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Re: how to define that a relation is a dataype?

From: Story Henry <henry.story@bblfish.net>
Date: Sat, 6 Mar 2010 02:05:40 +0100
Cc: Jeremy Carroll <jeremy@topquadrant.com>, Dan Connolly <connolly@w3.org>, Semantic Web <semantic-web@w3.org>, foaf-protocols@lists.foaf-project.org
Message-Id: <412D104C-2247-45AB-8655-132B3BBA5280@bblfish.net>
To: Pat Hayes <phayes@ihmc.us>

On 5 Mar 2010, at 20:13, Pat Hayes wrote:

> Henry, congratulations. I think you are the fastest and most thorough reader that the RDF semantics document has ever had :-)

It did take a few weeks to read, and I have not digested all of it. :-)

> But let me ask you. Suppose, just for arguments sake, that RDF allowed literals in the subject position.

In N3 it does, and it seems like a good idea. After all, any relation has its inverse, so it is clear that such relations must exist. To have syntactic restrictions on graphs of as specified in current RDF seems somewhat arbitrary. (Though one can see how it came about as an attempt to adapt to xml)

I suppose that if you have literals as subjects you could have relations that are non functional too. For example

"Henry" foaf:firsnameOf hKissinger, bblfish, ....

> Then one could write
> 
> ex:o ex:dollarValue _:v .
> "BA:BA" cert:hex _:v .
> 
> and cert:hex would be the actual L2V mapping of the datatype, rather than its inverse.

yes. It is true that this also makes sense.

>    If this were legal RDF, would you have any objection to doing it that way? (Because, I am sure that any revision of RDF will allow literals as subjects.) Are there other reasons which motivate your choice of the 'inverse' orientation for the second triple?

I think that would be ok too.

The advantage of the proposed solution is that it works now, and so we don't have to wait for a new revision of RDF to come along, which could take a lot of time to mature. (but then I was asking for such a revision...)

Even if that happened, as pointed out above, the fact that literals can be subjects is larger than the ^^ or the datatype= notation, as those are very specifically for functional L2V values. 

It is certainly true that the above does not constitute a decisive argument.

How would I define cert:hex as a datatype currently though? Is this even something one can write down?

perhaps

cert:hex a rdfs:Datatype;
    owl:equivalentClass xsd:nonNegativeInteger;
    rdfs:comment "An encoding of a...." .

That also seems reasonable.

Perhaps for cert:hex we'll have to have a time of transition from one interpretation to the neutral one, which is open to both further interepretations....

Perhaps others have some thoughts on this...



