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Re: comments on the N3 team submission

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 16 Jan 2008 16:31:50 -0500 (EST)
Message-Id: <20080116.163150.64542786.pfps@research.bell-labs.com>
To: semantic-web@w3.org
From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Subject: comments on the N3 and Turtle team submissions
Date: Wed, 16 Jan 2008 09:08:22 -0500 (EST)

> From: Sandro Hawke <sandro@w3.org>
> Subject: Re: ISSUE-93 (Language tags): RFC 3066 - Tags for the Identification of Languages 
> Date: Wed, 16 Jan 2008 09:29:48 -0500

[...]

> > If you've actually read through the documents [the N3 and Turtle
> > team submissions], it'd be great if you'd
> > send along any constructive comments you have.
> > 
> >      - s
> 
> As I've said in some other contexts, I'm willing to provide what I
> consider to be constructive comments on many documents.  However I don't
> guarantee that the authors will like my comments.
> 
> peter


** My comments are on lines starting with **
** Typos or questionable wording are often signaled with [sic]

** Because I have many comments on the document, I decided to copy the
** document as text and put my comments in-line with the text.

** Summary:  This document is quite shoddily put together.  It has
** numerous typographical and grammatical errors.  Worse, there are very
** many undefined terms, which is quite astonishing in a document that
** "defines Notation 3".  Even worse, there is a systematic vagueness
** about the meaning of N3 - is the meaning of N3 a set of RDF triples,
** is the meaning of N3 some operational meaning, is the meaning of N3
** some logical meaning - at various times all of these are alluded to
** but no meaning is actually produced.

  Notation3 (N3): A readable RDF syntax

** What is N3?  If N3 is an RDF syntax, then its meaning should be given
** by a translation to RDF triples (or into the RDF model theory).  If
** not, then the title needs changing.

    W3C Team Submission 14 January 2008

This version:
    http://www.w3.org/TeamSubmission/2008/SUBM-n3-20080114/

Latest version:
    http://www.w3.org/TeamSubmission/n3/

Authors:
    Tim Berners-Lee </People/Berners-Lee/>, W3C
    Dan Connolly </People/Connolly/>, W3C

Copyright <http://www.w3.org/Consortium/Legal/ipr-notice#Copyright> ©
2008 W3C <http://www.w3.org/>^® (MIT <http://www.csail.mit.edu/>, ERCIM
<http://www.ercim.org/>, Keio <http://www.keio.ac.jp/>), All Rights
Reserved. W3C liability
<http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>,
trademark <http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>
and document use
<http://www.w3.org/Consortium/Legal/copyright-documents> rules apply.

------------------------------------------------------------------------


    Abstract

The Resource Description Framework (RDF) is a general-purpose language
for representing information in the Web.

This document defines /Notation 3/ (also known as /N3/), an assertion
and logic language which is a superset of RDF. N3 extends the RDF
datamodel by adding formulae (literals which are graphs themselves),
variables, logical implication, and functional predicates, as well as
providing an textual syntax alternative to RDF/XML.


    Status of This Document

/This section describes the status of this document at the time of its
publication. Other documents may supersede this document. A list of
current W3C publications can be found in the W3C technical reports index
<http://www.w3.org/TR/> at http://www.w3.org/TR/./


This January 2008 W3C Team Submission
<http://www.w3.org/TeamSubmission/>, with its linked grammars and test
suites, defines the N3 language. It is the product of experience with
working code since 2000, and much discusssion in secifically [sic] the W3C RDF
Interest Group and Semantic Web Interest Groups [sic]. It may be put into W3C
note form, or even Recommendation track form, in the future. There is a
large amount of implementation with N3 and its subsets. There [sic] also a
large number of tests. However, the test suite has not been completely
vaidated [sic] against the grammar.

By publishing this document, Tim Berners-Lee and Dan Connolly have made
a formal submission to W3C for discussion. Publication of this document
by W3C indicates no endorsement of its content by W3C, nor that W3C has,
is, or will be allocating any resources to the issues addressed by it.
This document is not the product of a chartered W3C group, but is
published as potential input to the W3C Process. Please consult the
complete list of acknowledged W3C Team Submissions <../../>.

