This link has been bookmarked by 178 people . It was first bookmarked on 28 Jun 2006, by Bob Ashley.
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05 May 12
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02 May 12
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale.
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Data that is geneally hidden away in HTML files is often useful in some contexts, but not in others.
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So the Semantic Web can be seen as a huge engineering solution... but it is more than that.
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as it becomes easier to publish data in a repurposable form, so more people will want to pubish data, and there will be a knock-on or domino effect.
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A URI is simply a Web identifier: like the strings starting with "http:" or "ftp:" that you often find on the World Wide Web
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25 Mar 12
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide Web, or as a globally linked database.
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Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web.
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So the Semantic Web can be seen as a huge engineering solution
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The Semantic Web is generally built on syntaxes which use URIs to represent data, usually in triples based structures: i.e. many triples of URI data that can be held in databases, or interchanged on the world Wide Web using a set of particular syntaxes developed especially for the task. These syntaxes are called "Resource Description Framework" syntaxes.
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28 Feb 12
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What Is The Semantic Web?
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e Sema
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The Power Of Semantic Web Languages
The main power of Semantic Web languages is that any one can create one, simply by publishing some RDF that describes a set of URIs, what they do, and how they should be used. We have already seen that RDF Schema and DAML are very powerful langauges for creating languages.
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13 Feb 12
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26 Jan 12
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07 Dec 11
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RDF XML is considered to be the standard interchange format for RDF on the Semantic Web, although it is not the only format. For example, Notation3 (which we shall be going through later on in this article) is an excellent plain text alternative serialization.
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Note that some people actually prefer using XML RDF to Notation3, but it is generally accepted that Notation3 is easier to use, and is of course convertable to XML RDF anyway.
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Screen scraping is the act of literally getting the data from a source into a more manageable form (i.e. RDF) using whatever means come to hand.
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However, screen scraping is often a tedious solution, so another way to approach it is to build proper RDF systems that take input from the user and then store it straight away in RDF.
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Notation3: RDF Made Easy
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_:a1 <http://xyz.org/#name> "Sean" .
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This may be read as "there is something that has the name Sean", or "a1 has the name Sean, for some value of a1". These things are called anonymous nodes, because they don't have a URI, and are sometimes referred to as
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existentially quantified nodes
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Although we won't be discussing inference engines until later on in this article, we should note at this point that much RDF and Semantic Web processing (albeit often only experimental or demonstrative, at this stage) is done using a Python program called CWM or "Closed World Machine". More information can be found on the SWAP site.
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Simple Data Modelling: Schemata
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The first three most important concepts that RDF and RDF Schema give us are the "Resource" (rdfs:Resource), the "Class" (rdfs:Class), and the "Property" (rdf:Property).
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RDF Schema also has a few more properties that we can make use of: rdfs:subClassOf and rdfs:subPropertyOf.
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The next concepts which RDF Schema provides us, which are important to mention, are ranges and domains. Ranges and domains let us say what classes the subject and object of each property must belong to. For example, we might want to say that the property ":bookTitle" must always apply to a book, and have a literal value:-
:Book rdf:type rdfs:Class . :bookTitle rdf:type rdf:Property . :bookTitle rdfs:domain :Book . :bookTitle rdfs:range rdfs:Literal . :MyBook rdf:type :Book . :MyBook :bookTitle "My Book" .
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Inference
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Indeed, this is already possible with Semantic Web tools that we have at our disposal today: CWM. Unfortunately, great levels of inference can only be provided using "First Order Predicate Logic" languages, and DAML is not a FOPL language entirely.
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For the Semantic Web to become expressive enough to help us in a wide range of situations, it will become necessary to construct a powerful logical language for making inferences. There is a raging debate as to how and even whether this can be accomplished, with people pointing out that RDF lacks the power to quantify, and that the scope of quantification is not well defined. Predicate logic is better discussed in John Sowa's excellent Mathematical Background (Predicate Logic).
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04 Oct 11
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27 Sep 11
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14 Sep 11
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06 Sep 11
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04 Aug 11
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15 Jul 11
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22 Jun 11
Ian GloverAn overview of the key technologies of the semantic web.
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11 May 11
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22 Mar 11
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sh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide
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17 Mar 11
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24 Feb 11
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04 Feb 11
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01 Feb 11
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28 Jan 11
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24 Jan 11
stefaan vande walleThis document is designed as being a simple but comprehensive introductory publication for anybody trying to get into the Semantic Web: from beginners through to long time hackers. Recommended pre-reading: the Semantic Web in Breadth.
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23 Jan 11
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Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web.
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hansdezwartThis document is designed as being a simple but comprehensive introductory publication for anybody trying to get into the Semantic Web: from beginners through to long time hackers. Recommended pre-reading: the Semantic Web in Breadth.
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22 Jan 11
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29 Dec 10
Dante-Gabryell MonsonThe Semantic Web is generally built on syntaxes which use URIs to represent data, usually in triples based structures: i.e. many triples of URI data that can be held in databases, or interchanged on the world Wide Web using a set of particular syntaxes de
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28 Dec 10
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27 Dec 10
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19 Oct 10
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08 Oct 10
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24 Sep 10
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20 Sep 10
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale
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Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web
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07 Sep 10
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10 Aug 10
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17 Jul 10
Kathleen Ackroyd"You can think of it as being an efficient way of representing data on the World Wide Web, or as a globally linked database."