	Henry

> 
> Pat
> 
> 
>> ex:o ex:dollarValue _:v .
>> _:v cert:hex "BA:BA" .
> 
> 
>> ex:o ex:dollarValue _:v .
> 
> 
> On Mar 5, 2010, at 11:55 AM, Story Henry wrote:
> 
>> I have read most of the "RDF semantics" document carefully now, and I think I have enough detailed understanding to try to recapitulate the discussion, and explain in detail my reasons.
>> 
>> 
>> STARTING WITH AN EXAMPLE: cert:hex
>> ===================================
>> 
>> 1. proposed definition of cert:hex
>> ----------------------------------
>> 
>> I can defined cert:hex as follows (though the detailed wording could be improved)
>> 
>> @prefix : <http://www.w3.org/ns/auth/cert#> .
>> @prefix owl: <http://www.w3.org/2002/07/owl#> .
>> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
>> @prefix vs: <http://www.w3.org/2003/06/sw-vocab-status/ns#> .
>> 
>> 
>> :hex a owl:DatatypeProperty, rdfs:Datatype,
>>     owl:InverseFunctionalProperty;
>>  rdfs:label "hexadecimal"@en;
>>  rdfs:comment """
>>  An encoding of a positive integer (from 0 to infinity) as a hexadecimal string that makes it easy to read and/or fun to present on the web.
>>  The purpose of this way of representing hexadecimals is to enable users to copy and paste hexadecimal notations as shown by most browsers, keychains or tools such as opensso, into their rdf representation of choice.  There are a wide variety of ways in which such strings can be presented. One finds the following
>> 
>> e1 dc d5 e1 00 8f 21 5e d5 cc 7c 7e c4 9c ad 86
>> 64 aa dc 29 f2 8d d9 56 7f 31 b6 bd 1b fd b8 ee
>> 51 0d 3c 84 59 a2 45 d2 13 59 2a 14 82 1a 0f 6e
>> d3 d1 4a 2d a9 4c 7e db 90 07 fc f1 8d a3 8e 38
>> 25 21 0a 32 c1 95 31 3c ba 56 cc 17 45 87 e1 eb
>> fd 9f 0f 82 16 67 9f 67 fa 91 e4 0d 55 4e 52 c0
>> 66 64 2f fe 98 8f ae f8 96 21 5e ea 38 9e 5c 4f
>> 27 e2 48 ca ca f2 90 23 ad 99 4b cc 38 32 6d bf
>> 
>> Or the same as the above, with ':' instead of spaces. We can't guarantee that these are the only ways such tools will present hexadecimals, so we are very lax.
>> The letters can be uppercase or lowercase, or mixed.   Some strings may start with initial 00's, and can be stripped in this notation as they often are. Doing this could in complement of 2 notation could turn a positive number into a negative one, if the first character after applying the transformation described below, then happens to be one of  the set {'8', '9', 'a', 'A', 'b', 'B', 'c', 'C', 'd', 'D', 'e', 'E', 'f', 'F'} .  But as we interpret this string as a hexadecimal number leading 00s are not important  (Complement of 2 notation and hexadecimal overlap for positive numbers)
>> 
>> In order to make this fun, we allow any unicode characters in the string.
>> 
>> A parser should
>> 1. remove all non hexadecimal characters
>> 2. treat the resulting as a hexadecimal representation of a number
>> This will allow people to make an ascii - better yet a UTF-8 - picture of their
>> public key when publishing it on the web.
>>  """@en;
>> rdfs:seeAlso <http://en.wikipedia.org/wiki/Hexadecimal>;
>> rdfs:domain xsd:nonNegativeInteger;
>> rdfs:range xsd:string;
>> vs:term_status "unstable" .
>> 
>> 
>> 2. Example interpretation
>> -------------------------
>> 
>> 
>> So if I take the triple
>> 
>> ex:o ex:dollarValue _:v .
>> _:v cert:hex "BA:BA" .
>> 
>> which can be written as
>> 
>> ex:o ex:dollarValue "BA:BA"^cert:hex .
>> 
>> This is equivalent to the relation to the literal
>> 
>> ex:o ex:dollarValue "BA:BA"^^cert:hex .
>> 
>> 
>> so here in addition to the RDF, RDFS and OWL vocabularies we have
>> 
>> V = { "http://www.w3.org/ns/auth/cert#hex", "ex:o", "0", ...,"AB:AB",
>>    "BA:BA"^^cert:hex, ex:dollarValue, "_:v" }
>> 
>> and an Interpretation I
>> 
>> IR = { cert:hex, ex:o } U xsd:nonNegativeIntegers U IR(rdf) U IR(rdfs) U IR(owl)
>> 
>> IP = { cert:hex, ex:dollarValue } U IP(rdf) U IP(rdfs) U IP(owl)
>> 
>> IEXT : { cert:hex => { <0 "0" > <1 "1"> ....