------------------------------------------------------------------------


    Table of Contents

   1. Introduction <#intro>
   2. Grammar <#grammar>
         1. Encoding <#encoding>
         2. MIME type text/rdf+n3; charset=utf-8 <#mimetype>
               1. MIME parameter: charset <#charset>
               2. Fragment identifier syntax and semantics <#frag>
   3. Syntax details <#syntax>
         1. Whitespace <#whitespace>
         2. Base URI <#base>
               1. Example <#ex1>
         3. Namespaces <#namespaces>
         4. @keywords <#keywords>
         5. Strings <#strings>
         6. String escaping <#escaping>
   4. Semantics <#semantics>
         1. Shorthand for common predicates <#shorthand>
         2. Blank nodes <#bnodes>
               1. Underscore namespace <#underscore>
               2. Square bracket blank node syntax <#anonbnode>
               3. Paths <#path>
         3. Formulae <#Quoting>
               1. Example: <#ex2>
         4. Quantification <#Quantifica>
         5. Lists <#lists>
   5. Notes on Numbers <#numbers>
         1. Boolean literals <#booleans>
   6. Appendix: N3 Subsets <#subsets>
         1. Acknowledgements <#ack>


      Appendices

   1. Appendix: Change History <#chlog>
   2. References <#References>
         1. Normative <#ref-norm>
         2. Non-normative <#ref-inform>


    Introduction

This is the specification of the Notation3 language, of internet Media
Type text/rdf+n3. Normative parts of the specification are thus.
Non-normative parts and comments thus.

This is a language which is a compact and readable alternative to RDF's
XML syntax, but also is extended to allow greater expressiveness. It has
subsets, one of which is RDF 1.0 equivalent, and one of which is RDF
plus a form of RDF rules.

This document is a specification of the language suitable for those
familiar with the general concepts. The developer learning N3 is invited
to try the A tutorial </2000/10/swap/doc/Overview.html>, while
implementers looking for for a particular detail of the definition of
the logic are steered toward the operational semantics.
</DesignIssues/N3Logic> There is also a list of other N3 resources
</DesignIssues/N3Resources>.

This language has ben developed in the context of the Semantic Web
Interest Group. Comments on this document should be sent to
public-cwm-talk@w3.org

The aims of the language are

    * to optimize expression of data and logic in the same language,
    * to allow RDF to be expressed,
    * to allow rules to be integrated smoothly with RDF,
    * to allow quoting so that statements about statements can be made, and
    * to be as readable, natural, and symmetrical as possible.

The language achieves these with the following features:

    * URI abbreviation using prefixes which are bound to a namespace
      (using @prefix) a bit like in XML,
    * Repetition of another object for the same subject and predicate
      using a comma ","
    * Repetition of another predicate for the same subject using a
      semicolon ";"
    * Bnode syntax with a certain properties just put the properties
      between [ and ]
    * Formulae allowing N3 graphs to be quoted within N3 graphs using {
      and }
    * Variables and quantification to allow rules, etc to be expressed
    * A simple and consistent grammar.


    Grammar

The grammar of N3 is defined by a context free grammar:

    * Context-free grammar in N3 <../../../2000/10/swap/grammar/n3.n3>

While this obviously provides a bootstrap problem for implementers, it
is a common format one would expect N3 developers to share.
Non-authoritative generated copies of the same grammar are provided in
the following dialects:

N3 <../../../2000/10/swap/grammar/n3.n3> RDF/XML
<../../../2000/10/swap/grammar/n3.rdf>  EBNF as used in XML 1.1
<../../../2000/10/swap/grammar/n3-ietf.txt>  HTML
<../../../2000/10/swap/grammar/n3-report.html>  yacc
<../../../2000/10/swap/grammar/n3-selectors.n3-yacc.y>

** I'm going to use http://www.w3.org/2000/10/swap/grammar/n3-ietf.txt

** I note that this file appears to be missing parts of the productions,
** notably for existential and universal.
** I note the grammar allows 
** statement -> simpleStatement -> subject propertylist 
** -> expression void -> pathitem pathtail -> symbol void -> explicituri
** so a statement can be simply an explicituri
** I also note that statement can not generate a trailing .

