INTRODUCCIÓN A LA WEB SEMÁNTICA Y A RDF Índice ¿Qué es

Índice
TECNOLOGÍAS EMERGENTES EN SISTEMAS TELEMÁTICOS
BLOQUE IST de MUITIC-UVa
INTRODUCCIÓN A LA WEB SEMÁNTICA Y A RDF
1. Introducción Web Semántica
2. Resource Description Framework (RDF)
Guillermo Vega Gorgojo
Juan Ignacio Asensio Pérez
NOVIEMBRE 2009
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¿Qué es la Web Semántica?
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Conjunto de tecnologías estándar para conseguir una
Web de Datos
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1. “AAA slogan”: Anyone can say Anything about Any Topic
Distribuida
Interpretable por máquinas (machine-readable)
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Características de la Web Semántica
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2. Mundo abierto
Deja de ser orientada a presentación...
Con referencias globales: URIs
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¿Quién asigna los nombres?
4. Network effect
Formatos comunes de datos
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¿Podemos asumir que tenemos toda la información?
3. Sistema de nombrado no único
Web Semántica proporciona infraestructura para una
Web más “lista”
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Sin control central, desacuerdos...
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Énfasis en integración de datos
Crecimiento exponencial...
Modelos
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Relacionar datos con conceptos del mundo real
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“The Semantic Web Layer Cake”
Modelos en la Web Semántica
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Hacen falta modelos para organizar la información
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Diferentes grados de informalidad/formalidad de los
modelos
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Continuamente utilizados por los humanos
Informales: dependientes de contexto, diferentes
interpretaciones
Formales: términos precisos (definidos), reglas
Modelos en la Web Semántica
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Máquinas necesitan modelos formales
Combinación de diferentes modelos (fuentes)
Diferentes niveles de expresividad
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Índice
Motivación de RDF
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Resource Description Framework (RDF)
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Lenguaje para representar información de recursos
Requisitos
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1. Introducción Web Semántica
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2. Resource Description Framework (RDF)
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Distribución de datos en la Web
Compartición de terminologías/esquemas
Identificadores globales
Flexible (“AAA slogan”)
La base de la Web Semántica...
Vamos a verlo en un ejemplo
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machine is responsible for information about “Sonnet 78” and Edward II,
whereas another is responsible for information about As You Like It.
This distribution solution provides considerable flexibility, since the
machines can share the load of representing information about several indiviEjemplo de distribución de datos en la Web
duals. But because it is a distributed representation of data, it requires some
coordination between the servers. In particular, each server must share information about
the columns.
Does the second column on one server correspond to
! Datos
de partida
Table 3-1
Ejemplo de distribución de datos en la Web
Distributing Data Across the Web
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! Fila por fila...
Basis of the Semantic Web
CHAPTER 3 RDF—The
Tabular Data about Elizabethan Literature and Music
ID
Title
Author
Medium
Year
1
As You Like It
Shakespeare
Play
1599
2
Hamlet
Shakespeare
Play
1604
3
Othello
Shakespeare
Play
1603
Year
NeedsMedium
common schema—which
column is which?
1599 Play
4
“Sonnet 78”
Shakespeare
Poem
1609
1604 Play
5
Astrophil and Stella
Sir Phillip Sidney
Poem
1590
1603 Play
6
Edward II
Christopher Marlowe
Play
1592
7
Hero and Leander
Christopher Marlowe
Poem
1593
7
8
Greensleeves
Henry VIII Rex
Song
1525
3
1
As You Like It
1609 Poem
1590 Poem
1592
PlayLeander
Hero and
1593
OthelloPoem
1525 Song
9
Shakespeare Play 1599
Needs to reference
entities—which thing
4 Sonnet
Shakespeare
Poem 1609
are we 78
talking
about?
6 Edward II Christopher Marlowe Play 1592
Author
Title
Shakespeare
As You Like It
Shakespeare
Shakespeare
Christopher Marlowe
Poem 1593
Shakespeare
Shakespeare
1603
Sir Play
Phillip Sidney
FIGURE 3-1
Distributing data across the Web, row by row.
Ejemplo de distribución de datos en la Web
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CHAPTER 3 RDF—The Basis of the Semantic Web
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Columna por columna...
Year Medium
1599 Play
1604 Play
1603 Play
1609 Poem
1590 Poem
1592 Play
1593 Poem
1525 Song
Needs to reference
entities—which thing
are we talking about?
Author
Title
Shakespeare
As You Like It
Shakespeare
Hamlet
Shakespeare
Othello
Shakespeare
“Sonnet 78”
Sir Phillip Sidney
Astrophil and Stella
Christopher
Marlowe
Edward II
Christopher
Marlowe
Greensleeves
Hero and Leander
Henry VIII Rex
FIGURE 3-2
Distributing data across the Web, column by column.