>>                      <47802 "AB:AB"> <47802 "AB AB"> <47802 "AB|AB">
>>                     ...}
>>        ex:dollarValue => { <ex:o 47802> }
>>       U IEXT(rdf) U IEXT(rdfs) U IEXT(owl)
>> 
>> IS : { "ex:o" => <ex:o>
>>      "http://www.w3.org/ns/auth/cert#hex" => cert:hex
>>     } U IS(rdf) U IS(rdfs) U IS(owl)
>> 
>> IL : { "0"^^xsd:hex => 0
>>      "1"^^xsd:hex => 1
>>      "2"^^xsd:hex => 2
>>       ...
>>      "AB:AB"^^cert:hex => 47802
>>      "AB AB"^^cert:hex => 47802
>>      ... } U IL(rdf) U IL(rdfs) U IL(owl)
>> 
>> LV = LV(rdf)
>> 
>> Using this interpretation, which is very general, we can see that the following graph makes both of them true
>> 
>> 
>> <cert_hex.jpg>
>> 
>> 
>> [ Here IEXT' is the relation from an object directly to an instance relation,
>> which is easier to draw, than drawing the line to the set of ordered pairs
>> The same with L2V' . ]
>> 
>> 3. Proving Satisfaction
>> ------------------------
>> 
>> Take the graph G composed of the triple
>> 
>> ex:o ex:dollarValue "BA:BA"^^cert:hex .
>> 
>> That is a ground triple, so it is true if as specified in section 1.4
>> http://www.w3.org/TR/rdf-mt/#gddenot
>> 
>> + "ex:o", "ex:dollarValue", "BA:BA"^^cert:hex are in V
>> + I(ex:dollarValue) is in IP
>> + <I("ex:o") I("BA:BA"^^cert:hex)>
>>        = < ex:o, IL("BA:BA"^^cert:hex)>
>>        = < ex:o, 47802 >
>>   which is indeed (amazing!) in IEXT(I("ex:dollarValue"))
>> 
>> 
>> Similarly if we now take the graph G2 composed of the two triples
>> 
>> G2 = {
>> t1 = { ex:o ex:dollarValue _:v .}
>> t2 = { _:v cert:hex "BA:BA" . }
>> }
>> 
>> I(G2) = true if [I+A](G2) for some mapping from blank(G2) to IR.
>> 
>> So we will cleverly select a mapping A such that
>> 
>> A("_:v") = 47802
>> 
>> And now the above graph is true if there is no triple T in G2 such that I(T) = false .
>> 
>> Luckily for the readers of this there are only two triples, so we proceed one by one
>> 
>> t1= { ex:o ex:dollarValue _:v .}
>> 
>> + "ex:o" "ex:dollarValue" "_:v" are in V
>> + I(ex:dollarValue) is in IP    -- as above
>> + <I+A("ex:o") I+A("_:v")>
>>     = <ex:o A("_:v")>
>>     = <ex:o 47802>
>> which is indeed (amazing!) in IEXT(I+A("ex:dollarValue")) = IEXT(I("ex:dollarValue"))
>> 
>> t2 = { _:v cert:hex "BA:BA" . }
>> 
>> + "_:v" "http://www.w3.org/ns/auth/cert#hex" "BA:BA" are in V
>> + I(cert:hex) is in IP
>> + <I+A("_:v") I+A("BA:BA")>
>>   = <A("_:v") I("BA:BA")>
>>   = <47802 "BA:BA">
>> which is in IEXT(I+A("cert:hex"))
>> 
>> So both not of those are false so the graph G2 is true.
>> 
>> 
>> cert:hex Datatype GENERALISATION
>> ================================
>> 
>> Let's look at the cert:hex datatype in more detail following section 5
>> http://www.w3.org/TR/rdf-mt/#dtype_interp
>> 
>> [[
>> Formally, a datatype d is defined by three items:
>> 
>> 1. a non-empty set of character strings called the lexical space of d;
>> 2. a non-empty set called the value space of d;
>> 3. a mapping from the lexical space of d to the value space of d, called the lexical-to-value mapping of d.
>> 
>> The lexical-to-value mapping of a datatype d is written as L2V(d).
>> ]]
>> 
>> Take the conditions one by one.
>> In our case
>> 1. is the set of all unicode strings
>> 2. the value space are all the positive integers including 0
>> 3. and the lexical to value maping is explained in the definition of cert:hex
>> 
>> L2V(cert:hex)("AB AB") = 47802
>> L2V(cert:hex)("AB:AB") = 47802
>> L2V(cert:hex)(" 0") = 0
>> L2V(cert:hex)("♡AB♥AB♡") = 47802
>> 
>> now L2V is functional relation. So it has an inverse relation, that will be inverse functional. That is what IEXT(cert:hex) is. So let us define the INV function that maps a set of ordered pairs to its inverse, namely for every ordered pair <xxx yyy> in the origin set there will correspond one to one an ordered pair <yyy xxx> in the resulting set.
>> 
>> It is clear that the relation
>> 