      Test Suite

The N3 test suite provides a check for implementers.

    * Test suite space <http://www.w3.org/2000/10/swap/test/n3/>

The work of validating the grammar and test suite against each other is
not complete.


      Encoding

N3 files are encoded in UTF-8 (See RFC2279
<http://www.ietf.org/rfc/rfc2279.txt>), in [sic] normalized in Normalization
Form <http://www.unicode.org/unicode/reports/tr15/> C. The language is
defined in terms of a sequence of Unicode characters.

(Implementations may chose to implement using 8-bit bytes, passing bytes
>7F transparently, but this will not allow them to check the validity of
embedded non-ASCII characters. Note also that some systems internally
use UTF-16 encoding which uses 16 bits as a rule, but allows full 20-bit
unicode code points to be encoded as two 16-bit units. This may be a
suitable implementation for a system which passes such characters
without counting them or breaking apart strings of them. A full 32
unicode implementation would normally be preferable.)

The exact set of unicode character [sic] to be allowed in (a) literal strings
or (b) identifiers may need to be revised if the unicode specification
is revised in unanticipated ways in the future) [sic]


      MIME type text/n3; charset=utf-8

This document defines, in the linked grammar, the allowable syntax and,
for documents of valid syntax, the meaning, of a document in the
[proposed] |text/rdf+n3| MIME type (Internet Content Type). It also
defines the fragment identifier syntax and semantics.

** Which mime type is it text/n3 or text/rdf+n3?

As the type is in the text tree, agents which do not understand it will
and should display it as text for human consumption.


        MIME parameter: charset

This MIME type is used with a /charset/ parameter: the encoding is
always /utf-8./ The only occasion that the encoding can be omitted is
when it happens (and is guaranteed by the sender) that all of the
unicode characters in the file are in fact that subset which is the
7-bit ASCII set. This is because the default encoding for types in the
text/* tree is ASCII.


        Fragment identifier syntax and semantics

The fragment identifier part of a URI where the rest of the URI is that
of an information resource which has a representation in N3 is used to
identify any thing whatever, abstract or concrete.

The N3 representation may give information about that thing by including
its URI as one of the terms in a statement.

The fragment identifier syntax should match the syntax for the part of a
qname after the colon. The qname syntax can be used within the document
to refer to the thing the full URI identifies.

It is good practice to use URIs of this form to identify things, and to
ensure that the N3 document which is served to the inquirer contains
useful information which the publisher of the information, and owner of
the URI, considers relevant, useful and interesting to any agent (human
or machine) dereferencing the URI. It is good practice to include
statements relating the thing to other things, also identified by URIs.
The use of URIs whose part before the hash sign is a different
information resource constitutes a form of link, leading an agent to
possibly dereference the other URI and gain more information.


    Syntax details

This section describes the syntax which is not given by the grammar. 
** Huh?  Oh, perhaps you mean the part of the syntax that is not
** captured in the grammar.
If
a parser is generated automatically from the grammar, the tokenizer must
be written to take the following into account.


      Whitespace

Tokenizing and white space is not specified in the grammar for
simplicity. White space must be inserted whenever the following token
could start with a character which could extend the preceding token.
Whitespace may not be inserted within a token, except that it may be
freely added and removed whitespace within [sic] a URI between angle brackets.
This allows complex URIs to be broken onto several lines, which in turn
allows N3 to be sent for example of email systems in which a limited
line length.

All URIs are quoted with angle brackets. Whitespace within the <> is to
be ignored. Whitespace may therefore be used on output to split a long
URI between lines.
** Huh? Perhaps an accidental repetition?


      Base URI

The /*@base*/ directive 
** There are no directives in the grammar.
** I'm assuming you mean the @base" explicituri *declaration*
sets the base URI to be used for the parsing of
relative URIs. It takes, itself, a relative URI, so it can be used to
change the base URI relative to the previous one.


        Example

@base  <http://example.org/products/>.
...
@base  <prod123/>.
...
@base  <../>.

Note that if files are to be concatenated, the base URI of one may
adversely affect parsing of another, unless @base is avoided, or used
consistently with absolute URIs.


