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Add base direction as a fourth element of literals. #48

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Oct 13, 2023
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Add base direction as a fourth element of literals. #48

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2e96714
Add **text direction** as a forth element of literals.
gkellogg Jun 19, 2023
19a6413
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gkellogg Jun 20, 2023
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gkellogg Jun 21, 2023
9e0c5e7
Cleanup from changing "text direction" to "base direction".
gkellogg Jun 21, 2023
cdc41ec
Change "base text direction" to "base direction", as originally inten…
gkellogg Jun 22, 2023
ca650be
Define "directional language-tagged string".
gkellogg Jun 27, 2023
85b2a1d
Update spec/index.html
gkellogg Jun 27, 2023
7b17a8f
Suggestions from pchampin
gkellogg Jul 21, 2023
33186a0
Indicate the a plain literal has no explicit base direction, in addit…
gkellogg Jul 22, 2023
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gkellogg Jul 24, 2023
c45d947
Remove suggestion to format language tags based on BCP47 rules and fo…
gkellogg Jul 27, 2023
0633807
Merge branch 'main' into text-direction
gkellogg Aug 30, 2023
a0ee47a
Merge branch 'main' into text-direction
gkellogg Aug 31, 2023
2d153ec
* Base direction discussion from @aphillips
gkellogg Sep 28, 2023
f1b884f
Use I18N-GLOSSARY instead of i18n-glossary.
gkellogg Oct 12, 2023
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gkellogg Oct 13, 2023
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133 changes: 90 additions & 43 deletions spec/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@
{ name: "Brian McBride" }
],

xref: ["i18n-glossary", "infra"],
xref: ["I18N-GLOSSARY", "INFRA"],
github: "https://github.com/w3c/rdf-concepts/",
group: "rdf-star",
doJsonLd: true,
Expand Down Expand Up @@ -67,7 +67,10 @@
</ul>

<p>RDF 1.2 introduces <a>quoted triples</a> as another kind of <a>RDF term</a>
which can be used as the <a>subject</a> or <a>object</a> of another <a>triple</a>.</p>
which can be used as the <a>subject</a> or <a>object</a> of another <a>triple</a>.
RDF 1.2 also introduces <a>directional language-tagged strings</a>,
which contain a <a>base direction</a> element that allows the
initial text direction to be specified for presentation by a user agent.</p>

<p>RDF 1.2 Concepts introduces key concepts and terminology for RDF 1.2, discusses
datatyping, and the handling of <a>fragment identifiers</a> in IRIs within
Expand Down Expand Up @@ -145,9 +148,10 @@ <h3>Resources and Statements</h3>
resource denoted by a literal is called its
<a>literal value</a>. Literals have
<a>datatypes</a> that define the range of possible
values, such as strings, numbers, and dates. Special kind of literals,
<a>language-tagged strings</a>, denote
plain-text strings in a natural language.</p>
values, such as strings, numbers, and dates. Special kinds of literals &mdash;
<a>language-tagged strings</a> and <a>directional language-tagged strings</a> &mdash;
respectively denote plain-text strings in a natural language, and plain-text
strings in a natural language including an initial text direction.</p>

<p>Asserting an <a>RDF triple</a> says that <em>some relationship,
indicated by the <a>predicate</a>, holds between the
Expand Down Expand Up @@ -506,21 +510,21 @@ <h2>Strings in RDF</h2>
Within this, and related specifications, the term <dfn id="dfn-rdf-string">string</dfn>,
or <a data-lt="string">RDF string</a>,
is used to describe an ordered sequence of zero or more
<a data-cite="i18n-glossary#dfn-code-point" class="lint-ignore">Unicode code points</a>
which are <a data-cite="i18n-glossary#dfn-scalar-value" class="lint-ignore">Unicode scalar values</a>.
<a data-cite="I18N-GLOSSARY#dfn-code-point" class="lint-ignore">Unicode code points</a>
which are <a data-cite="I18N-GLOSSARY#dfn-scalar-value" class="lint-ignore">Unicode scalar values</a>.
Unicode scalar values do not include the
<a data-cite="i18n-glossary#dfn-surrogate" class="lint-ignore">surrogate code points</a>.
<a data-cite="I18N-GLOSSARY#dfn-surrogate" class="lint-ignore">surrogate code points</a>.
Note that most <a>concrete RDF syntaxes</a> require the use
of the UTF-8 character encoding [[!RFC3629]],
and use the `\u0000` or `\U00000000` forms to express certain non-character values.
</p>

