- Answer
-
The W3C Semantic Web Interest Group is one of those and probably the best place
to join first. It is a public mailing list and is also active on the #swig IRC channel
Freenode.
There are also various grass-root communities that concentrate on some specific
aspects or goal around the Semantic Web. Some examples:
DOAP: a project to describe information about open-source software projects
FOAF: a project to describe information about people and their social relations
(see also the #foaf IRC channel on Freenode)
SIOC: a project to describe information about online community sites (blogs,
bulletin boards, …) and use this information to connect these sites together.
Linking Open Data on the Semantic Web: is project whose goal is to make various
open data sources available on the Web as RDF and to set RDF links between data items
from different data sources.
Another source is the PlanetRDF Blog aggregator that aggregates the blogs of
a number active Semantic Web developers from around the World.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Is there a community of developers I can join?
- Answer
-
First of all, as pointed out elsewhere in this document, one can develop Semantic
Web applications without using ontologies. Very useful applications can be built without
those, relying on the most fundamental, and simple concept of the Semantic Web. However,
even if ontologies, rules, reasoners, etc, are used, the average user should not care
about the complexities of, say, the details of reasoning. All this is done “under
the hood”. What the developer needs to operate with are usually simple logical patterns
of the sort “Given that (Flipper isA Dolphin) and (Dolphin isAlso Mammal), one can
conclude that (Flipper isA Mammal)".
Compare it to SQL. The official SQL standards, the formal semantics of SQL, and
indeed its implementations, are extremely complex and understood by a few specialists
only. Nevertheless, a large number of users use SQL in practice, without caring about
the underlying complexities.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- Does one have to understand the theory of formal ontologies and logic to use the Semantic
Web?
- Answer
- There are and there aren't. There is just the way the Web raises this issue already;
after all, documents browsed by a traditional browser are usually cached on the client
side. And there aren't, because this does not seem to have created major problems
on the Web so far, and the Semantic Web is not fundamentally different in this respect.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- Aren't there major copyright questions if the data in an integration process are cached?
- Title
- Description of a Project
- Answer
-
There are several portals that collect information on existing ontologies. A
good example is SchemaWeb. Another one is the “PingTheSemanticWeb” service which collects
information about new RDF documents on the Web based on “pings” sent by applications
generating data and on RDF autodiscovery links found by people browsing the Web. It
currently contains information about ~7 million RDF files. There are also search engines,
like Falcon, Sindice, or Watson and others (see the separate section on the tool’s
wiki page) that specialize on searching Semantic Web documents.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Where do I find ontologies, terminologies, or datasets for my applications?
- Label
- How do I participate in the Semantic Web?
- Label
- How does the Semantic Web relate to…
- Answer
-
As all innovative technologies, the Semantic Web underwent an evolution starting
at research labs, being then picked up by the Open Source community, then by small
and specialized startups and finally by business in general. Remember: the Web was
originally developed in a High Energy Physics center!
At present, the Semantic Web is increasingly used by small and large business.
Oracle, IBM, Adobe, Software AG, or Yahoo! are only some of the large corporations
that have picked up this technology already and are selling tools as well as complete
business solutions. Large application areas, like the Health Care and Life Sciences,
look at the data integration possibilities of the Semantic Web as one of the technologies
that might offer significant help in solving their R&D problems.
It is worth consulting the list of Semantic Web Case Studies and Use Cases; it
gives a good overview of existing applications. Note that the list is often updated,
when new application examples come in.
- Date
- 2007-07-29T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- Is the Semantic Web just research, or does it have industrial applications?
- Name
- Ivan Herman
- Personal mailbox
- mailto:ivan@w3.org
- Answer
-
Dave Beckett's Resource Description Framework (RDF) Resource Guide gives a quite
comprehensive list of references to Semantic Web related articles. The home page of
the Semantic Web Activity lists all the recommendations, gives references to some
of the presentations, articles, etc, that have been given by the W3C staff or the
members of the working groups on the subject. A separate page lists a number of tutorials
that might be of interest.
The (now defunct) Semantic Web Best Practices and Deployment Working Group has
produced a number of notes that might be useful when developing ontologies, setting
up servers to serve RDF data, using XML Schema datatypes with RDF, etc.
A number of books have also been published. A list of books is given on W3C’s
Wiki site, comprising (at this moment) over 40 books in different languages, published
by major publishers like O’Reilly, MIT Press, Cambridge University Press, Springer
Verlag, …
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- How can I learn more about the Semantic Web?
- Answer
-
The problem referred to by this question is the fact that, in formal logic, if
there is an inconsitency somewhere, then it is possible to draw all conclusions
and their negations. The issue is whether this would not create major difficulties
on the Semantic Web.
“Inference” in terms of the Semantic Web can be characterized by discovering
new relationships (as explained in the answer of another question). These inferences
are mostly done within a restricted, “guarded” subset of first order logic. Usually,
reasoning on the Semantic Web does not use the full power of first order (or higher
order) logic, and therefore avoids some of the dangerous issues that can come from
an inferred inconsistency. In other words, in practice, no major difficulties can
be expected.
- Date
- 2008-01-22T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Consequences of inconsistency in formal logic: doesn’t that ruin the Semantic Web?
- Answer
- The new logo has been created as a high level image to represent the Semantic Web,
and the technology buttons have been designed to create consistent branding for all
of the standards that make up the Semantic Web. Going forwards we are planning to
create pictograms for the standards for t-shirts, mugs, etc. In that context, you'll
be seeing the familiar blue RDF triple again.
