.

Code points outside the Tamil script that are listed in this file are targets for out-of-script variants and are identified by a reflexive (identity) variant of type "out-of-repertoire-var". They do not form part of the repertoire.

Each code point is tagged with the script or scripts that the code point is used with, one or more tag values denoting character category, and one or more references documenting sufficient justification for inclusion in the repertoire; see "References" below. Comments provide alternate names for some code points.

Variants

According to Section 6, "Variants", in [Proposal-Tamil], this LGR defines four sequences as in-script variants. Two of them are variants to single code points; the other two are variants of each other; all defined variants look exactly alike and can cause confusion even to a careful observer.

In addition to these, this LGR defines 6 cross-script variants with the Malayalam script.

Variant Disposition: Except as noted, variants are of type "blocked", making labels that differ only by these variants mutually exclusive: whichever label containing either of these variants is chosen earlier would be delegated, while any other equivalent label should be blocked.

For historical reasons, there are two sequences that both represent the same akshar (Shri) with exactly the same rendered form. These two sequences are thus semantically identical and users may choose either one, except that a single label must use one of these forms consistently. This variant pair is thus being defined as "allocatable" variant. (For more details see Section 6.1 in [Proposal-Tamil].)

The specification of variants in the Root Zone LGR follows the guidelines in [RFC 8228].

Character Classes

Tamil is an alphasyllabary and the heart of the writing system is the Akshar. This is the unit which is instinctively recognized by users of the script. The writing system of Tamil could be summed up as composed of Consonants, the Implicit Vowel Killer: Halant, Vowels and Visarga/Aytham.

Consonants: More details in Section 3.3.1, "The Consonants" in [Proposal-Tamil].

Halant / Virama: All consonants contain an implicit vowel /a/. A special sign is needed to denote that this implicit vowel is stripped off. This is known as the Pulli and encoded as U+0BCD ( ் ) TAMIL SIGN VIRAMA. The virama thus joins two adjacent consonants. In Tamil, there are only two cases where this forms conjuncts. More details in Section 3.3.2, "Virama/Pulli" of the [Proposal-Tamil].

Vowels and Matras: Separate symbols exist for all Vowels that are pronounced independently either at the beginning or after another vowel sound. To indicate a Vowel sound other than the implicit one following a consonant, a Vowel sign (matra) is attached to the consonant. Since the consonant has a built-in /a/, there are equivalent Matras for all vowels excepting the அ. More details in Section 3.3.3, "Vowels" in [Proposal-Tamil].

Visarga: The Visarga (or Aytham) is used in Tamil to represent a sound very close to /ḵ/. More details in Section 3.3.4, "Visarga/Aytham" in [Proposal-Tamil].

Whole Label Evaluation (WLE) and Context Rules

Default Whole Label Evaluation Rules and Actions

The LGR includes the set of required default WLE rules and actions applicable to the Root Zone and defined in [MSR-4]. They are marked with ⍟. The default prohibition on leading combining marks is equivalent to ensuring that a label only starts with a consonant or vowel.

Tamil-specific Rules and Action

These rules have been drafted to ensure that the prospective Tamil label conforms to akshar formation norms as desired in Tamil script. These norms are exclusively presented as context rules.

The following symbols are used in the WLE rules:
C → Consonant
M → Matra
H → Haleant / Virama =Pulli
X → Visarga = Aytham

The rules are:

1. H: must be preceded by C
2. M: must be preceded by C
3. X: cannot be preceded by X

The following whole-label rule and associated action prevent the mixing of two allocatable variants of the same sequence within the same label. This reduces overproduction of variant labels.

4. Two representations of 'Shri' cannot be mixed in the same label

More details in Section 7, "Whole Label Evaluation Rules (WLE)" in [Proposal-Tamil].

Methodology and Contributors

The Root Zone LGR for the Tamil script was developed by the Neo-Brahmi Generation Panel (NBGP) the members of which have experience in linguistics and computational linguistics in a wide variety of languages written with Neo-Brahmi scripts. Under the Neo-Brahmi Generation Panel, there are nine scripts belonging to separate Unicode blocks. Each of these scripts has been assigned a separate LGR, with the Neo-Brahmi GP ensuring that the fundamental philosophy behind building each LGR is in sync with all other Brahmi derived scripts. For further details on methodology and contributors, see Sections 4 and 8 in [Proposal-Tamil], as well as [RZ-LGR-4-Overview].

References

The following general references are cited in this document:

[MSR-4]

Integration Panel, "Maximal Starting Repertoire — MSR-4 Overview and Rationale", 7 February 2019,
https://www.icann.org/en/system/files/files/msr-4-overview-25jan19-en.pdf

[Proposal-Tamil]

Neo-Brahmi Generation Panel, "Proposal for a Tamil Script Root Zone Label Generation Rule-Set (LGR)", 6 March 2019,
https://www.icann.org/en/system/files/files/proposal-tamil-lgr-06mar19-en.pdf

[RFC 7940]

Davies, K. and A. Freytag, "Representing Label Generation Rulesets Using XML", RFC 7940, August 2016,
http://www.rfc-editor.org/info/rfc7940

[RFC 8228]

A. Freytag, "Guidance on Designing Label Generation Rulesets (LGRs) Supporting Variant Labels", RFC 8228, August 2017,
https://www.rfc-editor.org/info/rfc8228

[RZ-LGR-4-Overview]

Integration Panel, "Root Zone Label Generation Rules - LGR-4: Overview and Summary", 05 November 2020 (PDF),
https://www.icann.org/sites/default/files/lgr/lgr-4-overview-05nov20-en.pdf

[RZ-LGR-4]

Integration Panel, "Label Generation Rules for the Root Zone — LGR-4", 05 November 2020 (XML),
https://www.icann.org/sites/default/files/lgr/lgr-4-common-05nov20-en.xml
non-normative HTML presentation:
https://www.icann.org/sites/default/files/lgr/lgr-4-common-05nov20-en.html

[Unicode 6.3]

The Unicode Consortium. The Unicode Standard, Version 6.3.0, (Mountain View, CA: The Unicode Consortium, 2013. ISBN 978-1-936213-08-5)
http://www.unicode.org/versions/Unicode6.3.0/

For references consulted particularly in designing the repertoire for the Tamil script for the Root Zone please see details in the Table of References below. References [0] and [7] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. References [101] and above correspond to sources given in [Proposal-Tamil] justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values.

4.1 Character Classes

The following table lists all named and implicit classes with their definition and a list of their members intersected with the current repertoire (for larger classes, this list is elided).

4.2 Whole label evaluation and context rules

The following table lists all named rules defined in the LGR and indicates whether they are used as trigger in an action or as context (when or not-when) for a code point or variant.

4.3 Actions

The following table lists the actions that are used to assign dispositions to labels and variant labels based on the specified conditions. The order of actions defines their precedence: the first action triggered by a label is the one defining its disposition.