>> INV(L2V(cert:hex)) = IEXT(cert:hex)
>> 
>> and vice versa.
>> 
>> As this can be generalised to all datatypes, I suggest that in the next revision of the RDF Semantics this is added.
>> 
>> 
>> PRAGMATIC REASONS FOR DOING SO
>> ==============================
>> 
>> 
>> Now what is the value of doing so?
>> 
>> In a previous mail to this thread Pat Hayes argued very convincingly that the reason one URI refers in different ways to different things, is to reduce the need to create many URIs for each different thing.
>> 
>>  http://lists.w3.org/Archives/Public/semantic-web/2010Feb/0193.html
>> 
>> So this is exactly the same reason why datatypes should be associated not just as they are now
>> - with the set of objects when used in object position
>> - with the L2V function when in the position of a datatype
>> But also
>> - with the INV(L2V(ddd)) when in a predicate position
>> 
>> Helping show how predicates and datatypes are related makes it much easier in my opinion to understand datatypes. There is nothing that magical about them.
>> 
>> It is very useful to have both pragmatically. So for example if as we have now we only had relations then we would have to write
>> 
>> <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
>> <body>
>> <ul xmlns:cert="http://www.w3.org/ns/auth/cert#"
>>    xmlns:rsa="http://www.w3.org/ns/auth/rsa#" >
>>    <li rel="rsa:modulus">
>>      <pre property="cert:hex">
>> 9dcfd6a5394da9312c703e02a25dc3508262d9310be76d43ddf75d3025a9
>> 739b989b2e50f2a80961fe41e6fb26fb7ceedae0fe0e0c7c1921f20a3a63
>> 45fe74e9</pre>
>>    </li>
>>    <li rel="cert:identity" href="#me">My certificate</li>
>> </ul>
>> </body>
>> </html>
>> 
>> but because we have datatypes we can also write much more succintly
>> 
>> <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
>> <body>
>> <ul xmlns:cert="http://www.w3.org/ns/auth/cert#"
>>    xmlns:rsa="http://www.w3.org/ns/auth/rsa#"
>>    typeof="rsa:RSAPublicKey" >
>>   <li property="rsa:modulus" datatype="cert:hex">
>> 9dcfd6a5394da9312c703e02a25dc3508262d9310be76d43ddf75d3025a9
>> 739b989b2e50f2a80961fe41e6fb26fb7ceedae0fe0e0c7c1921f20a3a63
>> 45fe74e9</li>
>>  <li rel="cert:identity" href="#me">My certificate</li>
>> </ul>
>> </body>
>> </html>
>> 
>> The second way of writing furthermore helps remove the danger of the literal
>> getting a language tag inherited from further up.
>> 
>> FURTHER THOUGHT
>> ===============
>> 
>> One could associate every language tag, with a URL, and following the same procedure show
>> how a language tag is a relation, as well as whatever it is right now.
>> 
>> 
>> Sorry to go into such detail.
>> 
>> The RDF Semantics paper is really extreemly intersting merge of logic and graph theory.
>> 
>> 
>> Henry
>> 
>> 
>> On 22 Feb 2010, at 22:42, Jeremy Carroll wrote:
>> 
>>> Pat Hayes wrote:
>>>> Dan is absolutely correct. See below.
>>>> 
>>>>> 
>>>>> I don't think so. I'm pretty sure the 2004 specs are silent on the
>>>>> use of datatypes as properties. Both directions are consistent
>>>>> semantic extensions.
>>>> 
>>>> Yes, you are right. So this semantic extension is perfectly legal, contrary to what I was claiming. <Sound of crows being eaten />
>>>> 
>>>> Sigh. However, it seems utterly crazy to me to use the same URI to denote both a mapping (inside a typed literal) and its inverse mapping (as a property). If I had even thought that anyone would want do that, I would have urged that we made it illegal back when we were writing the specs. The only possible reason for it that I can see would be to set out to make things deliberately confusing.
>>> 
>>> I find Henry's examples fairly compelling, and wouldn't want them to be illegal. Not something I would do myself, but certainly plausible.
>>> 
>>> Jeremy
>>> 
>>> 
>> 
> 
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Received on Saturday, 6 March 2010 01:06:20 UTC

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