- Date
- 2007-10-21T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Why has W3C developed the new cube logo?
- Answer
-
The Semantic Web is about a web of data. The data itself can reside in databases,
spreadsheets, Wiki pages, or indeed traditional web pages.
The challenge is to develop tools that can “export” these data into RDF form:
RDF plays the role of a common model, as a kind of a “glue” to integrate the data.
That does not mean that the data must be physically converted into RDF form and stored
in, say, RDF/XML. Instead, automatic procedures, for example SQL to RDF converters
for relational databases, GRDDL processors for XHTML files with microformats, RDFa,
etc, can produce RDF data on-the-fly as an answer to, eg, queries. RDF data may also
be included in the data via other tools (e.g, Adobe’s XMP data that gets automatically
added to JPEG images by Photoshop). Authoring tools also exist to develop, eg, ontologies
on a high level instead of editing the ontology files directly. Of course, direct
editing of RDF data is sometimes necessary, but it can be expected to become less
and less prevalent as smarter editors come to the fore.
Clearly, lots of development is still to be done in this area, and it is a subject
of active Research and Development. The goal is to reuse, as much as possible, existing
data in its existing form, and minimize the RDF data that has to be created manually.
Note that, in fall 2009, W3C has started a Working Group, called RDB2RDF WG, that
aims at standardizing the description on how relational database data should be converted
into RDF. First results of that group are expected in early 2010.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Does the Semantic Web require me to manually markup all the existing web-pages, or
to convert all the data in relational databases into RDF?
- Answer
-
The issue, referred to by this question, is that different people will not agree
on exactly how to define all concepts. Eg, while most people have a fairly standard
concept of a “dog” or a “cat”, not everyone can distinguish between a “scalar” and
a “vector”, for instance. Any computer application which tries to standardize its
ontology will necessarily distort what at least some people are really trying to express;
as a consequence, there will be ontological mismatches across parts of the Web designed
by different people. The issue is whether this may not ruin the very goals of the
Semantic Web.
However, the Semantic Web does not rely on having one, big, all-encompassing
ontology. Instead, the Semantic Web is built up from small like-minded communities
that can find agreement on terms amongst themselves. Applications, then, can and
do interact without attempting to achieve global consensus. There is no requirement
for global ontologies: instead, an application need only map the terms relevant for
a particular transaction into a common vocabulary. Of course, though agreement need
only be local, adoption of existing vocabularies facilitates data sharing and integration.
Note that this issue is, essentially, the same as the one asking whether the
Semantic Web requires everybody to subscribe to a single, predefined, giant ontology;
see also the answer to that question, including further examples.
- Date
- 2008-01-22T00:00+00:00
- InGroup
- TechieQuestions
- Question
- People will never get common agreement on terms; won’t this lead to the failure of
the Semantic Web?
- Answer
-
No formal definitions, but of course there are different approaches. Indeed, the
complexity and variety of applications referring to the Semantic Web is increasing
every day, which means that various application areas, implementers, developers, etc,
would emphasize different aspects of Semantic Web technologies. This wide range of
applications include data integration, knowledge representation and analysis, cataloguing
services, improving search algorithms and methods, social networks, etc.
- Date
- 2008-06-27T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- Are there any other definitions or thought of Semantic Web, if any?
- Answer
-
There are a number of conference series that are either dedicated to the Semantic
Web or which always have a significant Semantic Web track. The best known are:
The “International Semantic Web Conference” series is a yearly event that publishes
its proceedings by Springer (the proceedings are online since 2006). While these conferences
typically circulate around the globe, the “European Semantic Web Conference” and the
“Asian Semantic Web Conference” series are held somewhere in Europe, respectively
in Asia.
The “International World Wide Web
Conference” is a major yearly conference on World Wide Web Technologies in general,
which always has a strong Semantic Web track both for the academic and the developers’
communities. Look at the page of the organizing committee for further details on these
conferences and links to their proceedings.
The yearly Semantic Technologies conference has also become a major event. It
is less focussed on the research aspects of the Semantic Web but concentrates rather
on the industrial, business aspects, new applications and developments.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Where can I find papers/publications about the Semantic Web?
- Answer
-
The Semantic Web provides an application framework that extends the current Web,
does not replace it. That also means that the current infrastructure of firewalls,
various levels of protections, encryption, etc, remain in place. If, for whatever
reason (privacy, business, etc), the data should be kept behind the firewall on the
Intranet, rather than being in the open, this just means that that particular Semantic
Web application operates on the Intranet. This is not unlike the development of the
traditional Web, the usage of Web Services, etc: a number of applications were developed
to be used behind corporate firewalls; some of them migrated later to the full Web,
some other stayed behind the firewall. The same is valid for Semantic Web applications.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Does the Semantic Web require me to put all my data into the public domain? What about
my sensitive data?
- Answer
-
The current, standardized version of SPARQL deals only with retrieving selected
data from RDF graphs. There is no equivalent of the SQL INSERT, UPDATE, or DELETE
statements. Most RDF-based applications handle new, changing, and stale data directly
via the APIs provided by specific RDF storage systems. Alternatively, RDF data can
exist virtually (i.e. created on-demand in response to a SPARQL query). Also, there
are systems which create RDF data from other forms of markup, such as Wiki markup
or the Atom Syndication Format.
