Introduction to the semantic web

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http://www4.wiwiss.fu-berlin.de/bizer/pub/lod-datasets_2009-03-05_colored.pngSemantic web, you probably see diagrams that make no sense like this.

PREDICATES OWL CURIE TRIPLES SPARQL RDFLots & lots of confusing scary acronyms

Web 1.0 1993 Hyperlinks, static, consumptionIt’s worth going back in history. Web 1.0 was static. Publishers built things & people came & read them.

Web 2.0 2004 2 way, interactive, producing, socialWeb 2.0 - social web. People became the publishers, websites became the mechanism to allow people to connect (Flickr, Twitter,Facebook, Wikipedia).

Web 3.0 ~2010 Semantic, machine drivenWeb 3.0 - semantic, machine to machine, putting meaning behind the structure/content of websites.

What does semantic web mean. Lets say you do a search for a recipe on Google. Notice the search results, there’s reviews withstar ratings, there is ingredient facets, cooking time facets, kilojoule facets. How does this work?

Microdata, Microformats and RDFa. All methods of describing content and the relationships between content.

<a href=”http://creativecommons.org/licenses/by/3.0/”> <img src=”http://i.creativecommons.org/l/by/3.0/88x31.png”> </a>Let’s look at the basic HTML structure behind these mechanisms. Something every page has - license information. This istypically marked up like this as a link. There’s no meaning to the link, it could be a link to anywhere.

<a rel=”license” href=”http://creativecommons.org/licenses/by/3.0/”> <img src=”http://i.creativecommons.org/l/by/3.0/88x31.png”> </a>By adding in an attribute describing what the link is, suddenly we have turned the link from a normal link into something withsome semantic meaning. This is what all of these formats do, they add in extra descriptive markup.

schema.org A place that describes all the markup you can add for search engines (Google, Bing, Yahoo).

At this page you can see schemas for all sorts of common things - books, maps, music, photographs, recipies, reviews,scultpure, organisations, places and more.

<div xmlns:v="http://rdf.data-vocabulary.org/#" typeof="v:Recipe"> <h1 property="v:name">Grandmas Holiday Apple Pie</h1> <img src="apple-pie.jpg" rel="v:photo"/> By <span property="v:author">Carol Smith</span> Published: <span property="v:published" content="2009-11-05">November 5, 2009</span> <span property="v:summary">This is my grandmothers apple pie recipe. I like to add a dash of nutmeg.</span> <span rel="v:Review"> <span typeof="v:Review-aggregate"> <span rel="v:rating"> <span typeof="v:Rating"> <span property="v:average">4.0</span> stars based on <span property="v:count">35</span> reviews </span> </span> </span> </span> Prep time: <span property="v:prepTime" content="PT30M">30 min</span> Cook time: <span property="v:cookTime" content="PT1H">1 hour</span> Total time: <span property="v:totalTime" content="PT1H30M">1 hour 30 min< span> Yield: <span property="v:yield">1 9" pie (8 servings)</span> <span rel="v:nutrition"> <span typeof="v:Nutrition"> Serving size: <span property="v:servingSize">1 medium slice</span> Calories per serving: <span property="v:calories">250</span> Fat per serving: <span property="v:fat">12g</span>Let’s look at </span> the Google recipe example. This is marked up with RDFa. Don’t worry too much about the meanings the HTML of </span>yet as I’ll try to describe them all later. Ingredients:

