What is the semantic web? [closed]

Question

I've heard a lot about the semantic web but I'm still not exactly sure what it is. How will it be different to the web we know now?

Answer 1

Currently with HTML pages we have markup tags which describe how content should be displayed, <b>, '<pre>, etc. These tags imply no meaning about their content.

The concept of a semantic web is that documents would contain XML tags that do imply meaning about their content. For example <person><firstname>. The grand idea is that CSS would be able to format documents such as these but it would also be possible to extract meaningful info easily from these documents.

Answer 2

The Semantic Web is at heart a really simple idea. (Like all the good ones.)

The Web at present consists of documents with links between them. Google have made a pretty good business out of using context, and anchor text within the links, to work out what the links mean and build an engine for retrieving data based on that. In other words, Google guesstimate what the semantic meaning of a link is.

The Semantic Web idea is "what if these links were typed?" Every fact on the Web gets an address - a URI - and is linked to other facts (also URIs) by relations (also URIs). Groups of relations are called "ontologies".

So instead of page A links to page B, like on the current web, links on the Semantic Web are more like:

URI A links to URI B with a link of type URI C.

Anything can have a URI. People can have URIs; usually we use a set of relations called FOAF to describe them. So let's say the URI for Jeff Atwood is http://codinghorror.com/foaf.xml; then you could say:

<http://codinghorror.com> <http://xmlns.com/foaf/0.1/homepage> <http://codinghorror.com/foaf.xml>

ie, http://codinghorror.com is the homepage of the person represented by the contents of http://codinghorror.com/foaf.xml.

Now machines can read, and query, these relationships - so you turn the Web into a database that computers can immediately do something with. The Semantic Web query language is SPARQL, and it's worth checking out.

Answer 3

The Semantic Web is just that - a Semantic (meaningful) layer on top of the WWW. It is semi structured (RDF), it is self-describing (ontologies using OWL), and allows resource discovery (SPARQL).

The Semantic Web works on the premise of the "Open World" assumption; just because something is not stated doesn't mean it doesn't exist, it is simply "unknown". This is a fundamentally different logic to that used in an RDBMS like MySQL et al. - if something is missing it doesn't exist - "Closed World" assumption. Prolog and DATALOG are good examples of Close World logics.

If you want to really learn what is happening underneath, you'll need to look at its foundations, which lie in Description Logic. A good overview of the Description Logic can be found here: http://www.inf.unibz.it/~franconi/dl/course/

If you want to learn more about RDF, read the RDF Primer. RDF Semantics is another rip-roaring read.

Researchers have basically given up on the "Semantic" part of the Semantic Web and decided to focus on Linked Data - how RDF triples can be navigated so that we can waste more Internet bandwidth ;-)

Answer 4

The Semantic Web is what Tim Berners-Lee, the inventor of the World Wide Web, really intended the Web to be—that is, a global graph of interlinked data. It is a generalization of a social graph, where you can use social data (with vocabularies like FOAF) as well as any other kind of machine-understandable data and connect them to each other. The standard formats for describing this infortmation to machines is the Resource Description Format (RDF) and the Web Ontology Language (OWL). There's already a lot of encoded data on the Web, including an RDF version of Wikipedia, called DBPedia.

The Semantic Web will be different than today's Web in that computers as well as humans will understand what documents contain as well as what the significance of the links between documents are. This will facilitate automation of information-processing tasks, including researching information from trustworthy sources. The full SemWeb stack includes cryptography, proof systems, and trust networks.

Answer 5

How will it be different to the web we know now?

Right now the HTML+CSS is centered more on structure and presentation. Semantics is about the meaning of the information. In semantic web you use shared ontologies to establish meaning (semantic) of the object and meaning of relations between the objects. Best known ontologies are: FOAF and Dublin Core.

Typically semantics would be expressed in specialized language, such as RDF or OWL. RDF can be embedded within XHTML using eRDF or W3C's RDFa.

Less structured alternative to eRDF/RDFa are microformats.

Read more at: http://en.wikipedia.org/wiki/Semantic_web

Answer 6

Semantic web is the only pragmatic solution proposed so far to repair inherent design flaws of World Wide Web. Because the designers of the internet, as we know it today, did not provide mechanisms which would address fundamental linguistic phenomenons which govern the way humans think and communicate such as homonymy, synonymy etc. searching for information on the internet results in a flood of false positives. The idea of semantic web boils down to assigning unequivocal identifiers to web resources which will help identify their meaning correctly. If it succeeds one day we may forget what the usual google search looked like, if it fails all will remain as it is now.