Hi Yihong:
I am a big fan of Codd's "one fact in one place" credo. However, in this
particular case, that principle is violated anyway, since the literal
values are often duplicated for presentation and meta-data prupolses
anyway (think of "2009-06-29" vs. "June 29, 2009"). Second, for dynamic
Web apps, it does not really matter whether the same fact is exposed
once or twice, since the central location is one place in the database
anyway. Third, this is the only way how a tool like the GoodRelations
annotator [1] can create RDFa snippets for simple copy-and-paste into
existing pages.
Also note that in the particular case of RDFa, the principle of "one
fact in one place" clashes with the "separation of concerns" principle,
in particular, that of keeping data and presentation separate.
The textbook-style "beauty of simplicity" of RDFa holds for adding a
dc:creator property to a string value that is the same for presentation
and at the data level. Beyond that, RDFa can create code that is very
hard to maintain. In fact, I know that a large software company
dismissed the use of RDFa in their products because of the unmanageable
mix of conceptual and presentation layer.
As far as security is concerned: I there is no real difference in my
proposal, as the "content" attribute of RDFa allows serving different
data to human and to machines, and this is a needed feature anyway.
Digital signatures at the document or element level and / or data
provenance approached will likely cater for that.
Best
Martin
Yihong Ding wrote:
Hi Kingley and Martin,
A potential problem of the model Martin suggested is that the same data has
to be presented at least TWICE in one document. Although the RDFa portion of
the data is supposed to be automatically generated, it, however, does not
prohibit anybody from manually revising it. Therefore, it leaves a huge hole
for the hackers (or anybody who want to do some deceptive job). In our
imperfect world, this problem is severe.
Adding an extra layer of data mapping always causes additional work on data
maintenance. This time, the extra work could be a nightmare though the
architecture is neat.
yihong
On Mon, Jun 29, 2009 at 8:03 AM, Kingsley Idehen <kide...@openlinksw.com>wrote:
Martin Hepp (UniBW) wrote:
Hi Tom:
Amen. Thank you for writing this. I completely agree. RDFa has some
great use cases but (like any technology) has its limitations. Let's
not oversell it.
We seem to agree on the observation, but not on the conclusion. What I
want and suggest is using RDFa also for exchanging a bit more complex RDF
models / data by simply using a lot of div / span or whatever elements that
represent the RDF part in the SAME document BUT NOT too closely linked with
the presentation level.
<body>
<h1>This is the car I want to sell</h1>
Actually, a pretty cool car, for only $1.000. Offer valid through July 31,
2009
<span>
... my whole RDF in RDFa
</span>
<body>
The advantage of that would be that
- you just have to maintain ONE file,
- data and metadata are close by, so the likelihood of being up to date
increases, and
- at the same time, the code does not get too messy.
- Also - no problems setting up the server (*).
- Easy to create on-line tools that generate RDFa snippets for simple
pasting.
- Yahoo and Google will most likely honor RDFa meta-data only.
Also note that often the literal values will be in content attributes
anyway, because the string for the presentation is not suitable as meta-data
content anyway (e.g. dates, country codes,...)
I think the approach sketched above would be a cheap and useful way of
publishing RDF meta-data. It could work with CMS / blogging software etc.
Imaging if we were able to allow eBay sellers to put GoodRelations
meta-data directly into the open XHTML part of their product description.
The main problem with my proposal is that there is the risk that Google
considers this "cloaking" and may remove respective resources from their
index (Mark raised that issue). If that risk was confirmed, we would really
have a problem. Imagine me selling Semantic Web markup as a step beyond SEO
... and the first consequence of following my advice is being removed from
the Google index.
A second problem is that if the document contains nodes that have no
counterpart on the presentation level (e.g. intermediate nodes for holding
n-ary relations), then they will also not be dereferencable. The same holds
for URIs or nodes that are outside the scope of the actual RDFa / XHTML
document - I see no simple way of serving neither XHTML nor RDF content for
those.
Martin,
If Google doesn't see invisible DIVs as cloaking, the issue vaporizes.