      Namespaces

The /*@prefix*/ directive 
** I'm assuming you mean the @prefix"  prefix explicituri *declaration*
** There are no directives in the grammar.
binds a prefix to a namespace URI. It
indicates that a qualified name (qname) with that prefix will thereafter
be a shorthand for a URI consisting of the concatenation of the
namespace identifier and the bit of the qname to the right of the (only
allowed) colon.

The namespace prefix may be empty, in which case the qname starts with a
colon. This is known as the default namespace. The empty prefix "" is by
default , bound to "#" -- the local namespace of the file. The parser
behaves as though there were a

@prefix : <#>.

just before the file. This means that |<#foo>| can be written |:foo| and
using |@keywords| one can reduce that to |foo|.


      @keywords

Keywords are a very limited set of alphanumeric strings which are in the
grammar prefixed by an at sign "@".

Qnames using the default namespace which has an empty prefix start with
a colon. The language becomes more readable when keywords and/or qnames
can be written without the at sign or colon prefix, but clearly one
cannot do both.

In many languages similar to N3, there is a risk of ambiguity as to
whether a naked alphanumeric string is a keyword or an identifier.
Serious version management problems occur when new keywords are added to
a language, changing things which were identifiers into keywords. N3 is
designed to be extended in the future, and possibly branched into
specific languages such as query languages. For this reason, an N3
document can declare which keywords it uses without the at sign. This
allows N3 to be extended without the danger that existing documents be
incorrectly interpreted by future systems, or future documents by
existing systems.

If no @keywords directive
** Not in grammar
is given, qualified names all have colons, and
unquoted alphanumerics are all keywords. Only the keywords |is|, |of|,
and |a| may be used naked.
** From the document: All URIs are quoted with angle brackets.
** The qname syntax can be used within the document to refer to the
** thing the full URI identifies. 
** Unquoted = naked, so I guess that this means that the only unquoted
** (i.e., without : or <>) strings are the above three.

If the *@keywords* directive
** Not in grammar
is given, the keywords given will
thereafter be recognized without a "@" prefix, and anything else is a
local name in the default namespace. Any keyword may still be given,
even if not in the keyword list, by prefixing it with "@". 
** Anything else?  Including things like "."?

Because
keywords are declared in this way, we will have the freedom later to
make extensions to the syntax using new keywords without fear of
ambiguity. However, the tokenizer has to be aware of the |@keywords|
setting. The grammar is written as without reference to the keywords
system at all, on the assumption that the string has been preprocessed
by a keyword processor to put a "@" on all keywords and a ":" on all
qnames in the default namespace.


      Strings

The """value""" string form is used simply for multi-line values or
values containing quote marks.

The Unicode sets have been defined to be compatible with those used in
XML 1.1. Unicode has changed over the years, and the intention of this
specification would be to change if necessary. However, it is understood
that the character ranges in the grammar should be stable even though
the introduction of a few new code points into the Unicode system.


      String escaping

Escaping in strings uses the same conventions as Python strings
<http://www.python.org/doc/current/ref/strings.html> except for a \U
extension introduced by NTriples spec. N3 strings represent ordered
sequences of Unicode characters.

Some escapes (\a, \b, \f, \v) should be avoided because the
corresponding characters are not allowed in RDF.

*Escape Sequence*   *Meaning* 
|\newline|  Ignored
|\\|  Backslash (|\|)
|\'|  Single quote (|'|)
|\"|  Double quote (|"|)
|\n|  ASCII Linefeed (LF)
|\r|  ASCII Carriage Return (CR)
|\t|  ASCII Horizontal Tab (TAB)
|\uhhhh|  character in BMP with Unicode value U+hhhh
|\U00hhhhhh|  character in plane 1-16 with Unicode value U+hhhhhh

In N3, the double quote character is used for strings. The single quote
character is reserved for future use. The single quote character does
not need to be escaped in an N3 string.

**RDF and N3 are defined in terms of characters, not bytes. Therefore,
the \ooo and \xhh escapes are not used.

The hexadecimal digit as in unicode escapes are UPPERCASE. This is
designed to match the NTriples strings </TR/rdf-testcases/#ntrip_strings>.


    Semantics

This section describes the meaning of the productions in the grammar

An N3 document encodes a set of statements, and its meaning is the
conjunction of the meaning of the statements.