However, there is indeed demand to cover this functionality, too. The
SPARQL Working Group is currently active in developing a new version of SPARQL,
and this will include these facilities, too. A first, draft version of the SPARQL
1.1 Update document is already available.
- Date
- 2008-02-11T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Can I use SPARQL to insert, delete, or update RDF data?
- Answer
-
The GRDDL provides a “bridge” to the microformats approach while RDFa provides
an XHTML1.1 module that gives the possibility to use virtually any RDF vocabulary
as annotations of the XHTML content, yielding RDF data. Both approaches can be used.
- Date
- 2008-06-27T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- How do I put RDF into my (X)HTML Pages?
- Answer
-
Some parts of the Semantic Web technologies are based on results of Artificial
Intelligence research, like knowledge representation (e.g., for ontologies or rules),
model theory (e.g., for the precise semantics of RDF and RDF Schemas), or various
types of logics (e.g., for rules). However, it must be noted that Artificial Intelligence
has a number of research areas (e.g., image recognition) that are completely orthogonal
to the Semantic Web.
It is also true that the development of the Semantic Web brought some new perspectives
to the Artificial Intelligence community: the “Web effect”, i.e., the merge of knowledge
coming from different sources, usage of URIs, the necessity to reason with incomplete
data; etc.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … Artificial Intelligence?
- Answer
-
Description Logic is the mathematical theory (stemming from knowledge representation)
that is at the basis of some of the technologies defined on the Semantic Web, like
the so-called “Direct Semantics” of OWL (loosely referred to as OWL-DL).
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … Description Logic?
- Answer
-
The meta and link elements in HTML can be used to add metadata to an HTML page.
In Semantic Web terms, this is equivalent to the process of defining RDF relationships
for that page as a “source”. Note, however, that these elements can be used to define
relationships for the enclosing HTML file only, whereas the Semantic Web allows the
definition of relationships on any resource on the Web. That also means that the meta
and link elements can be used by the author of the document only, whereas, on the
Semantic Web, anybody could publish metadata concerning that page. GRDDL allows easy
and automatic extraction of meta header data, such as that given by Dublin Core, to
RDF.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … HTML meta headers?
- Answer
-
Both formalisms have their strengths and weaknesses; their area of usage is different.
The two data models serve different constituencies and the choice really depends on
the application. There is no better or worse; only different.
One of XML’s strengths is its ability to describe strict hierarchies. Applications
may rely on and indeed exploit the position of an element in a hierarchy: for example,
most browsers provide a different rendering of HTML’s li element depending on how
“deep” the enclosing list is. XML makes it easy to control the content via XML Schemas
and combine XML data that abide to the same Schema or DTD.
However, combining different XML hierarchies (technically, DOM trees) within
the same application may become very complex. XML is not an easy tool for data integration.
On the other hand, RDF consists of a very loose set of relations (triples). Due to
its usage of URIs it is very easy to seamlessly merge triple sets, ie, data described
in RDF within the same application; it is therefore ideal for the integration of possibly
heterogenous information on the Web. But this has its price: reconstructing hierarchies
from RDF may become quite complex. As an example, it would be fairly complicated (and
unnecessary) to describe, eg, vector graphics, using RDF; use SVG instead!
RDF based vocabularies, and the accompanying semantic formalisms like RDFS or
OWL, also make it easy to define inference possibilities on RDF data. Although this
could be done around XML dialects, too, it would remain application specific and not
portable.
For existing XML-based vocabularies, one can develop an GRDDL transformation
to RDF using a language such as XSLT and then use the power of RDF to merge your pre-existing
XML formats. For new vocabularies, this technique allows you to use both XML and RDF-based
versions of your vocabulary, gaining the advantages of both.
- Date
- 2008-01-31T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … XML? When should I use RDF and when should I use XML?
- Answer
-
This issue is also related to the issue of using XML or RDF, addressed in a previous
question. First of all, let us quote from the OWL Guide recommendation:
An ontology differs from an XML Schema in that it is a knowledge representation,
not a message format. Most industry based Web standards consist of a combination of
message formats and protocol specifications. These formats have been given an operational
semantics, such as, “Upon receipt of this PurchaseOrder message, transfer Amount dollars
from AccountFrom to AccountTo and ship Product.” But the specification is not designed
to support reasoning outside the transaction context. For example, we won’t in general
have a mechanism to conclude that because the Product is a type of Chardonnay it must
also be a white wine.
One advantage of OWL ontologies will be the availability of tools that can reason
about them. Tools will provide generic support that is not specific to the particular
subject domain, which would be the case if one were to build a system to reason about
a specific industry-standard XML schema. […] They will benefit from third party tools
based on the formal properties of the OWL language, tools that will deliver an assortment
of capabilities that most organizations would be hard pressed to duplicate.
Also, XML data is very sensitive to the XML Schema it refers to. If the XML Schema
changes, the same XML data may become invalid, i.e., being rejected by Schema-aware
parsers. Somewhat similar dependence on RDF Schemas and Ontologies exist for RDF data,
too: if the RDF Schema or OWL Ontology changes, the inferences drawn from the RDF
data may change. However, the core RDF data is still usable, there is no notion of
the data being “rejected” by, e.g., a parser due to a Schema/Ontology change. In general,
RDF is more robust against changing of Schemas and Ontologies than XML is versus Schemas.
Note that a GRDDL transformation from XML to RDF may be given by an XML Schema as
described in the GRDDL specification. This allows any XML document that validates
according to the XML Schema given at the namespace URI of the XML vocabulary to be
converted to RDF.