<div xmlns:v="http://rdf.data-vocabulary.org/#" typeof="v:Recipe"> <h1 property="v:name">Grandmas Holiday Apple Pie</h1> <img src="apple-pie.jpg" rel="v:photo"/> By <span property="v:author">Carol Smith</span> Published: <span property="v:published" content="2009-11-05">November 5, 2009</span> <span property="v:summary">This is my grandmothers apple pie recipe. I like to add a dash of nutmeg.</span> <span rel="v:Review"> <span typeof="v:Review-aggregate"> <span rel="v:rating"> <span typeof="v:Rating"> <span property="v:average">4.0</span> stars based on <span property="v:count">35</span> reviews </span> </span> </span> </span> Prep time: <span property="v:prepTime" content="PT30M">30 min</span> Cook time: <span property="v:cookTime" content="PT1H">1 hour</span> Total time: <span property="v:totalTime" content="PT1H30M">1 hour 30 min< span> Yield: <span property="v:yield">1 9" pie (8 servings)</span> <span rel="v:nutrition"> <span typeof="v:Nutrition"> Serving size: <span property="v:servingSize">1 medium slice</span> Calories per serving: <span property="v:calories">250</span> Fat per serving: <span property="v:fat">12g</span>This deﬁnes </span>information about the content of the page. some basic </span> Ingredients:

<div xmlns:v="http://rdf.data-vocabulary.org/#" typeof="v:Recipe"> <h1 property="v:name">Grandmas Holiday Apple Pie</h1> <img src="apple-pie.jpg" rel="v:photo"/> By <span property="v:author">Carol Smith</span> Published: <span property="v:published" content="2009-11-05">November 5, 2009</span> <span property="v:summary">This is my grandmothers apple pie recipe. I like to add a dash of nutmeg.</span> <span rel="v:Review"> <span typeof="v:Review-aggregate"> <span rel="v:rating"> <span typeof="v:Rating"> <span property="v:average">4.0</span> stars based on <span property="v:count">35</span> reviews </span> </span> </span> </span> Prep time: <span property="v:prepTime" content="PT30M">30 min</span> Cook time: <span property="v:cookTime" content="PT1H">1 hour</span> Total time: <span property="v:totalTime" content="PT1H30M">1 hour 30 min< span> Yield: <span property="v:yield">1 9" pie (8 servings)</span> <span rel="v:nutrition"> <span typeof="v:Nutrition"> Serving size: <span property="v:servingSize">1 medium slice</span> Calories per serving: <span property="v:calories">250</span> Fat per serving: <span property="v:fat">12g</span> </span>This describes the star ratings </span> Ingredients:

<span property="v:count">35</span> reviews </span> </span> </span> </span> Prep time: <span property="v:prepTime" content="PT30M">30 min</span> Cook time: <span property="v:cookTime" content="PT1H">1 hour</span> Total time: <span property="v:totalTime" content="PT1H30M">1 hour 30 min< span> Yield: <span property="v:yield">1 9" pie (8 servings)</span> <span rel="v:nutrition"> <span typeof="v:Nutrition"> Serving size: <span property="v:servingSize">1 medium slice</span> Calories per serving: <span property="v:calories">250</span> Fat per serving: <span property="v:fat">12g</span> </span> </span> Ingredients: <span rel="v:ingredient"> <span typeof="v:Ingredient"> Thinly-sliced <span property="v:name">apples</span>: <span property="v:amount">6 cups</span> </span> </span> <span rel="v:ingredient"> <span typeof="v:Ingredient"> <span property="v:name">White sugar</span>: <span property="v:amount">3/4 cup</span> </span> </span> Further down it’s marked up with times, nutritional values, ingredients, etc. ...

So you can see from the markup, how Google can use this information to build the results page with the reviews, the facets fortime, ingredients and nutritional value. If those added bits of information weren’t added into the markup this couldn’t be built.Pages that have this extra markup in them tend to rank higher in Google that pages that don’t have this speciﬁc markup inthem.

Let’s enter into the world of the semantic web. Now there’s lots of scary terms when you start heading down this path - Triples,predicates, SPARQL. The basics really aren’t that scary, but immensely powerful. So let’s dive into the basics of RDFa.

R Resource D Description F Framework a attributesRDFa - RDF in attributes.

Frank HurleyLets start with a subject

Frank Hurley takesa predicate

Frank Hurley takes photographsand an object.