The statement of the form |x p y.| 
** This is not a valid form for a statement!!!
** What are x p y?  Can they be anything?
asserts that the relation p holds
** No definition of asserts.
between x and y. The semantics of statements, where they are valid RDF
statements, are those described in the RDF abstract syntax document [RDFAS].
** RDFAS (http://www.w3.org/TR/rdf-concepts/) does not provide semantics
** for anything. 

When p is identified by a URI, 
** identified is undefined in this context
and that URI when dereferenced in the Web
gives some information, 
** "gives some information" is undefined
that information may in practice be used to
determine more information about the semantics of the statement.
** "determine more information" is undefined

In property lists, the semicolon /;/ is shorthand for repeating the
subject. In object lists /,/ is shorthand for repeating the verb.
** Where is the subject / verb repeated?


      Shorthand for common predicates

For three URIs commonly used as predicates, 
** predicate is not a grammar nonterminal
N3 provides a special
shorthand syntax. This may only be used in the predicate position in a
statement. The RDF type predicate shorthand is the keyword |a|. (This
needs no @ sign, unless @keyword is given and it is not in the keyword
list.)

Shorthand  stands for
|a|  |<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>|
|=|  |<http://www.w3.org/2002/07/owl#sameAs>|
|=>|  |<http://www.w3.org/2000/10/swap/log#implies>|
|<=|  |<http://www.w3.org/2000/10/swap/log#implies>| 
 but in the inverse direction
** inverse direction is undefined




      Blank nodes

There are several ways in N3 of representing a blank, or unnamed node:
** Different notion of represent from strings
** blank node not defined
the underscore namespace, the square bracket syntax, and the path syntax.
** This is not semantics - this is syntax.


        Underscore namespace

N3 allows has a special _: namespace prefix. An identifier of such a
form (e.g. |_:a17|) represents an [sic] blank node. The name a17 is only used
in the serialization to connect different mentionings of the same node.
** same node is not defined
There is no commitment to it as a name. It may not be used as a URI. A
serialization which uses arbitrary different node identifiers is
completely equivalent, 
** equivalent is undefined
as is one which uses the other blank node
syntaxes below for the same data.

When formulae are nested, _: blank nodes syntax [sic] used to only identify
blank node [sic] in the formula it occurs directly in. It [sic] is an arbitrary
temporary name for a symbol which is existentially quantified 
** existentially quantified undefined in this context
within the
current formula (not the whole file). They can only be used within a
single formula, and not within nested formulae.
** blank nodes cannot occur in nested formulae at all?

This is the one blank node syntax available even in the NTriples minimal
subset of N3.


        Square bracket blank node syntax

|[ pl ]| means /x/, where there exists some /x/ 
** exists not defined in this context
such that x has
properties in the property list |pl|. For example,

|[ :firstname "Ora" ] dc:wrote [ dc:title "Moby Dick" ] .|

is a statement which would be means in math
** Logic, not math, but which logic?

exists x, y . firstname(x, "Ora") & dc:wrote(x,y) & dc:title (y, "Moby
Dick")

or in english "Some person who has a first name Ora wrote a book
entitled "Moby Dick". Note *not* "/the/ book" or "/the/ person".

This can equally well be written

[x:firstname "Ora" ; dc:wrote [dc:title "Moby Dick" ]] .

or

[] x:firstname "Ora" ; dc:wrote [dc:title "Moby Dick" ].

** Are these syntactically the same?

The [] maybe read loosely as "something".


        Paths

These are just shorthand. /x/!/p/ means [ is /p/ of /x/ ] in the above
anonymous node notation. You can read it as "x's p". This is a little
reminiscent of the "." in object oriented programming "object.slot" syntax.
** What about issues related to existence or uniqueness?

The reverse traversal, /x/^/p/ means [ /p/ /x/ ] . For either forward or
backward traversal, /p/ is a property, and /x/ can be a whole path with
both ! and ^ in it.

/Example:/

|:joe!fam:mother!loc:office!loc:zip| Joe's mother's office's zipcode

|:joe!fam:mother^fam:mother| Anyone whose mother is Joe's mother.


