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Re: Comments to Semantic Web FAQ [2/2]

From: Ivan Herman <ivan@w3.org>
Date: Tue, 17 Apr 2007 13:36:13 +0200
Message-ID: <4624B12D.8090301@w3.org>
To: uldis.bojars@deri.org
CC: public-sweo-ig@w3.org
Comments below....

Uldis Bojars wrote:
> Hi All,
> Here are the remaining comments to the Semantic Web FAQ.
>> New questions:
> These questions, while maybe mentioned in other answers, deserve a FAQ
> entry.
>  >> What formats can RDF data be encoded / represented in ?
> RDF itself is a set of simple statements (triples) used to describe some
> data - information about resources and relations between them. 
> These statements can be encoded in a number of different formats - usually
> text-based (Turtle, Notation 3, ...) or XML-based (RDF/XML). Generally it
> does not matter which of these formats (or serialisations) is used to
> express data - the actual information is represented in RDF triples and the
> particular format is only the "syntactic sugar" which can be chosen
> depending on implementation preferences. Data can be freely converted from
> one format to another while keeping all the information described.

Hm. While I agree it is worth having a different question on this, there
was a significant overlap with the next question, so I moved some
paragraphs around, too. Here is how it looks now:

4.2. What formats can RDF be represented in?

RDF statements (or triples) can be encoded in a number of different
formats, whether XML based (e.g., RDF/XML) or not (Turtle, N-triples,
…). In general it does not really matter which of these formats (or
serialisations) are used to express data—the information is represented
in RDF triples and the particular format is only the “syntactic sugar”.
Most RDF tools can parse several of these serialization formats.

Compare to “numbers” as opposed to “numerals”. Numbers are mathematical
concepts; numerals are a representation thereof using Roman, Arabic,
hexadecimal, octal, etc, representations. Some of those representations
(like Roman) may be very complicated, some of those may be simpler or
more familiar, but they all represent the same abstract concept.

4.3. Isn’t RDF simply an XML application?

No. The fundamental model of RDF is independent of XML. RDF is a model
describing qualified (or named) relationships between two (Web)
resources, or between a Web resource and a literal. At that fundamental
level, the only commonality between RDF and the XML World is the usage
of the XML Schema datatypes to characterize literals in RDF.

Note that one of the serialization formats of RDF is indeed based on XML
(RDF/XML) and this is currently W3C’s standard encoding. But others
exist, see the separate question on RDF representation.

> Answer to "What is RDF?" (4.1.) says that information described in RDF forms
> a directed, labeled graph. This graph structure can be represented visually
> as a "nodes and arrows" diagram and is often used in examples as an
> easy-to-understand visual explanation. 
> "RDF Primer" [ http://www.w3.org/TR/rdf-primer/ ] is a good material for
> further reading on RDF.
> [ and contains examples in RDF/XML, text notation and their graphical
> representation ]

I have added a reference to the RDF Primer to the what is RDF question
rather than here.

> The link in 4.5. with link text "only one of the possible serialization" can
> then link to this answer. 

See above.

>>> How can I know if RDF data I am looking at is valid ?
> RDF data must be valid in order to correctly process them. 
> This is very much like XML which must be valid in order to correctly parse
> and process the information. For data represented in RDF/XML it must be
> valid XML with some additional requirements on top of that. You can use the
> W3C RDF Validator [ http://www.w3.org/RDF/Validator/ ] to check the validity
> of RDF/XML data and also render its graphical representation.
> You can also use any of the well known RDF frameworks (such as Jena or
> Redland) to parse and validate both text-based and RDF/XML representations
> of RDF. Redland, for example, contains a command-line tool called "rapper" [
> http://librdf.org/raptor/rapper.html ] which can parse various
> serialisations of RDF (and validation report errors if found) and convert
> them from one to another. 

I am not sure. This looks like a very technical, detailed issue to me.
If we do that, then this open the flood gates for a number of other
questions (how do I program RDF in Java, in C, in Python, etc etc), and
I am not sure I want to go there...

>> Existing questions:
>>> 1.2.  What are the major building blocks of the Semantic Web? 
> As already mentioned in previous email the 1st paragraph does not really
> list the fundamental building blocks, at least some of them are mentioned as
> differences.
> Suggestion: can leave most of the paragraph as is, and create a bullet list
> after it with 2 items (fundamental building blocks):
>  - "RDF, which is one of the fundamental building blocks of the Semantic
> Web, gives a formal definition for that interchange."
>  - URIs (add descriptive text here, can use some of the text in 1st
> paragraph )

I disagree. I explicitly tried to *avoid* using any specific technology
in that section, which is aimed at a higher level. I do not think having
a reference here to such technologies is appropriate...

> Link the "RDF" in first bullet to answer "4.1.  What is RDF?"
> Link the "URIs" in second bullet to answer "4.3.  Where is the "Web" in the
> Semantic Web?" in the formulation as suggested by Sandro.
>>> 1.4.  Will I "see" the Semantic Web in my everyday browser? 
> Add a paragraph:
> You can, however, see the "tip of an iceberg" or a human-readable display of
> RDF data attached to webpages by using tools such as PiggyBank and Semantic
> Radar. They are Firefox browser extensions which make use of RDF data which
> can be found on web pages (for example LiveJournal user pages). While end
> users will not have a need to see Semantic Web data (instead they will
> benefit from better information systems built on top of it) it may be
> helpful to developers to be aware of Semantic Web data present on web pages
> so that they can use this information in their applications.