- Date
- 2008-01-31T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … XML Schemas? What do ontologies buy me that XML and XML Schema don't?
- Answer
-
The Semantic Web is an extension of the current Web and not its replacement.
Islands of RDF and possibly related ontologies can be developed incrementally. Major
application areas (like Health Care and Life Sciences) may choose to “locally” adopt
Semantic Web technologies, and this can then spread over the Web in general. In other
words, one should not think in terms of “rebuilding” the Web.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- How is the Semantic Web related to the existing Web?
- Answer
-
There are a number of open source tools; see the W3C Wiki page for a few examples.
These tools typically have their own languages for defining the mapping between the
database to RDF. W3C has started work on defining standards in this area in September
2009, done by the RDB2RDF Working Group.
In general, methods exist to convert RDF queries (e.g., in SPARQL) into SQL queries
on-the-fly; ie, the RDB looks like an RDF store when queried by an RDF tool. The details
of the mapping from Relational Tables to RDF notions is usually described for a specific
database using either a small ontology and/or a set of rules; this is the only manual
information to be generated for the conversion.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- How do I export my data from a Relational Database?
- Answer
-
Microformats are usually relatively small and simple sets of terms agreed upon
by a community. Data models developed within the framework of the Semantic Web have
the potential to be more expressive, rigorous, and formal (and are usually larger).
Both can be used to express structured data within web pages. In some cases, microformats
are appropriate because the extra features provided by Semantic Web technologies are
not necessary. Other cases requiring more rigor will not be able to use microformats.
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 property="dc:date" content 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.
GRDDL is a “bridge” to the microformats approach; it defines a general procedure
whereby microformats stored in an XHTML file can be transformed into RDF on–the–fly.
A list of microformat to RDF vocabulary can be found on on the ESW Wiki. Another technology
is RDFa that defines an XHTML1.1 module giving the possibility to use virtually any
RDF vocabulary as annotations of the XHTML content; a bit like microformats with somewhat
more rigor and a better way of integrating different vocabularies within the same
document. There is also an ongoing work to adapt RDFa to the upcoming HTML version,
HTML5.
- Date
- 2008-01-31T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … microformats
- Answer
-
Tagging has emerged as a popular method of categorizing content. Users are allowed
to attach arbitrary strings to their data items (for example, blog entries and photographs).
While tagging is easy and useful, it often discards a lot of the semantics of the
data. A folksonomy tag is typically 2/3 of an RDF triple. The subject is known: e.g.,
the URL for the flickr image being tagged, or the URL being bookmarked in delicious.
The object is known: e.g., http://flickr.com/photos/tags/cats or http://del.icio.us/tag/cats.
But the predicate to connect them is often missing. Machine-tags lend themselves to
RDF more since they better capture the relationship between the subject and the object.
Folksonomy providers are encouraged to capture or infer the semantics around their
tags and to leverage semantic web technologies such as RDF and SKOS to publish machine
readable versions of their concept schemes.
Another issue arising with tags is that the number of different tags meaning
the same things but differing in spelling, lower or upper case, usage of space or
underscore characters etc., may create major obstacles to them being used on a larger
scale. There are a number of initiatives, start-up companies, projects, etc., that
aim at combining the two approaches, providing a little bit of extra rigour using
Semantic Web techniques to create new type of applications (Reuters’ Open Calais service,
Radar Networks’ Twine, the MOAT initiative, Common Tag, etc.).
- Date
- 2007-11-27T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … tagging, folksonomies
- Answer
-
One aspect of Web 2.0, beyond the exciting new interfaces and the usage of a
common intelligence, is that it pushes intelligence and active agents from the server
to the client, more specifically the browser. Development of active client-side application
also means that these applications use all kinds of data; data that are on the Web
somewhere, or data that is embedded in the page though not necessarily visible on
the screen. Examples are microformats type annotation of the page, calendar data on
the Web, tagged images or links stored on a web site, etc. This aspect of Web 2.0,
ie, that applications are based on combining various types of data (“mashing up” the
data) that are spread all around on the Web coincides with the very essence of the
Semantic Web. What the Semantic Web provides is a more consistent model and tools
for the definition and the usage of qualified relationships among data on the Web.
I.e., both technologies focus on intelligent data sharing. A number of typical Web 2.0
demonstrations and applications emerge that, in the background, use Semantic Web tools
combined with AJAX and other, exciting user interface approaches.
In many cases, using RDF-based techniques makes the mashing up process easier,
mainly when data collected by one application is reused by another one somewhere down
the line. The general nature of RDF makes this “mashup chaining” straightforward,
which is not always the case for simpler Web 2.0 applications.
Trying to present these two approaches as alternatives, or even claiming folksonomies
to be superior to the Semantic Web approach, has been a topic of the blogosphere and
various publications for a while, but both communities realize these days that these
two techniques are complementary rather than competitive.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- HowDoesTheSWRelatesTo
- Question
- … Web 2.0?
- Answer
-
First of all, the question arises whether it is possible to use these two technologies
together. The answer is yes. One of the six recommendation track documents of RIF
is called “RIF RDF and OWL Compatibility”. In layman’s term, what it describes is
how the two “sides”, i.e., the rule and the classification sides, should work together
on the same data set. It defines some sort of an interplay between two different mechanisms:
the, shall we say, logic programming part and the knowledge representation part. Implementations
doing both are a bit like hybrid cars: they have two parallel engines and a well defined
connections between those two. That said, the document only defines what the combination
means; whether, for example, engines will always succeed in handling the two worlds
together in a finite time is not necessarily guaranteed in all cases. But we can be
positive: in many cases (ie, by accepting restrictions here and there) this combination
does work well, and there are, actually, good implementations out there that do just
that.