      Formulae

An RDF document parses to a set of statements, or [sic] graph. However RDF
itelf has no datatype allowing a graph as a literal value. N3 extends
RDF allows [sic] a graph itself to be referred to within the language, where
it is known as a formula. A { statementlist } is a formula whose meaning
is the the logical conjunction (equivalent to syntactic juxtaposition)
** syntactic juxtaposition may not be equivalent to logical conjunction
of the statements in the list. 
** statementlist may not expand to a sequence of statements
It is a set, as the same statement
occuring more than once has no meaning. It is [sic] unordered set.
** I don't know what an ordered set would be.


        Example:

{ [ x:firstname  "Ora" ] dc:wrote [ dc:title  "Moby Dick" ] } a n3:falsehood .

This claims that the expression in {braces} is false
** No notion of truth or falsity yet.
 - that there is
nothing called Ora which wrote anything titled "Moby Dick".
** What about quantifier scoping?

A formula is considered, like a literal string, to be defined only by
its contents.
** This is generally not true.  The meaning of formulae in many logics
** depends on a context, for example, consider free variables.

      Quantification

Apart from the set of statements, a formula also has a set of URIs of
symbols which are universally quantified, and a set of URIs of symbols
which are existentially quanitified. 
** A formula contains only a statement list at the top level, which
** doesn't have a place for quantification.  Where then does this come
** from?
Variables are then in general
symbols which have been quantified. 
** What is quantification here?  How are symbols quantified?
There is a also a shorthand syntax
?x which is the same as :x except that it implies that x is universally
quantified not in the formula but in its parent formula[sic]
** What if there is no parent formula?

The semantics of a formula are than [sic] the contents are quoted. 
** The only notion of quoting so far is quoting URIs.
Variable substitution
** Variable substitution is not defined
 *does* recursively take place within a formula, but
substitution of equals 
** substitution of equals  is not defined
does *not*. The variable substitution is used for
example when formulae are used for rules, and patch file formats. See
the tutorial introduction </2000/10/swap/doc/Rules> to rules.

Certain propoerties may, by their semantics, 
** How is this semantics specified?
allow the propagataion of
substitution of equals, by agents which are aware of that semantics. So
for example, if the statement { F ex:or G } is true, where F and G are
formulae, then it ise [sic] useful to define a disjunction operator ex:or such
that if a = b, then it is also true that { F ex:or G' } where G' is the
result or [sic] substituiting [sic] b for a in G.
** How is this to be done?

The |@forAll| directives 
** not in grammar
declare variables which are universally
quantified: the formula is true for any value of the variable.
** What formula?  
** Value of variable not defined
Similarly, |@forSome| 
** not in grammar
gives an existential quantification: there exists
some value of the variable
** Value of variable not defined
 for which the formula is true.
** truth of formula not defined
(Note also
that the blank node notations above all introduce introduce a blank
node, which is an unnamed existential variable)

@forSome <#g>. <#g> <#loves> <#you>

is equivalent to

[ <#loves> <#you> ] .

** Equivalence is not defined

If both universal and existential quantification are specified for the
same formula, 
** How is this done?
then the scope of the universal quantification is outside
the scope of the existentials:

@forAll <#h>. @forSome <#g>. <#g> <#loves> <#h> .

means

for all h
   for some g
     g loves h

("Every has someone who loves them" rather than "Somebody loves everybody")

which you might think of as

∀h(∃g(loves(g,h))


      Lists

Notation3 in practice uses lists frequently,
** lists not in grammar
as ordered containers, as
argument lists to Nary functions, and so on. Implementations may treat
/list/ as a data type rather than just a ladder of rdf:first and
rdf:rest properties. The use of rdf:first and rdf:rest can be regarded
as a reification of the list datatype.
** reification not defined
This use of lists requires more axioms than are actually defined in the
RDF specification.
** Where in the RDF specification?

   1. All lists exist. 
** All lists not defined
** exist not defined
      The statement [rdf:first <a>; rdf:rest rdf:nil].
** Strangely enough, this *is* a statement in the grammar.
      carries no information in that the list ( ,a> ) [sic] exists and this
      expression carries no new information about it.
   2. A list has only one rdf:first. 
** Not defined.
      rdf:first is functional. 
** Not defined
      If the
      same thing has rdf:first arcs [sic] from it, they must be to nodes which
      are RDF equivalent
** RDF equivalence is defined on graphs, not nodes.
      - are the same RDF node.
** No notion in RDF of nodes being the same.