<p>A string is identical to another string if it consists of the same sequence of code points.
An implementation MAY determine string equality by comparing the
<a data-cite="i18n-glossary#dfn-code-unit">code units</a> of two strings
that use the same <a data-cite="i18n-glossary#dfn-character-encoding">Unicode character encoding</a>
<a data-cite="I18N-GLOSSARY#dfn-code-unit">code units</a> of two strings
that use the same <a data-cite="I18N-GLOSSARY#dfn-character-encoding">Unicode character encoding</a>
(UTF-8 or UTF-16) without decoding the string into a
<a data-cite="i18n-glossary#dfn-code-point" class="lint-ignore">Unicode code point</a> sequence.</p>
<a data-cite="I18N-GLOSSARY#dfn-code-point" class="lint-ignore">Unicode code point</a> sequence.</p>
</section>
</section>

Expand Down Expand Up @@ -615,7 +619,7 @@ <h3>IRIs</h3>

<p><dfn>IRI equality</dfn>:
Two IRIs are the same if and only if they consist of the same sequence of
<a data-cite="i18n-glossary#dfn-code-point" class="lint-ignore">Unicode code points</a>,
<a data-cite="I18N-GLOSSARY#dfn-code-point" class="lint-ignore">Unicode code points</a>,
as in Simple String Comparison in
<a data-cite="rfc3987#section-5.3.1">section 5.3.1</a> of [[!RFC3987]].
(This is done in the abstract syntax, so the IRIs are resolved
Expand Down Expand Up @@ -696,15 +700,15 @@ <h2>Literals</h2>

<p>Literals are used for values such as strings, numbers, and dates.</p>

<p>A <dfn data-local-lt="RDF literal">literal</dfn> in an <a>RDF graph</a> consists of two or three
elements:</p>
<p>A <dfn data-local-lt="RDF literal">literal</dfn> in an <a>RDF graph</a> consists of
two, three, or four elements:</p>

<ul>
<li>a <dfn>lexical form</dfn> consisting of a sequence of
<a data-cite="i18n-glossary#dfn-code-point" class="lint-ignore">Unicode code points</a> [[!UNICODE]]
which are <a data-cite="i18n-glossary#dfn-scalar-value">Unicode scalar values</a>,
<a data-cite="I18N-GLOSSARY#dfn-code-point" class="lint-ignore">Unicode code points</a> [[!UNICODE]]
which are <a data-cite="I18N-GLOSSARY#dfn-scalar-value">Unicode scalar values</a>,
and therefore do not contain
<a data-cite="i18n-glossary#dfn-surrogate" class="lint-ignore">Unicode surrogate code points</a>.</li>
<a data-cite="I18N-GLOSSARY#dfn-surrogate" class="lint-ignore">Unicode surrogate code points</a>.</li>
<li>a <dfn>datatype IRI</dfn>, being an <a>IRI</a>
identifying a datatype that determines how the lexical form maps
to a <a>literal value</a>, and</li>
Expand All @@ -714,32 +718,48 @@ <h2>Literals</h2>
language tag MUST be well-formed according to
<a data-cite="bcp47#section-2.2.9">section 2.2.9</a>
of [[!BCP47]].</li>
<li>if and only if the <a>datatype IRI</a> is
<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#dirLangString</code>,
a non-empty <a>language tag</a>
that MUST be well-formed according to <a data-cite="bcp47#section-2.2.9">section 2.2.9</a>
of [[!BCP47]].
and a <dfn>base direction</dfn> that MUST be either `ltr` or `rtl`.</li>
</ul>

<p>A literal is a <dfn>language-tagged string</dfn> if the third element
is present. Lexical representations of language tags MAY be converted
to lower case. The value space of language tags is always in lower
case.</p>
is present and the fourth element is not present.
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Lexical representations of language tags MAY be converted
to lower case.
The value of language tags is always treated as being in lower case.</p>