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31 Mar 10
Amanda HenryUsed! and cited
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide Web, or as a globally linked database.
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06 Mar 10
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26 Oct 09
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18 Oct 09
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15 Oct 09
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17 Aug 09
bam bamAmbient Information and SEM\n\nThe scope of information was discussed a little, but let's take into consideration what it really means to have a "local" and a "global" system.\n\nIn general, there are small and large scale systems, and interactions between the two will most likely form a huge part of the transactions that occur on the Semantic Web. Let's define what we mean by large, medium, and small scale systems.\nLarge Scale\n\nAn example of a large scale system is two companies that are undergoing a merger needing to combine their databases. Another example would be search engines compiling results based upon a huge range of data. Large scale Semantic Web systems generally involve large databases, and heavy duty inference rules and processors are required to handle the databases.\nMedium Scale\n\nMedium scale Semantic Web systems attempt to make sense out of the larger scale Semantic Web systems, or are examples of small scale Semantic Web systems joined together. An example of the former is a company trying to partially understand two large scale invoice formats enough to use them together. An example of the latter is of two address book language groups trying to create a super-address book language.\nSmall Scale\n\nSmall scale Semantic Web systems are less widely discussed. By small scale Semantic Web systems, we mean languages that will be used primarily offline, or piles of data that will only be transferred with a limited scope, perhaps between friends, departments, or even two companies.\n\nSharing data on a local level is a very powerful example of how the Semantic Web can be useful in a myriad of situations. In the next section on evolution we shall be finding out how interactions between the different sized systems will form a key part of the Semantic Web.
web semantic semanticweb rdf xml semantic-web introduction semantic_web
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Ambient Information and SEM
The scope of information was discussed a little, but let's take into consideration what it really means to have a "local" and a "global" system.
In general, there are small and large scale systems, and interactions between the two will most likely form a huge part of the transactions that occur on the Semantic Web. Let's define what we mean by large, medium, and small scale systems.
Large Scale
An example of a large scale system is two companies that are undergoing a merger needing to combine their databases. Another example would be search engines compiling results based upon a huge range of data. Large scale Semantic Web systems generally involve large databases, and heavy duty inference rules and processors are required to handle the databases.
Medium Scale
Medium scale Semantic Web systems attempt to make sense out of the larger scale Semantic Web systems, or are examples of small scale Semantic Web systems joined together. An example of the former is a company trying to partially understand two large scale invoice formats enough to use them together. An example of the latter is of two address book language groups trying to create a super-address book language.
Small Scale
Small scale Semantic Web systems are less widely discussed. By small scale Semantic Web systems, we mean languages that will be used primarily offline, or piles of data that will only be transferred with a limited scope, perhaps between friends, departments, or even two companies.
Sharing data on a local level is a very powerful example of how the Semantic Web can be useful in a myriad of situations. In the next section on evolution we shall be finding out how interactions between the different sized systems will form a key part of the Semantic Web.
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24 Jul 09
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10 Jun 09
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25 May 09
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15 May 09
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11 May 09
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29 Jan 09
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26 Jan 09
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03 Nov 08
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George BradfordThis document is designed as being a simple but comprehensive introductory publication for anybody trying to get into the Semantic Web: from beginners through to long time hackers. Recommended pre-reading: the Semantic Web in Breadth.
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28 Oct 08
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16 Sep 08
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03 Sep 08
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26 Aug 08
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22 Aug 08
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23 Jul 08
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What's the rationale for such a system? Data that is geneally hidden away in HTML files is often useful in some contexts, but not in others. The problem with the majority of data on the Web that is in this form at the moment is that it is difficult to use on a large scale, because there is no global system for publishing data in such a way as it can be easily processed by anyone. For example, just think of information about local sports events, weather information, plane times, Major League Baseball statistics, and television guides... all of this information is presented by numerous sites, but all in HTML. The problem with that is that, is some contexts, it is difficult to use this data in the ways that one might want to do so.
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A language which utilises three URIs in such a way is called RDF
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A triple can simply be described as three URIs.
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is an excellent plain text alternative serialization.
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Notation3
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For the Semantic Web to reach its full potential, many people need to start publishing data as RDF.
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CWM: An XML RDF And Notation3 Inference Engine
Although we won't be discussing inference engines until later on in this article, we should note at this point that much RDF and Semantic Web processing (albeit often only experimental or demonstrative, at this stage) is done using a Python program called CWM or "Closed World Machine". More information can be found on the SWAP site.
At the moment, the best demonstration of its use can be how it can convert from XML RDF into Notation3 and vice versa. To convert "a.n3" into "a.rdf", simply use the following command line:-
python cwm.py a.n3 -rdf > a.rdf
CWM is a very powerful Semantic Web toolkit, and we shall be refering to it occasionally throught this article.