Also, if people take the SEO + SDQ (Linked Data Expressed in RDFa) approach
they will at least remain in the Google index via usual SEO oriented keyword
gimmickry, albeit generally suboptimal.
If we make a recipe doc showcasing these issues, we will more than likely
get Google to recalibrate back to the Web; especially if we can demonstrate
that other search engine players --that have support RDFa -- not being
afflicted with the same cloaking myopia.
Kingsley
Best
Martin
Tom Heath wrote:
Martin,
2009/6/27 Martin Hepp (UniBW) <martin.h...@ebusiness-unibw.org>:
So if this "hidden div / span" approach is not feasible, we got a
problem.
The reason is that, as beautiful the idea is of using RDFa to make a)
the
human-readable presentation and b) the machine-readable meta-data link
to
the same literals, the problematic is it in reality once the structure
of a)
and b) are very different.
For very simple property-value pairs, embedding RDFa markup is no
problem.
But if you have a bit more complexity at the conceptual level and in
particular if there are significant differences to the structure of the
presentation (e.g. in terms of granularity, ordering of elements, etc.),
it
gets very, very messy and hard to maintain.
Amen. Thank you for writing this. I completely agree. RDFa has some
great use cases but (like any technology) has its limitations. Let's
not oversell it.
Tom.
--
--------------------------------------------------------------
martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen
e-mail: mh...@computer.org
phone: +49-(0)89-6004-4217
fax: +49-(0)89-6004-4620
www: http://www.unibw.de/ebusiness/ (group)
http://www.heppnetz.de/ (personal)
skype: mfhepp twitter: mfhepp
Check out the GoodRelations vocabulary for E-Commerce on the Web of Data!
========================================================================
Webcast:
http://www.heppnetz.de/projects/goodrelations/webcast/
Talk at the Semantic Technology Conference 2009: "Semantic Web-based
E-Commerce: The GoodRelations Ontology"
http://tinyurl.com/semtech-hepp
Tool for registering your business:
http://www.ebusiness-unibw.org/tools/goodrelations-annotator/
Overview article on Semantic Universe:
http://tinyurl.com/goodrelations-universe
Project page and resources for developers:
http://purl.org/goodrelations/
Tutorial materials:
Tutorial at ESWC 2009: The Web of Data for E-Commerce in One Day: A
Hands-on Introduction to the GoodRelations Ontology, RDFa, and Yahoo!
SearchMonkey
http://www.ebusiness-unibw.org/wiki/GoodRelations_Tutorial_ESWC2009
--
Regards,
Kingsley Idehen Weblog:
http://www.openlinksw.com/blog/~kidehen<http://www.openlinksw.com/blog/%7Ekidehen>
President & CEO OpenLink Software Web: http://www.openlinksw.com
--
--------------------------------------------------------------
martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen
e-mail: mh...@computer.org
phone: +49-(0)89-6004-4217
fax: +49-(0)89-6004-4620
www: http://www.unibw.de/ebusiness/ (group)
http://www.heppnetz.de/ (personal)
skype: mfhepp
twitter: mfhepp
Check out the GoodRelations vocabulary for E-Commerce on the Web of Data!
========================================================================
Webcast:
http://www.heppnetz.de/projects/goodrelations/webcast/
Talk at the Semantic Technology Conference 2009:
"Semantic Web-based E-Commerce: The GoodRelations Ontology"
http://tinyurl.com/semtech-hepp
Tool for registering your business:
http://www.ebusiness-unibw.org/tools/goodrelations-annotator/
Overview article on Semantic Universe:
http://tinyurl.com/goodrelations-universe
Project page and resources for developers:
http://purl.org/goodrelations/
Tutorial materials:
Tutorial at ESWC 2009: The Web of Data for E-Commerce in One Day: A
Hands-on Introduction to the GoodRelations Ontology, RDFa, and Yahoo!
SearchMonkey
http://www.ebusiness-unibw.org/wiki/GoodRelations_Tutorial_ESWC2009
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