Hm. Well, yes and no. I do not think this paragraph should go into this
question, it is too techie for that section. Also: the answer should not
only refer to tools that you have there (with all my due respect to the
Semantic Radar!:-), but should also refer to tools like Disco or the

I have therefore created a separate question:


3.10. Can I see Semantic Web data directly in my browser?

You can have a human-readable display of RDF data by using a number of
tools such as PiggyBank or Semantic Radar (which are Firefox extensions
to display Semantic Web data on a Web Page) or RDF data browsers like
the Tabulator, Disco, or the OpenLink RDF Browser. While end users will
not have a need to see Semantic Web data (instead they will benefit from
better information systems built on top of it) it may be helpful to
developers to be aware of Semantic Web data directly so that they can
use this information in their applications.

>>> 2.7. . microformats 
> The last part of the 1st sentence "and must be agreed upon by a community"
> does not distinguish microformats from ontologies in any way. Both must be
> agreed upon by a community or some body and for more complex ontologies can
> take quite some time. Suggest to remove this part. 

Although I have made a change "Microformats are usually relatively small
and simple sets of terms agreed upon by a community." I do not think
that statement is wrong. What this section says is that the "the
Semantic Web have the potential to be more expressive, rigorous, and
formal (and are usually larger)". I am not sure this paragraph should be
changed, to be hones.

> Practical eRDF [ http://keithalexander.co.uk/erdf-article/ ] article has
> some answers which we may use or reference to make this FAQ entry "sharper".
> See "When do I use Microformats, and when do I use eRDF?" and "use
> Microformats when / use eRDF when / use both at once!" entries.
> This article also has a FAQ entry about RDF: "But what is RDF anyway? and
> isn't it really complicated?"
> ( agree to what it's saying that fundamentally RDF is very simple )
> Data described in microformats each address a specific problem area (and
> they are usually used in XHTML when both human and machine readable data are
> included on the page). RDF can represent any information including that
> extracted from microformats present on the page. This is where microformats
> can benefit from RDF - as a universal format to store and query data coming
> from different microformats. 
> RDF as a separate "data page" linked to from a web page is also useful when
> the data on a particular web page and the machine readable data have
> different scope. E.g., when the first web page contains only a part of data
> available in a machine readable form (see "friends" list on many social
> software sites where the friends list is paged, but a pure machine-readable
> page such as FOAF may contain the full list of friends at once).

I rewrote the second paragraph in that section using some terms from above:

Data described in microformats each address a specific problem area. One
has to develop a program well-adapted to a particular microformat, to
the way it uses, say, the class and title attributes. It also becomes
difficult (though possible) to combine different microformats. In
contrast, RDF can represent any information—including that extracted
from microformats present on the page. This is where microformats can
benefit from RDF—the generality of the Semantic Web tools makes it
easier to reuse existing tools, eg, a query language and combining
statements from different origins easily belongs to the very essence of
the Semantic Web.

I do not feel that any more change is necessary, I must admit...

>>> 3.4.  Are the SW tools as robust and as ubiquitous as, say, the xerces
> XML parser? 
> "On the open source domain Jena [and Redland], for example, can easily be
> compared to xerces" - add a reference to Redland.

:-)By the time I got here, I had already added it:-)

>>> 3.5.  How do I put RDF into my (X)HTML Pages? 
> Make the sentence "The best solution is to store the RDF separately and use
> the URI-s to refer to the XHTML page and the link element in the XHTML page
> to refer to the RDF content." a separate paragraph. Add to it: "This
> technique is often called an RDF autodiscovery link."
> [ http://lists.w3.org/Archives/Public/semantic-web/2006Nov/0146.html ]
> contains links to more resources about RDF autodiscovery.
> May also add an example from the FOAF Specification (if needed): "The
> linking markup is as follows: <link rel="meta" type="application/rdf+xml"
> title="FOAF" href="http://example.com/people/~you/foaf.rdf" />"
> The link in 1st sentence with link text "usage of the meta and the link
> elements in the header" is broken.

I have separated the paragraph, added a sentence, but I prefer not to go
into the code details...

>>> 4.6.  What role do ontologies and/or rules have on the Semantic Web? 
> Add hyperlinks to information about rules on the web. 
> Notation3 can be mentioned as a language that one can write rules in.

Hm. I would prefer work out a separate Q-A on rules. Will work on it.

>>> 4.12. Will W3C be standardizing any particular ontologies? 
> Add SIOC [ http://rdfs.org/sioc/spec/ ] to the list of community-developed
> ontologies in the 1st paragraph.
> ---
> That's all of the comments.
> Uldis
> [ http://captsolo.net/info/ ]


Ivan Herman, W3C Semantic Web Activity Lead
URL: http://www.w3.org/People/Ivan/
PGP Key: http://www.cwi.nl/%7Eivan/AboutMe/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Tuesday, 17 April 2007 11:55:59 UTC

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