<p>A literal is a <dfn id="dfn-dir-lang-string">directional language-tagged string</dfn>
if both the third element and fourth elements are present.
The third element, the language tag, is treated identically as in a <a>language-tagged string</a>,
and the fourth element, <a>base direction</a>, MUST be either `ltr` or `rtl`, which MUST be in lower case.</p>

<p>Please note that concrete syntaxes MAY support
<dfn data-lt="simple literal" class="export">simple literals</dfn> consisting of only a
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<a>lexical form</a> without any <a>datatype IRI</a> or <a>language tag</a>.
<a>lexical form</a> without any <a>datatype IRI</a>, <a>language tag</a>, or <a>base direction</a>.
Simple literals are syntactic sugar for abstract syntax
<a>literals</a>
with the <a>datatype IRI</a>
<code>http://www.w3.org/2001/XMLSchema#string</code>
(which is commonly abbreviated as <code>xsd:string</code>).
Similarly, most concrete syntaxes represent
<a>language-tagged strings</a> without
the <a>datatype IRI</a> because it always equals
<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#langString</code> (<code>rdf:langString</code>).</p>
<a>language-tagged strings</a> and <a>directional language-tagged strings</a> without
the <a>datatype IRI</a> because it always equals either
<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#langString</code> (<code>rdf:langString</code>)
or <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#dirLangString</code> (<code>rdf:dirLangString</code>), respectively.</p>

<p>The <dfn>literal value</dfn> associated with a <a>literal</a> is:</p>

<ol>
<li>If the literal is a <a>language-tagged string</a>,
then the literal value is a pair consisting of its <a>lexical form</a>
and its <a>language tag</a>, in that order.</li>
<li>if the literal is a <a>directional language-tagged string</a>, then the literal value is
a tuple of its <a>lexical form</a>, its <a>language tag</a>, and its <a>base direction</a>,
likewise in that order.</li>

<li>If the literal's <a>datatype IRI</a> is in the set of
<a>recognized datatype IRIs</a>, let <var>d</var> be the
Expand All @@ -762,14 +782,17 @@ <h2>Literals</h2>
not defined by this specification.</li>
</ol>

<p><dfn data-local-lt="term-equal">Literal term equality</dfn>: Two literals are term-equal (the same
RDF literal) if and only if the two <a>lexical forms</a>,
the two <a>datatype IRIs</a>, and the two
<a>language tags</a> (if any) compare equal,
using <a data-cite="i18n-glossary#dfn-case-sensitive">case sensitive matching</a>
<p><dfn data-local-lt="term-equal">Literal term equality</dfn>:
Two literals are term-equal (the same <a>RDF literal</a>)
if and only if the two <a>lexical forms</a>,
the two <a>datatype IRIs</a>,
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the two <a>language tags</a> (if any), and
the two <a>base directions</a> (if any) compare equal,
using <a data-cite="I18N-GLOSSARY#dfn-case-sensitive">case sensitive matching</a>
(see description of string comparison in <a href="#rdf-strings" class="sectionRef"></a>).
Thus, two literals can have the same value
without being the same RDF term. For example:</p>
without being the same <a>RDF term</a>.
For example:</p>

<pre>
"1"^^xs:integer
Expand All @@ -779,7 +802,27 @@ <h2>Literals</h2>
<p>denote the same <a data-lt="literal value">value</a>, but are not the
same literal <a>RDF terms</a> and are not
<a>term-equal</a> because their
<a>lexical form</a> differs.</p>
<a>lexical forms</a> differ.</p>
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<section id="section-text-direction" class="informative">
<h3>Initial Text Direction</h3>

<p>The <a>base direction</a> of a <a>directional language-tagged string</a>
provides a means of establishing the initial direction of text,
including text which is a mixture of right-to-left and left-to-right scripts.
The [[[?UAX9]]] [[?UAX9]] provides support for automatically rendering
a sequence of characters in logical order,
so that they are visually ordered as expected,
but this is not sufficient to correctly render bidirectional text.</p>