   3. Lists are the same RDF node if they have the same the:first [sic] and
      the same rdf:rest.
** No notion in RDF of nodes being the same.

This may seem obvious when you think of a list as a datatype.
Occasionally people express surprise that statements like the one above
which have a list as a subject but no information about it disappear
when loaded into an N3 store.


    Notes on Numbers

The BNF syntax above describes the syntax for various literal
productions. These syntax strings identify values which are members of
various classes of number. 
** Which classes?
The BNF productions should not be confused
with the relationship between number classes. In the syntax, integer,
rational and real productions are distinct. 
** No productions for rational or real in the grammar.
When it comes to the values
they represent, 
all integers are also rational numbers, and all
nationals [sic] are also real numbers.

There is no distinction between the rationals 1.0 
** 1.0 is in the language of decimal and double
and 1/1 
** 1/1 is not in the language at all, except, perhaps, as a naked keyword or identifier
and the the [sic]
integer 1. The semantics of rational numbers are true to normal
mathematical equality.
** As opposed to abnormal mathematical equality?

The issue of reals is more complicated, as any real literal is necessary
approximate. 
** Not so.  A treatment of real numbers would have "1.0"^^real be an
** exact real number.
So while there is a real number which is equal to the
rationals 1 or 1/3, reals do not support this comparison. 
** What comparison?
(See XML
Schema Datatypes)


      Boolean literals

The words |true| and |false| are boolean literals.
@@ keywords?


    Appendix: N3 Subsets

For various purposes it is useful to define limited subsets of the
language. These are defined in terms of N3 by grammar.

NTriples </TR/rdf-testcases/#ntriples> is an /extremely/ constrained
language which uses hardly any syntactic sugar at all: it is optimized
for reading by scripts, and comparing using text tools. It just allows
one triple on each line. It was designed for the RDF test suite parser
reference output.

[The RDF test suite format is not committed to be an exact subset of N3,
and currently (2004) specified uses a \uXXXX form for encoding unicode
characters in URIs, in variance with N3, and the IRI drafts which use
%XX encoding of utf-8. Currently this output option is a --n3=u flag in
cwm].

Turtle <http://www.dajobe.org/2004/01/turtle/> is another subset, for
only expressing RDF. It is like n3-rdf below except that it does not
have the path syntax. It is a subejct [sic] of a searate [sic] document.

The fact that the turtle language is a subset of the N3 language has not
been checked from the grammars.

Grammars for N3 subsets are linked below.

BNF grammar descriptions of N3 N3 the full language  N3
</2000/10/swap/grammar/n3.n3>  RDF/XML  HTML
</2000/10/swap/grammar/n3-report.html>  yacc
</2000/10/swap/grammar/n3-selectors.n3-yacc.y>

N3-rdf (under development). This is an N3 language which is constrained
so that only correct RDF graphs can be defined. This is all you need for
data.  N3 </2000/10/swap/grammar/n3-rdf.n3>  RDF/XML  HTML
</2000/10/swap/grammar/n3rdf-report.html>  

N3-rules (under development). This subset allows {} only for making
rules like {...} =>{...}, to be equivalent to various other rule
languages out there.  N3 </2000/10/swap/grammar/n3-rules.n3>  RDF/XML
HTML </2000/10/swap/grammar/n3rules-report.html>  

N3-QL </DesignIssues/N3QL.html> (under development) Restrictions very
similar to N3-Rules  N3    

Comparison of N3 subsets /Feature/  Expresses RDF 1.0  @prefix

[], ; a

 Collections  Numeric literals  Literal subj  RDF Path  Rules  Formulae
/syntax/:    (<a> <b>)  2  7 a n:prime.  x!y^z  {?x}=>{?x}  {} @forAll
NTriples  y        
Turtle <http://www.dajobe.org/2004/01/turtle/>  y  y  y      
N3 RDF  y  y  y  y  y  y   
N3 Rules  y plus  y  y  y  y  y  y  
N3  y plus  y  y  y  y  y  y  y


      Acknowledgements

Sean Palmer and other folks on irc://openprojects.net/rdfig and later
irc://openprojects.net/swig suggested many things and reviewed new ideas
(and scrapped old ones!). Yosi Scharf created the parser test suites and
worked on consistency between grammar, test suites and code. Thanks to
all implementers on N3 software in all countries and langauges!