The substantive differences is that RIF (i.e., logic programming) and OWL are
designed to allow for optimizations of different sets of problems. Very broadly speaking,
OWL optimizes for taxonomic reasoning problems within an ontology specification (i.e.,
without the data), and logic programs optimize for reasoning problems within the data
(i.e., without the ontology). So a reasonable rule of thumb is, if one’s ontology
is very large one should probably use OWL, and if data set is very large, one should
probably use RIF. That being said, the expressive differences are quite minor, and
it very often boils down to personal experience and taste: some feel more comfortable
using rules while others prefer knowledge representation.
- Date
- 2007-05-15T00:00+00:00
- InGroup
- TechieQuestions
- Question
- How do I know when to use OWL and when to Rules? How can I use them both together?
- Title
- Semantically-Interlinked Online Communities
- Answer
-
You can have a human-readable display of RDF data by using RDF data browsers
like the Tabulator, Disco, Sig.ma, VisiNav, or the OpenLink RDF Browser, and web browser
extensions like the Semantic Radar. 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.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Can I see Semantic Web data directly in my browser?
- Answer
-
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 serializations) 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.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What formats can RDF be represented in?
- Answer
-
The Simple Knowledge Organization System (SKOS) is an ontology for expressing
the basic structure and content of concept schemes such as thesauri, classification
schemes, subject heading lists, taxonomies, glossaries, folksonomies, other types
of controlled vocabularies. It provides a standard, low-cost way of migrating existing
concept schemes to the Semantic Web, so that they can be used as-is for the development
of lightweight Semantic Web applications. SKOS is increasingly seen as a bridging
technology, providing the missing link between the rigorous logical formalism of ontology
languages such as OWL and the chaotic, informal and weakly-structured world of social
approaches to information management, as exemplified by social tagging applications.
- Date
- 2007-11-27T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What is SKOS?
- Answer
-
SPARQL users have asked for many extensions to the SPARQL query language. Some
of these have been accomodated by SPARQL implementations. In an attempt to inform
SPARQL users and to minimize implementation differences of non-standard SPARQL features
a new SPARQL Working Group has been set up early 2009. This group is busy defining
the minimal number of extensions that can be done without backward incompatibilities
and do not require a too large addition to the initial version of SPARQL. The first
drafts have been published in October 2009 and the work is planned to be completed
(resulting in an updated version of SPARQL, currently called SPARQL 1.1) by the end
of 2010.
- Date
- 2009-04-28T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Will there be a SPARQL “Next”? When will feature X be standardized?
- Answer
- The Semantic Web Activity at W3C groups together all the Working and Interest Groups
whose goals are to improve the current Semantic Web technologies or to contribute
to their wider adoption. The activity home page gives an up-to-date list of the current
work at W3C.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- What is the Semantic Web activity at W3C?
- Answer
-
The Semantic Web is a Web of data. There is a lot of data we all use every day,
and it's not part of the Web. For example, I can see my bank statements on the web,
and my photographs, and I can see my appointments in a calendar. But can I see my
photos in a calendar to see what I was doing when I took them? Can I see bank statement
lines in a calendar? Why not? Because we don't have a web of data. Because data is
controlled by applications, and each application keeps it to itself.
The vision of the Semantic Web is to extend principles of the Web from documents
to data. Data should be accessed using the general Web architecture using, e.g., URI-s;
data should be related to one another just as documents (or portions of documents)
are already. This also means creation of a common framework that allows data to be
shared and reused across application, enterprise, and community boundaries, to be
processed automatically by tools as well as manually, including revealing possible
new relationships among pieces of data.
Semantic Web technologies can be used in a variety of application areas; for example:
in data integration, whereby data in various locations and various formats can be
integrated in one, seamless application; in resource discovery and classification
to provide better, domain specific search engine capabilities; in cataloging for describing
the content and content relationships available at a particular Web site, page, or
digital library; by intelligent software agents to facilitate knowledge sharing and
exchange; in content rating; in describing collections of pages that represent a single
logical “document”; for describing intellectual property rights of Web pages (see,
eg, the Creative Commons), and in many others. The list of Semantic Web Case Studies
and Use Cases gives some further examples.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- How would you define the main goals of the Semantic Web?
- Answer
-
Not necessarily, at least not directly. The Semantic Web technologies may act
behind the scenes, resulting in a better user experience, rather than directly influencing
the “look” on the browser. This is already happening: there are Web Sites (e.g., Sun’s
white paper collection site, or Nokia’s support portal for their S60 series device,
Oracle’s virtual press room, Harper’s online magazine, or Yahoo!’s Finance portal)
that use Semantic Web technologies in the background.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- Will I “see” the Semantic Web in my everyday browser?
- Label
- Questions on RDF, Ontologies, SPARQL, Rules…
- Answer
-
In general most of the tools are of a good quality already. On the open source
domain Jena, Sesame, or Redland, for example, can easily be compared to xerces in
their widespread usage and richness of features; databases like Mulgara, AllegroGraph,
or Virtuoso are also in widespread use and have undergone a very thorough development
in the past few years. There are more and more commercial tools, including editors,
professional databases, content management systems, ontology creation and validation
tools, etc. The Wiki page on the W3C ESW Wiki site gives a good overview of most of
those.