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13 Jun 08
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20 May 08
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01 May 08
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29 Apr 08
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24 Apr 08
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22 Apr 08
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20 Apr 08
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26 Mar 08
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide Web, or as a globally linked database.
-
Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web.
-
The problem with the majority of data on the Web that is in this form at the moment is that it is difficult to use on a large scale, because there is no global system for publishing data in such a way as it can be easily processed by anyone.
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The Semantic Web works on a principle of least power: the less rules, the better. This means that the Semantic Web is essentially very unconstraining in what it lets one say, and hence it follows that anyone can say anything about anything.
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[...] what we'll end up doing in the future is converting things, so for example [...] in the Semantic Web we will have a relationship between two langauges so that if you get an invoice in a langauge you don't understand, and you have... some business software which can pay invoices... by following links across the Semantic Web, your machine will be able to automatically convert it from one language to another, and so process it.- Tim Berners-Lee
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Where for example a library of congress schema talks of an "author", and a British Library talks of a "creator", a small bit of RDF would be able to say that for any person x and any resource y, if x is the (LoC) author of y, then x is the (BL) creator of y. This is the sort of rule which solves the evolvability problems. Where would a processor find it? [...]
- Semantic Web roadmap, Tim Berners-Lee
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23 Mar 08
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The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale.
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a globally linked database.
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A URI is simply a Web identifier:
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Notation3 is easier to use, and is of course convertable to XML RDF anyway.
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CWM is a very powerful Semantic Web toolkit
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great levels of inference can only be provided using "First Order Predicate Logic" languages, and DAML is not a FOPL language entirely
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The Semantic Web works on a principle of least power: the less rules, the better.
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14 Mar 08
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19 Feb 08
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06 Feb 08
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28 Nov 07
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29 Sep 07
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19 Sep 07
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13 Jun 07
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11 Jun 07
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05 Jun 07
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04 Jun 07
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why use RDF rather than XML?
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why use RDF rather than XML?
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do we use XML Schema in conjunction with RDF?
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sing XML Schema in conjunction with RDF may be useful for creating datatypes and so on. Therefore the answer is "possibly", with a caveat that it is not really used to control the syntax of RDF. This is a common misunderstanding, perpetuated for too long now.
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Screen scraping is the act of literally getting the data from a source into a more manageable form (i.e. RDF) using whatever means come to hand
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screen scraping is often a tedious solution, so another way to approach it is to build proper RDF systems that take input from the user and then store it straight away in RDF.
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The design criteria behind Notation3 were fairly simple: design a simple easy to learn scribblable RDF format, that is easy to parse and build larger applications on top of.
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_:a1 <http://xyz.org/#name> "Sean" .
This may be read as "there is something that has the name Sean", or "a1 has the name Sean, for some value of a1". These things are called anonymous nodes, because they don't have a URI, and are sometimes referred to as existentially quantified nodes.
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Note that it doesn't matter what alias you use for a URI, as long as you use the same one throughout that document.
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07 May 07
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04 May 07
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14 Apr 07
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13 Apr 07
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10 Mar 07
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06 Mar 07
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However, Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web.
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RDF Schema (also: RDF Schema Candidate Recommendation) was designed to be a simple datatyping model for RDF. Using RDF Schema, we can say that "Fido" is a type of "Dog", and that "Dog" is a sub class of animal. We can also create properties and classes, as well as doing some slightly more "advanced" stuff such as creating ranges and domains for properties.
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The first "layer" of the Semantic Web above the syntax discussed above is the simple datatyping model. A "schema" (plural "schemata") is simply a document or piece of code that controls a set of terms in another document or piece of code. It's like a master checklist, or definition grammar
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Notation3 a "poor-man's RDF authoring tool"
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literal values, simply enclose the value in double quote marks
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Note that it doesn't matter what alias you use for a URI, as long as you use the same one throughout that document. You can also declare many aliases
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giving parts of URIs aliases
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don't have a URI
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RFC 2396 as the general URI specification. The W3C maintains a list of URI schemes.
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anonymous nodes,
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If you don't want to give a URI for something that you are talking about, then there is a concept for that too (this is like saying "there is someone called... but without giving them a URI). You simply use an underscore and a colon, and then put a little label
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W3C have developed an XML serialization of RDF, the "Syntax" in the RDF Model and Syntax recommendation. RDF XML is considered to be the standard interchange format for RDF on the Semantic Web, although it is not the only format. For example, Notation3 (which we shall be going through later on in this article) is an excellent plain text alternative serialization.
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A triple can simply be described as three URIs >.
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Notation3 is easier to use, and is of course convertable to XML RDF anyway
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Screen scraping is the act of literally getting the data from a source into a more manageable form (i.e. RDF) using whatever means come to hand. Two useful tools for screen scraping are XSLT (an XML transformations language), and RegExps (in Perl, Python, and so on).
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In Notation3, we can simply write out the URIs in a triple, delimiting them with a "<" and " > > >" symbols.
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Note that a syntax was devised to be an even simpler subset of Notation3, called N-Triples, but it doesn't use prefixes, and hence many of the examples in this article are not valid N-Triples, but are valid Notation3.
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27 Feb 07
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07 Feb 07
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24 Jan 07
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23 Jan 07
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