Re: I guess it's a stupid questions...

----- Original Message -----
From: Stefano Mazzocchi <stefano@apache.org>
To: Michael Henson <mike@axl.net>
Subject: Re: I guess it's a stupid  questions...
Date: Fri, 12 Nov 2004 15:12:10 -0500

> 
> 
> Michael Henson wrote:
> > On Sat, 2004-11-13 at 02:42 +0800, Petko Petkov wrote:
> > 
> >>I guess it’s a stupid question, but I still do not understand why RDF is better than just XML.
> >>I understand that XML is just an approach of describe other markup languages and I believe that
> >>RDFS goes on the top of XML. That’s great, but, we are making our lives harder again and again.
> >>Simple XML tags are much powerful than RDF statements and the triplets can be represented in much
> >>simpler way using namespaces. 
> >>
> >>I have read somewhere that XML and XML Schemas are not good because XSD implies specific rules on
> >>the document structure. I find this explanation rather stupid than complete. XSD have the capabilities
> >>to include into a particular element different elements that may come from different namespace for example. 
> >>I examined Firefox structure to see real RDF examples. Although, Firefox is just the best browser in the
> >>world, RDFS can be replaced by XML.
> >>
> >>Can somebody explain to me?
> >>
> >>Thanks
> >>
> > 
> > 
> > The following article is a decent RDF is not XML intro:
> > http://www.betaversion.org/~stefano/linotype/news/57/
> 
> and in really short terms:
> 
>   the XML model has implicit relationships between items, the RDF model 
> makes them explicit.
> 
> So, they are equivalent in term of semantic interoperability of 
> concepts, but they are not in terms of relationships (you need a more 
> constrained XML model, which is what RDF/XML gives you).
> 
> If you don't care about semantic interoperability of relationships, keep 
> using XML and be happy. There is nothing wrong in that, but the rest of 
> the world won't be able to understand your data, even if properly 
> namespaced because the "meaning" of the nesting of the tags will have to 
> be 'guessed' by the XML reader.
> 
> But if you care about other people using your data without having to 
> guess their internal relationships, use RDF, or make those relationships 
> explicit by XSLT transforming your XML into RDF (here, the XSLT will 
> contain the information that is missing in the XML model).
> 
> For more info, you might also want to read Part II of my guide:
> 
> http://www.betaversion.org/~stefano/linotype/news/78/
> 
> Oh, and it's not a stupid question at all. Actually is a really really 
> good one and the fact that XML people don't get why RDF is needed is 
> because the implicitness of relationships is not something that is 
> bothering people in the XML world since the missing logic is normally 
> hardcoded in the application that create and digest a particular XML schema.
> 
> Coming from that camp, I can tell you that once you start publishing 
> data without knowing how others are going to use it, well, you do find 
> XML pretty limiting.
> 
> Take this fragment
> 
>   <1 xmlns="urn:blah:" rdf:about="urn:blah:0">
>     <2>blah</2>
>   </1>
> 
> let's now interpret it as XML. What is the relationship between 
> urn:blah:1 and urn:blah:2? well, "isContainedIn" is the only 
> relationship that we can infer, but what did the schema author wanted to 
> imply with this nesting? behavior? property? denomination?
> 
> Who knows.
> 
> [if you think this is never the case, imagine to receive a SOAP envelope 
> with a properly namespaced chinese payload and imagine writing the code 
> that handles that!]
> 
> Now interpret the above as RDF/XML, it says:
> 
>   - there is a resource "urn:blah:0"
>   - this resource has type "urn:blah:1"
>   - this resource has a relationship urn:blah:2 with a literal value of 
> "blah"
> 
> same syntax, different models. With RDF, the readers of your data can 
> guess less and know more.
> 
> Is this enough to solve the semantic interoperability problem? not at 
> all, but it's a step forward.
> 
> In short, if you can't send logic along with your data (a big security 
> threat these days!), you have to encode it somehow.
> 
> RDF helps.
> 
> -- 
> Stefano.
> 
> 
> 


Hi Stefano,
I read your article long time ago and I clearly understand what the benefits of RDF are. Still I do not understand one thing. I will try to show it with an example:

We have a page and it is xml encoded. For example:
<!—quick search for “dolphins” in google -->
<page>
 <title>This is my page</title>
 <content>
  <title>This document is about the dolphins</title>
  <para>Nineteen centuries ago, Plutarch, a Greek moralist and biographer made this statement: "to the dolphin alone, beyond all other, nature has granted what the best philosophers seek: friendship for no advantage". 1 In our own times Barbara Tufty made the comment "he [Dolphins] also exhibits a friendly willingness to cooperate with other earth creatures -- a rare attribute which another animal, Homo Sapiens, has not yet learned to do with any consistency".2 Apparently there is something quite impressive about Dolphins. Not only now, when we are learning so much more about them, but even in the year 62 AD! </para>
  <para>Outside of his striking friendliness, the Dolphin seems to have been blessed with a well developed sense of humor. Dolphins have been known to silently maneuver behind an unsuspecting pelican and snatch its tail feathers -- usually leaving the bird minus a few. Other pranks include grabbing unsuspecting fish by the tail, pulling them backward a few feet as well as bothering slow turtles by rolling them over and over. Once a dolphin was seen placing a piece of squid near a grouper's rock cranny. When the fish came out, the dolphin promptly snatched the bait away, leaving the puzzled fish behind.
</para>
</content>
</page>

quotes from: http://www.littletownmart.com/dolphins/

So far this page is meaningless to computers, right? Now I can put some triplets on the top and I can say that I am the author and so on. I can make some relationship to other resources on the web as well. I can put the quotations in rdf as well. It is true that the semantics can be applied using XSLT on the fly, but I find this approach not very reasonable, because we generalize conceptually the problem instead of putting everything in its own logical concept.

Using the page above means that I have to take every kind of relationship and explicitly state it with RDF. However this will make my page redundant and every single change will require additional changes in the meta data.

You may thing that this is unnecessary to do but have a look on the following example. It will be very beneficial if the next version of Acrobat Reader has more advance search function so I can quickly relate on section of “your book” to another section for the same book. However, this means that I have to write the relationships in RDF. This process might be long but achievable. However, it is redundant. It will be much better if I can put all relationships on the fly without going back and forward to RDF. I am working on something that might resolve this problem and I will post it as soon as I make some corrections.

I think that rdf is great when you are describing data that is used by software that already knows what is the data about. I guess this explanation sounds funny. Sorry about that. English is my second language. Anyway, a typical example is Firefox. Firefox uses RDF entities to describe the internal structure of the application. At the beginning Firefox loads all rdf files. The overall meta file is aggregated on the fly. Now every single extension can make some corrections to add different functionalities in any part of Firefox. The idea is great. However, Firefox already knows what to expect. You can use XML documents and aggregate all of them in a single proxy document and you have the same thing.

RDF is a step forward; at least it makes us think how the data can be represented in a way so computers can understand it. However, RDF is a data about data that generates a lot of data. It’s hard to imagine building a huge portal that consists of many RDF documents, coming from different users and describing different things, both accessible to computers and humans.

-- 
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Received on Friday, 12 November 2004 20:54:27 UTC