Obviously, there is room for improvement. SW is a younger technology than XML
and it still needs time to catch up and have tools of the same maturity and efficiency
level than the XML World. However, huge improvements have already been made in the
past few years in all areas, and large-scale enterprise deployment is also happening
already. In general: availability of tools is not a reason any more for not developing
Semantic Web applications…
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Are the SW tools as robust and as ubiquitous as, say, the xerces XML parser?
- Answer
-
There are several lists on the Web that give a more-or-less comprehensive overview
of the various available tools. There is a Wiki page on the W3C ESW Wiki site that
is maintained by the W3C staff as well as the community at large. This page includes
references to programming environments, validators that can be used to validate RDF/XML
data or OWL ontologies, SPARQL endpoints, specialized editors or triple databases.
It also includes references to other lists.
- Date
- 2007-04-17T00:00+00:00
- InGroup
- HowDoIParticipate
- Question
- Where do I find tools for Semantic Web development?
- Answer
-
The Semantic Web standards follow the design principles of the Web in order to
allow the growth of a planet-wide collection of semantically-rich data. The key element
of this design is the use of Web addresses (URIs) to name things. Because the meaning
of a term in a language without central control becomes established by its consistent
use to achieve the same effect, and URIs are used around the World to access web pages,
the Web is used to establish globally-shared meaning for URIs in the Semantic Web.
(This is what people mean when they say RDF URIs are “grounded” in the Web.)
As with the Web in general, this approach allows the Semantic Web to grow and
evolve without any central control or authority, but while still maintaining as much
consistency and authorial control as needed for particular applications or particular
enterprises. The techniques for doing all this are still evolving, but ideally whenever
anyone sees a Semantic Web URI they can use it in their browser and see authoritative
documentation about its use. Moreover, whenever some software encounters a URI in
a Semantic Web context, it can dereference it and find an ontology which precisely
specifies how the term is related to other terms. The software may thus learn and
exploit new terms which are synonymous with terms it already knows, or related in
more complex and useful (but logically precise) ways.
All this results in the ability to find and correctly merge data from multiple
sources, sometimes even when they are provided with different ontologies.
“In the Semantic Web, it is not the Semantic which is new, it is the Web which
is new” Chris Welty, IBM
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Where is the “Web” in the Semantic Web?
- Label
- What is the Semantic Web?
- Answer
-
In order to achieve the goals described above, the most important is to be able
to define and describe the relations among data (i.e., resources) on the Web. This
is not unlike the usage of hyperlinks on the current Web that connect the current
page with another one: the hyperlinks defines a relationship between the current page
and the target. One major difference is that, on the Semantic Web, such relationships
can be established between any two resources, there is no notion of “current” page.
Another major difference is that the relationship (i.e, the link) itself is named,
whereas the link used by a human on the (traditional) Web is not and their role is
deduced by the human reader. The definition of those relations allow for a better
and automatic interchange of data. RDF, which is one of the fundamental building blocks
of the Semantic Web, gives a formal definition for that interchange.
On that basis, additional building blocks are built around this central notion.
Some examples are:
Tools to query information described through such relationships (eg, SPARQL)
Tools to have a finer and more detailed classification and characterization of
those relationships as well as the resources being characterized. This ensures interoperability,
more complex automatic behaviors. For example, a community can agree what name to
use for a relationship connecting a page to one’s calendar; this name can then be
used by a large number of users and applications without the necessity to redefine
such names every time.
(E.g., RDF Schemas, OWL, SKOS)
For more complex cases, tools are available to define logical relationships among
resources and their relationships (for example, if a relationships binds a person
to his/her email address, it is feasible to declare that the email address is unique,
ie, the address is not shared by several persons). Tools based on this level (e.g.,
OWL, Rules) can ensure more interoperability, can reveal inconsistencies and find
new relationships.
Tools to extract from, and to bind to traditional data sources to ensure their
interchange with data from other sources. (E.g., GRDDL, RDFa, POWDER)
- Date
- 2007-04-17T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- What are the major building blocks of the Semantic Web?
- Answer
-
It is difficult to predict what a “killer application” is for a specific technology,
and the prediction is often erroneous. That said, the integration of currently unbound
and independent “silos” of data in a coherent application is certainly a good candidate.
Specific examples are currently explored in areas like Health Care and Life Sciences,
Public Administration, Engineering, etc.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- WhatIsTheSW
- Question
- What is the “killer application” for the Semantic Web?
- Answer
-
Obviously, that would not be feasible. If ontologies are used, they can come
from anywhere and be mixed freely. In fact the “ethos” of the Semantic Web is to share
and reuse as much as possible, and lot of work is done to semi-automatically bridge
different vocabularies. Typical Semantic Web applications mix ontologies developed
by different communities on the Web, like the Dublin Core metadata, FOAF (friend-of-a-friend)
terms, etc.
The Semantic Web’s attitude to ontologies is no more than a rationalization
of actual data-sharing practice. Applications can and do interact without achieving
or attempting to achieve global consistency and coverage. A system that presents a
retailer’s wares to customers will harvest information from suppliers’ databases (themselves
likely to use heterogeneous formats) and map it onto the retailer’s preferred data
format for re-presentation. Automatic tax return software takes bank data, in the
bank’s preferred format, and maps them onto the tax form. There is no requirement
for global ontologies here. There isn’t even a requirement for agreement or global
translations between the specific ontologies being used except in the subset of terms
relevant for the particular transaction. Agreement need only be local, but adoption
of vocabularies from existing ontologies facilitates data sharing and integration.