<p>For example, some text with a language tag "`he`" might be displayed
in a left-to-right context (such as an English web page) as
<bdi dir="ltr">פעילות הבינאום, W3C</bdi>, which is incorrect. When provided
to a user agent including base direction information (such as using
HTML's `dir` attribute) it can then be correctly presented as:
</p>
<div lang="he" dir="rtl">פעילות הבינאום, W3C</div>
</section>
</section>

<section id="section-blank-nodes">
Expand Down Expand Up @@ -1591,17 +1634,18 @@ <h2>Security Considerations</h2>

<section id="internationalization" class="appendix informative">
<h2>Internationalization Considerations</h2>
<p>RDF is restricted to representing Unicode <a>string</a> [[UNICODE]] values with left-to-right or right-to-left direction indicators.
RDF provides a mechanism for specifying the language associated with
a string (<a>language-tagged string</a>),
but does not provide a means of indicating the base direction of the string.</p>

<p>Unicode [[UNICODE]] provides a mechanism for signaling direction within a string
(see [[[UAX9]]] [[UAX9]]),
however, when a string has an overall base direction which cannot be determined by the
beginning of the string, an external indicator is required,
such as the [[HTML]] <a data-cite="HTML/dom.html#the-dir-attribute">dir attribute</a>,
which currently has no counterpart for <a>RDF literals</a>.</p>
(see [[[UAX9]]] [[UAX9]]).
RDF provides a mechanism for specifying the <a>base direction</a>
of a <a>directional language-tagged string</a>
to signal the initial text direction of a string.
For most human language strings, but particularly for those
whose base direction cannot be accurately determined from the
string content, is it valuable to have an external indicator in order
to get the proper display and isolation of the value.
One example of such an indicator is
the [[HTML]] <a data-cite="HTML/dom.html#the-dir-attribute">dir attribute</a>.
see [[STRING-META]].</p>

<p>[[[JSON-LD11]]] [[JSON-LD11]] introduced the
<a data-cite="JSON-LD11#the-i18n-namespace">i18n namespace</a> to use
Expand Down Expand Up @@ -1744,21 +1788,24 @@ <h2>Changes between RDF 1.1 and RDF 1.2</h2>
for informative definition of a <a>quad</a>.</li>
<li>Added <a href="#section-quoted-triples" class="sectionRef"></a>
and definitions for <a>quoted triple</a> and <a>asserted triple</a>.</li>
<li>Added the <a>base direction</a> element as part of
a <a>literal</a>,
and a description of its use in <a href="#section-text-direction" class="sectionRef"></a>.</li>
<li>Improved the use of IRI terminology,
and added <a href="#iri-abnf" class="sectionRef"></a>.
This improves the language using <a>relative IRI references</a>
and clarifies that, in the abstract syntax, IRIs are resolved,
avoiding the incorrect use of "absolute IRI".</li>
<li>Changed reference from DOM4, which was not a recommendation at the time, to [[DOM]],
making the <a>rdf:HTML</a> and <a>rdf:XMLLiteral</a> datatypes normative.</li>
making the definitions of <a>rdf:HTML</a> and <a>rdf:XMLLiteral</a> datatypes normative.</li>
<li>Added <a href="#section-additional-datatypes" class="sectionRef"></a>
and moved the sections about the <a>rdf:HTML</a> and <a>rdf:XMLLiteral</a>
datatypes to this appendix.</li>
<li>Added the <a>rdf:JSON</a> datatype, the definition of which is adopted
from <a data-cite="?JSON-LD11#the-rdf-json-datatype">Section&nbsp;10.2 The `rdf:JSON` Datatype</a>
in [[?JSON-LD11]].</li>
<li>Clarify Unicode terminology,
using <a data-cite="i18n-glossary#dfn-code-point" class="lint-ignore">Unicode code points</a>,
using <a data-cite="I18N-GLOSSARY#dfn-code-point" class="lint-ignore">Unicode code points</a>,
and restriction to the XML <a data-cite="XML11#charsets">Char</a> production.
Also removes obsolete recommendations for the use of Normalization Form C in literals.
Adds a definition of <a>string</a> that can be used in other RDF documents.</li>
Expand Down