Subject Frank Hurley Predicate takes Object photographsThese three things make up a triple. with a subject, predicate & object.

Subject http://nla.gov.au/nla.pic-an25043941You have a subject - in this case the URL of the photo

Objects Exterior of.... -37.816068 144.961201 Museum http://nla.gov.au/nla.pic-an25043941 1961 1 negative : b&w ; 12.5 x 10.0 cm.You have objects that are related to the subject, but they are meaningless without...

Predicates Exterior of.... -37.816068 144.961201 Title Latitude Museum Longitude Coverage http://nla.gov.au/nla.pic-an25043941 Date Format 1961 1 negative : b&w ; 12.5 x 10.0 cm.Predicates. These form triples.

Finding namespacesOne of the beauties of this system is it’s supposed to be extensible, if there isn’t an existing namespace you can write your own(yuk). You can guarantee that 15 different organisations will write 15 different versions. We’ve seen this already in the examplesfrom schema.org, Dublin Core

CURIE dc:creator http://purl.org/dc/elements/1.1/creator The property called creator from the vocabulary identified by dcCompact URI’s called Curies.

dc:creator An entity primarily responsible for making the resource. Examples of a Creator include a person, an organization, or a service. Typically, the name of a Creator should be used to indicate the entity.It’s something that has a meaning & it’s something that should be being used consistently across all the cases that use it.

dc:title dc:creator dc:subject dc:coverage dc:relation dc:identifier dc:rights dc:type ...So we can ﬁll in the blanks for all of these bits of information

foaf:person foaf:knows foaf:isPrimaryTopicOfIn addition, we can also mark it up using other schemes, so people can be marked up with their relationships.

Let’s have a look at Flickr. With Flickr you can add tags, to help describe the image. If you add in tags in a special format theyare known as machine tags.

Now “machine tags” are a special type of tag. They actually start to describe the image & provide extra information. In this casegeo:lat= something geo:lon= something. However, they don’t actually link to a description, so although they copy, there isn’tquite the same degree of semantic structure to them.

In the library world we typically have a MARC record as our master record. Very ugly, but very structured. Fields with all theirarcane subﬁelds, each is deﬁned and has a distinct meaning.

We sometimes transpose that data into other formats. This is an export of our data from our OAI-PMH interface & you can seethat it’s in XML & it’s rich, everything has a value, it conforms to a standard structure - Dublin Core. Compared to MARC it’s a bitmore human readable.

We then take this information and present it on the web in HTML. But if we look at a web page, this rich markup is lost. In ourHTML we have basic markup that Gives a bit of weight to various parts of the page.

H1We have an H1 tag that gives some weight to the most important thing on the page - the title.

H1 TH TDWe mark up the rest of the information in a table. There’s an implied relationship between the table headings and the table data,but we’re not saying what that relationship is. It could be anything.

At a basic machine level, there really isn’t a lot that is describing these elements and there isn’t anything that makes thesespeciﬁc.

<div> <h1>[Sydney Harbour scene with naval vessels in foreground, and Harbour Bridge in distance] [picture] /</h1> <table> <tr> <th>Date</th> <td>[between 1910 and 1962]</td> </tr> <tr> <th>Format</th> <td>1 negative : acetate, b&w ; 8.7 x 12.1 cm.</td> </tr> <tr> <th>Online Versions</th> <td>http://nla.gov.au/nla.pic-an23417397</td> </tr> </table> </div>In this case it’s a table. there is an implicit relationship between the table header & the table data