Of course, some of the vocabularies may become more and more widely used and adopted,
but the evolution is more bottom-up, rather than top-down.
- Date
- 2008-01-22T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Does the Semantic Web require everybody to subscribe to a single, predefined, giant
ontology?
- Answer
-
Broadly speaking, inference on the Semantic Web can be characterized by discovering
new relationships. As described elsewhere in this FAQ, the data is modeled as a set
of (named) relationships between resources. “Inference” means that automatic procedures
can generate new relationships based on the data and based on some additional information
in the form of an ontology or a set of rules. Whether the new relationships are explicitly
added to the set of data, or are returned at query time, is simply an implementation
issue.
A simple example may help. The data set to be considered may include the relationship
(Flipper isA Dolphin). An ontology may declare that “every Dolphin is also a Mammal”.
That means that a Semantic Web program understanding the notion of “X is also Y” can
add to the set of relationships the statement (Flipper isA Mammal), although that
was not part of the original data. One can also say that the new relationship was
“discovered”.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What is “inference” on the Semantic Web?
- Answer
-
It depends on the application. The answer on the role of ontologies and/or rules
includes a very simple ontology example. Some applications may decide not to use even
such small ontologies, and rely on the logic of the application program. Some application
may choose to use very simple ontologies like the one described, and let a general
Semantic Web environment use that extra information to make the identification of
the terms. Some applications need an agreement on common terminologies, without any
rigor imposed by a logic system. Finally, some applications may need more complex
ontologies with complex reasoning procedures. It all depends on the requirements and
the goals of the applications.
The current Semantic Web technologies offer a large palette of languages to
describe simple or complex terminologies: RDF Schemas, SKOS, RIF or various dialects/profiles
of OWL (OWL DL, OWL 2 QL, OWL 2 EL, OWL 2 RL, OWL Full). These technologies differ
in expressiveness but also in complexity. Applications have a choice along a range
from RDF Schema for representing the simplest ontology level, to OWL Full for maximum
expressiveness. In addition semantic web users are encouraged to leverage existing
ontologies where possible: e.g., SKOS for representing basic structures like thesauri,
taxonomies or other controlled vocabularies. Good places to look for existing ontologies
are detailed elsewhere in this FAQ. They also have a choice of not to use any of those;
the usage of ontologies is not a requirement for Semantic Web applications.
- Date
- 2008-02-14T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Must I use ontologies for Semantic Web Applications?
- Answer
-
Ontologies define the concepts and relationships used to describe and represent
an area of knowledge. Ontologies are used to classify the terms used in a particular
application, characterize possible relationships, and define possible constraints
on using those relationships. In practice, ontologies can be very complex (with several
thousands of terms) or very simple (describing one or two concepts only).
An example for the role of ontologies or rules on the Semantic Web is to help
data integration when, for example, ambiguities may exist on the terms used in the
different data sets, or when a bit of extra knowledge may lead to the discovery of
new relationships.
A general example may help. A bookseller may want to integrate data coming from
different publishers. The data can be imported into a common RDF model, eg, by using
converters to the publishers’ databases. However, one database may use the term “author”,
whereas the other may use the term “creator”. To make the integration complete, and
extra “glue” should be added to the RDF data, describing the fact that the relationship
described as “author” is the same as “creator”. This extra piece of information is,
in fact, an ontology, albeit an extremely simple one.
Languages like RDF Schemas and various variants of OWL provide languages to express
ontologies in the Semantic Web context. These are stable specifications, published
in 2004, with an update of OWL (denoted by “OWL 2”) published 2009.
- Date
- 2007-05-15T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What are ontologies in the Semantic Web context?
- Answer
-
The real difficulty, when developing an ontology, is to understand the problem
that has to be modeled and find an agreement on a community level. RDF Schemas and/or
OWL provide a framework to formalize those ontologies in a specific language; the
time and energy needed to learn and use them is only a fraction of the time needed
to develop an ontology itself, ie, understand the terms and the relationships of given
area of knowledge and agree with your peers. Ontology development tools, like Protégé
or SWOOP, hide most of the syntax complexity and let the user concentrate on the real
representation issues.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What is involved in developing an ontology using Semantic Web technologies?
- Answer
-
On the Semantic Web both ontologies and rules are used to express extra constraints
and logical relationships among resources. An example for their usage is to help
data integration when, for example, different terms are used to describe the same
thing in different data sets, or when a bit of extra knowledge may lead to the discovery
of new relationships.
Ontologies and rules refer to two different traditions stemming from logic, as
developed in the past decades. Whereas ontologies are more closely related to classification
systems, and particularly to description logic, rules rely more on the advances of
logic programming and rule based systems.
See the separate questions on Ontologies and on Rules.
- Date
- 2007-05-15T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What role do ontologies and/or rules have on the Semantic Web?
- Answer
-
In general, ontologies should be created and maintained by various, specialized
communities. The preference of W3C is to let these other communities develop their
own ontologies; this is the case for well known ontologies like the Dublin Core, FOAF,
DOAP, etc.
There are cases, however, when ontologies are developed at W3C. This is the case
when, for example, another W3C technology needs its own, specialized ontology (EARL
is a good example), when W3C feels that the existence of a particular ontology is
crucial for the advancement of the Semantic Web, or when the community prefers to
use, for example, the facilities offered by the Incubator Activity of W3C.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Will W3C be standardizing any particular ontologies?