------------------------------------------------------------------------


    Historical Notes


      Numbers

Whilst complex numbers (with integer, rational or real parts) are a
reasonable class to add, it is not seen as a priority at the moment.

The literal syntax for decimals as 1.0 as opposed to double length reals
as 1.0e0 or 1e0 was decided in coordination with the DAWG working group
in January 2006.


      Boolean truth values

They were added to Notation3 in 2006-02 in discussion with the SPARQL
language developers, the Data Access Working Group. Note that no
existing documents will have used a naked true or false word, without a
|@keyword| statement which would make it clear that they were not to be
treated as keywords. Furthermore any old parser encountering true or
false naked or in a @keywords statement would throw an error, so
misunderstanding is avoided


      Mime Type History

[The type application/n3 was applied for in 2002 and again in 2006. The
IETF-W3C liaison meeting established that the mime type would be
formally awarded when the N3 specification was in a 'published' form. In
the mean time, it should be used as part of the point of N3 is to be
human readable, and so the text tree is indicated. The application for
text/rdf+n3 within the IANA registry is pending as of 2006-02 as IANA
#5004. While registration is pending, applications should use the
proposed type in anticipation of registration, *not* an x- type.]

In 2008-01, this specification was submitted as a W3C Team Submission.
Some discussion of the mime type occured, in hich the consesnsus
appeared to be that text/n3 was preferable to text/rdf+n3, and so that
change was adopted.

In 2008-01, there was some discussion also as to whether the encopding
parameter really was likely to be used in practical systems. That
general IETF architecture is outside the scope of the document.


    Appendix: Change History

2007/10
    @base introduced, and @prefix clarified.
2006/03
    N3Resources </DesignIssues/N3Resources> document split from this one.
2006/03
    The \ooo and \xhh escapes from dprocated to removed.
2006/01
    Added decimal literals, and true and false, in coordination with SPARQL.
2004/03
    The empty prefix is now bound by default to <#>
2003/03
    Added literal numbers
2003/02
    Added @forall @forsome
2001/04/10
    Removed \a, \b, \f, \v because they are not allowed in XML. Changed
    "ASCII character" to "byte" for \ooo and \xhh. (duerst)
2000/12/29
    Switched from bind to @prefix. Code still support sbind.

    Added ( node node ...) list shorthand, as code now reads and writes it.

    Added a little about self-describing documents.

------------------------------------------------------------------------


    References


      Normative

[RDFAS] /Resource Description Framework (RDF): Concepts and Abstract
Syntax/ W3C Recommendation 10 February 2004 </TR/rdf-concepts/>

[UTF8] F. Yergeau, /UTF-8, a transformation format of ISO 10646/, IETF,
RFC2279 <http://www.ietf.org/rfc/rfc2279.txt>

[UNF] Mark Davis, Martin Dürst, /Unicode Normalization Forms/
<http://www.unicode.org/unicode/reports/tr15/> , Unicode Consortium:
Unicode Standard Annex #15


      Informative

[NT]Jan Grant, David Beckett /RDF Test Cases/
<http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/> W3C
Recommendation, Section 3: "NTriples"

[BECK] D. Beckett, New Syntaxes for RDF
<http://www.dajobe.org/2003/11/new-syntaxes-rdf/paper.html> summarizes
the state of the art as of 2004.

[TURT] David Becket, /Turtle - Terse RDF Triple Language/
<http://www.dajobe.org/2004/01/turtle/>

[N3QL] N3QL </DesignIssues/N3QL.html>, a draft proposal for an RDF query
language.

[TUT]A tutorial </2000/10/swap/doc/Overview.html>

[OPSEM]/Notation 3 Logic/ </DesignIssues/N3Logic> An operational
semantics for N3.

Received on Wednesday, 16 January 2008 21:59:40 GMT

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