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/ xhtml-rdfa-1.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:foaf="http://xmlns.com/foaf/0.1/"> <div about="http://nla.gov.au/nla.pic-an23417397"> <h1>[Sydney Harbour scene with naval vessels in foreground, and Harbour Bridge in distance] [picture] /</h1> <table> <tr> <th>Date</th> <td>[between 1910 and 1962]</td> </tr> <tr> <th>Format</th> <td>1 negative : acetate, b&w ; 8.7 x 12.1 cm.</td> </tr> <tr> <th>Online Versions</th> <td>http://nla.gov.au/nla.pic-an23417397</td> </tr> </table> </div>Let’s start to use RDFa to start to build speciﬁc relationships on the page. Let’s start with our subject.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/ xhtml-rdfa-1.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:foaf="http://xmlns.com/foaf/0.1/"> <div about="http://nla.gov.au/nla.pic-an23417397"> <h1 property="dc:title">[Sydney Harbour scene with naval vessels in foreground, and Harbour Bridge in distance] [picture] /</h1> <table> <tr> <th>Date</th> <td property="dc:date">[between 1910 and 1962]</td> </tr> <tr> <th>Format</th> <td property="dc:format">1 negative : acetate, b&w ; 8.7 x 12.1 cm.</td> </tr> <tr> <th>Online Versions</th> <td property="dc:identifier">http://nla.gov.au/nla.pic-an23417397</td> </tr> </table> </div>Predicates as attributes

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/ xhtml-rdfa-1.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:foaf="http://xmlns.com/foaf/0.1/"> <div about="http://nla.gov.au/nla.pic-an23417397"> <h1 property="dc:title">[Sydney Harbour scene with naval vessels in foreground, and Harbour Bridge in distance] [picture] /</h1> <table> <tr> <th>Date</th> <td property="dc:date">[between 1910 and 1962]</td> </tr> <tr> <th>Format</th> <td property="dc:format">1 negative : acetate, b&w ; 8.7 x 12.1 cm.</td> </tr> <tr> <th>Online Versions</th> <td property="dc:identifier">http://nla.gov.au/nla.pic-an23417397</td> </tr> </table> </div>And the objects are the values marked up within the tags.

This is a little geo-explorer application I built. The underlying code has been built incorporating RDFa. As you can see visually, itlooks just like any normal webpage, there is nothing special about it.

By using a Firefox plugin (Fuzz) I can see the underlying semantic structure that exists beyond the visual - what a machinewould see.

RDF Exterior of.... -37.816068 144.961201 Title Latitude Museum Longitude Coverage http://nla.gov.au/nla.pic-an25043941 Creator Sievers, Wolfgang TypeOf Person isPrimaryTopicOf http://nla.gov.au/nla.party-558817It’s a bit easier to see the semantic relationships as a graph. You’ll often see this sort of representation of semantics. You’llnotice that there’s now semantic linkages between 2 different URL’s - neat.

OWL Web Ontology language Used to describe the meanings of terms in vocabularies and the relationships between the terms. Used for applications rather than human presentation.OWL - complex rules deﬁning the properties.

SPARQLSparql. SQL for RDF.

What are the capital cities in countries within Africa? PREFIX abc: <http://example.com/exampleOntology#> SELECT ?capital ?country WHERE { ?x abc:cityname ?capital ; abc:isCapitalOf ?y . ?y abc:countryname ?country ; abc:isInContinent abc:Africa . } http://en.wikipedia.org/wiki/SPARQLAn example query that returns all the capital cities in countries within Africa. You might want to query all the books that werepublished by a company where the authors were born in Melbourne.

Markup HTML using RDFa Provide RDF output in API’sWhat can libraries start to do? This leads to data reuse, mashups, applications. Increased Google rank.

Use external resources such as dbpedia.org - Community effort to extract data from wikipedia & make it available. This isentering the world of linked data.

See the different spellings of Canberra - we don’t need to know all of these, but can extract them from other resources - linkeddata.

For further info, there’s a couple of really good presentations from Sir Tim Berners-Lee on TED

Thanks!Thank you.

Thanks! phagon@nla.gov.au @paulhagonThank you.

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Introduction to the semantic web

by Paul Hagon on Aug 10, 2011

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Introduction to the semantic web Presentation Transcript