- Answer
-
Major datasets (or access to existing datasets) are created quite often these
days. Just some examples:
The DBpedia community effort to query Wikipedia like a database (see also a more
detailed blog entry on this project).
IngentaConnect bibliographic metadata (around 200 million triples)
RDF/OWL representation of Wordnet
eBusiness ontology for products and services: eClassOwl
the Gene Ontology, to describe gene and gene products attributes in any organisms
protein sequence and annotation data: UniProt
Geonames Ontology and associated RDF data: geographical features (e.g., information
on the city of Berlin) encoded in RDF
Whereas these are randomly chosen and individual examples, the “Linking Open
Data on the Semantic Web” community project aims not only at making various open data
sources available on the Web as RDF, but also to create links among the various data
sets, thereby creating a nucleus for a Web of Data. All data sets bound together by
this projects include billions of RDF triples, with millions of triples among the
various datasets.
- Date
- 2007-11-26T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Is there an uptake in public datasets for the Semantic Web? Are there major data published
for the Semantic Web already?
- Answer
-
The W3C Data Access Working Group has developed the SPARQL Query Language. SPARQL
defines queries in terms of graph patterns that are matched against the directed graph
representing the RDF data. SPARQL contains capabilities for querying required and
optional graph patterns along with their conjunctions and disjunctions. The result
of the match can also be used to construct new RDF graphs using separate graph patterns.
SPARQL can be used as part of a general programming environment, like Jena,
but queries can also be sent as messages to a remote SPARQL endpoints using the companion
technologies SPARQL Protocol and SPARQL Query Result in XML. Using such SPARQL endpoints,
applications can query remote RDF data and even construct new RDF graphs, without
any local processing or programming burden. For more questions on SPARQL, see also
the separate FAQ on SPARQL.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- How can I query RDF data?
- Answer
-
RDF—the Resource Description Framework—is a standard model for data interchange
on the Web. RDF has features that facilitate data merging even if the underlying schemas
differ, and it specifically supports the evolution of schemas over time without requiring
all the data consumers to be changed.
RDF extends the linking structure of the Web to use URIs to name the relationship
between things as well as the two ends of the link (this is usually referred to as
a “triple”). Using this simple model, it allows structured and semi-structured data
to be mixed, exposed, and shared across different applications.
This linking structure forms a directed, labelled graph, where the edges represent
the named link between two resources, represented by the graph nodes. This graph view
is the easiest possible mental model for RDF and is often used in easy-to-understand
visual explanations.
The “RDF Primer” is a good material for further reading on RDF.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What is RDF?
- Answer
-
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.
In fact, using GRDDL, a way to automate mappings from XML to RDF easily, many XML
vocabularies can be considered applications of RDF.
Note that one of the serialization formats of RDF is indeed based on XML (RDF/XML),
and this is probably the most widely used format today. But others exist, see the
separate question on RDF representation.
- Date
- 2008-01-31T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Isn’t RDF simply an XML application?
- Answer
-
The term “rules” in the context of the Semantic Web refers to elements of logic
programming and rule based systems bound to Semantic Web data. Rules offer a way to
express, for example, constraints on the relationships defined by by RDF, or may
be used to discover new, implicit relationships.
Various rule systems (production rules, Prolog-like systems, etc) are very different
from one another, and it is not possible to define one rule language to encompass
them all. However, it is possible to define a “core” that is essentially understood
by all rule systems. This core is based on restricted kind of rule, called a “Horn”
rule, which (like most rules) has the form “if conditions then consequence”, but it
places certain restrictions on the kinds of conditions and consequences that can
be used.
A general example may help. While integrating data coming from different sources,
the data may include references to persons, their name, homepage, email addresses,
etc. However, the data does not say when two persons should be considered as identical,
although this is clearly important for a full integration. An extra condition can
be expressed stating that “if two persons have similar names, home pages, and email
addresses, then they are identical”. Such condition can be naturally expressed with
Horn rules.
The Rule Interchange Format (RIF) Working Group is currently working on a precise
definition of this “core” Rule language, on ways to extend this rule language to various
variants (production rules, logic programming, etc), to exchange expression of rules
among systems, and to define the precise relationships of these rules with OWL ontologies
and their usage with RDF triples.
- Date
- 2007-05-15T00:00+00:00
- InGroup
- TechieQuestions
- Question
- What are rules on the Semantic Web?
- Answer
-
No. What the Semantic Web technologies do is to define the “language” with well
understood rules and internal semantics, ie, RDF Schemas, various dialects of OWL,
or SKOS. Which of those formalisms are used (if any) and what is “expressed” in those
language is entirely up to the applications. Ontologies may be developed by small
communities, from “below”, so to say, and shared with other communities.
- Date
- 2007-04-12T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Does the Semantic Web try to impose meaning from the top?
- Answer
-
SPARQL is a query language developed for the RDF data model; queries themselves
look and act like RDF. I.e., the queries are independent of the physical representation
of the RDF data (the structure of the databases, their representation in an RDF/XML
file, etc). If query was done via, for example, XQuery, the application would have
to know how that particular RDF data exactly represented as RDF/XML (and RDF/XML is
only one of the possible serialization of the RDF data).
- Date
- 2007-04-17T00:00+00:00
- InGroup
- TechieQuestions
- Question
- Why not use SQL and/or XQuery to query RDF data? Why develop yet another query language?
