Introduction to Linked Data

class: center, middle

# Introduction to Linked Data

## Alexandre Bertails [@bertails](http://twitter.com/bertails)

<br>

permalink: http://bertails.org/2015/04/01/reonomy-linked-data

---

## once upon a time, the Web

* URL

* HTTP

* HTML

---

## let's start with an example

taken from https://dvcs.w3.org/hg/ldpwg/raw-file/ldpatch/ldpatch.html#intro-example

```
@prefix schema: <http://schema.org/> .
@prefix profile: <http://ogp.me/ns/profile#> .
@prefix ex: <http://example.org/vocab#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

<http://example.com/timbl#> a schema:Person ;
  schema:alternateName "TimBL" ;
  profile:first_name "Tim" ;
  profile:last_name "Berners-Lee" ;
  schema:workLocation [ schema:name "W3C/MIT" ] ;
  schema:performerIn _:b1, _:b2 ;
  ex:preferredLanguages ( "en" "fr" ).

_:b1 schema:name "F2F5 - Linked Data Platform" ;
  schema:url <https://www.w3.org/2012/ldp/wiki/F2F5> .

_:b2 a schema:Event ;
  schema:name "TED 2009" ;
  schema:startDate "2009-02-04" ;
  schema:url <http://conferences.ted.com/TED2009/> .
```

---

## one model, several syntaxes

awesome online RDF converter: [http://rdfvalidator.mybluemix.net/](http://rdfvalidator.mybluemix.net/)

#### default JSON-LD output

```
{
  "@graph" : [ {
    "@id" : "_:b1",
    "@type" : "schema:Event",
    "name" : "TED 2009",
    "startDate" : "2009-02-04",
    "url" : "http://conferences.ted.com/TED2009/"
  }, {
    "@id" : "_:b2",
    "name" : "F2F5 - Linked Data Platform",
    "url" : "https://www.w3.org/2012/ldp/wiki/F2F5"
  }, {
    "@id" : "_:b3",
    "name" : "W3C/MIT"
  }, {
    "@id" : "http://example.com/timbl#",
    "@type" : "schema:Person",
    "ex:preferredLanguages" : {
      "@list" : [ "en", "fr" ]
    },
    "first_name" : "Tim",
    "last_name" : "Berners-Lee",
    "alternateName" : "TimBL",
    "performerIn" : [ "_:b1", "_:b2" ],
    "workLocation" : "_:b3"
  } ],
  ...
}
```

Not pretty, but that's the same data!  (see [graph isomorphism](http://www.w3.org/TR/rdf11-concepts/#h3_graph-isomorphism))

---

## graph visualization

from RDF/XML and the [W3C RDF(/XML <cough>) Validator](http://www.w3.org/RDF/Validator/)

[.sized[![RDF graph](rdf-graph.png)]](rdf-graph.png)

---

## JSON-LD [1/2]

In the [JSON-LD Playground](http://json-ld.org/playground/), we can play with the **context** and the **frame** to change the shape of the data:

```
{
  "@id": "http://example.com/timbl#",
  "@type": "schema:Person",
  "preferredLanguages": [ "en", "fr" ],
  "first_name": "Tim",
  "last_name": "Berners-Lee",
  "alternateName": "TimBL",
  "performerIn": [
    {
      "@id": "_:b0",
      "@type": "schema:Event",
      "name": "TED 2009",
      "startDate": "2009-02-04",
      "url": "http://conferences.ted.com/TED2009/"
    },
  ...
}
```

Once again, this is the very same data.

---

## JSON-LD [2/2]

* without a context **and** a frame, JSON-LD won't be used by Web Developers

* JSON-LD encourages you to work on a tree, while RDF is a graph

* don't sacrifice correctness for "pragmatism": JSON itself is usually not enough for data

---

## the RDF 1.1 data model

as defined in [RDF 1.1 Concepts](http://www.w3.org/TR/rdf11-concepts/#section-rdf-graph)

```
graph       ::= Set(triple)
triple      ::= (node, iri, node)
node        ::= iri | bnode | literal
iri         ::= URI with Unicode
bnode       ::= local node identifier
literal     ::= (lexicalForm, datatype, Option(lang))
lexicalForm ::= string
datatype    ::= iri
lang        ::= string
```

---

## some examples

* `<http://example.com/foo>` is a IRI
* `xsd:integer` is a prefixed IRI for <http://www.w3.org/2001/XMLSchema#integer>
* `_:b2719` is a Blank Node
* `"foo"` is a string literal (`"foo"`, `xsd:string`, no lang)
* `42` is an integer (`"42"`, `xsd:integer`, no lang)
* `"foo"@en` is an i18ned string ("foo", `rdf:langString`, `"en"`)

---

## datasets

```
dataset     ::= (graph, Set(namedGraph))
namedGraph  ::= (graphName, graph)
graphName   ::= iri | bnode
```

in plain English: a **dataset** is made of one **default graph** and a collection of **named graphs**, graphs with a name (either IRI or Blank Node).

### differents contexts

*database* vs the *web*

---

## Semantic Web^W^WLinked Data timeline

source: [Marin Dimitrov, CTO @ Ontotext](https://www.quora.com/What-are-the-main-reasons-for-the-slow-uptake-of-Semantic-Web-technologies/answer/Marin-Dimitrov)

[.sized80[![Semantic Web timeline](semantic-web-timeline.png)]](semantic-web-timeline.png)

---

## to go further

### technologies

* [schema.org](http://schema.org)
* [JSON-LD in Gmail](https://developers.google.com/schemas/formats/json-ld)
* [Facebook's Open Graph protocol](http://ogp.me/)
* [Linked Data Platform 1.0](http://www.w3.org/TR/ldp/)

### datasets

* http://linkeddata.org/
* http://dbpedia.org/