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Hamlet
Othello
“Sonnet 78”
Astrophil and Stella
Christopher
Marlowe
Edward II
Christopher
Marlowe
Greensleeves
10
Hero and Leander
Henry VIII
the same information as the second column
on Rex
another server? This is not an
insurmountable
and, in fact, it isde
a fundamental
of data distriFIGURE
3-2 problem,
Ejemplo
de distribución
datos enproblem
la Web
bution.
Theredata
must
be some
agreed-on
coordination
between the servers. In this
Distributing
across
the Web,
column by
column.
example, the servers must be able to, in a global way, indicate which property
! column
each
to.
Celdacorresponds
por celda...
Figure 3-2 shows another strategy, in which each server is responsible for
one or more complete columns from the original table. In this example, one
server is responsible for the publication dates and medium, and another server
is responsible for titles. This solution is flexible in a different way from the solution of Figure 3-1. The solution in Figure 3-2 allows each machine to be responsible for one kind of information. If we are not interested in the dates of
Needs to reference both
publication, Medium
we needn’t considerschema
information
from that server. If we want to
and entities
Row
7 Poem new about the entities (say, how many pages long the manuspecify
something
script is), we can add a Title
new server with that information without disrupting the
Row 2 Hamlet
others.
Author
This solution is similar to the solution in Figure 3-1 inRow
that4 itShakespeare
requires some
coordination between the servers. In this case, the coordination has to do with
the identities of the entities to be described.
Year How do I know that row 3 on one
server refers to the same entityRow
as 2row
3 on another server? This solution
1604
requires a global identifier for the entities being described.
The strategy outlined in Figure Medium
3-3 is a combination of the previous two straRow 6 Play
tegies, in which information
is neither distributed row by row nor column by
FIGURE
column
but3-3
instead is distributed cell by cell. Each machine is responsible for
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some
numberdata
of across
cells in
table.
This
Distributing
thethe
Web,
cell by
cell.system combines the flexibility of both
33
wrote
wro
te
wr
ot
e
wr
te
wro tee
t
wroo
isIn
ro
te
pa
IsleOfMan
Othello
MeasureForMeasure
livedIn
Hamlet
AsYouLikeIt
AnneHathaway
LovesLaboursLost
TwelfthNight
AsYouLikeIt
wrote
wr
wr ote
ot
e
e
ot
e
wr wrot e
t
wro ote
wr
(a)
UK
partOf
UK
partOf
Of
rt
Of
ar
t
pa
tpOf
par
Wales
MeasureForMeasure
LovesLaboursLost
AsYouLikeIt
IsleOfMan
Scotland
TwelfthNight
Scotland
FIGURE 3-6
(b)
Graphic representation of triples describing Shakespeare’s
plays and parts of the United
Kingdom.3-5
Combined
FIGURE
graph of all triples about Shakespeare and the United Kingdom.
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Namespaces
Objetos pueden ser recursos o literales
Reification
Nodos vacíos
Información ordenada
Serialización de RDF
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that is common across the Web. If two agents on
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http://challenge.semanticweb.org/
Magazines
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http://www.w3.org/2001/sw/
Semantic Web Challenge
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Diferentes sintaxis: N-triples, N3, RDF/XML, etc.
http://www.w3.org/
W3C Semantic Web Activity
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2008
A. Gómez-Pérez, M. Fernández-López, O. Corcho: Ontological
engineering, 2004
Especificaciones de RDF, RDFS, OWL (W3C)
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naming leads to global network effects.
URIs and URLs look exactly the same, and in fact, a URL is just a special
case of the URI. Why does the Web have both of these ideas? Simplifying somewhat, the URI is an identifier with global (i.e., “World Wide” in the “World
Wide Web” sense) scope. Any two Web applications in the world can refer
to the
same thing
by referencing
the same URI.
But the syntax of the URI
D. Allemang, J. Hendler:
Semantic
Web
for the Working
Ontologist,
makes it possible to “dereference” it—that is, to use all the information in
Libros
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Más información
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HenryV
WintersTale
the Web want to refer to the same resource, recommended practice on the
URL—for example, http://www.WorkingOntologist.org/Examples/Chapter3/
is afor
themidento agree to a common URI for that resource. This is not a stipuShakespeare.owl#Shakespeare. But the significance of the Web
URI as
global
lation
that isa particular
to the Semantic Web but to the Web in general; global
tifier for a Web resource is often not appreciated. A URI
provides
global
Más de RDF
!
KingLear
TheTempest
Othello
Graphic
of triples
describing
Shakespeare’s
plays and
parts
of the United
casual representation
users of the Web
today because
of the
special, but typical,
case
of the
Kingdom.
URL—for example, http://www.WorkingOntologist.org/Examples/Chapter3/
Shakespeare.owl#Shakespeare. But the significance of the URI as a global idenforthe
a resource
tifier for
a Web
resource
often not
appreciated.
URI provides
atypical,
global case of
casual
users
of the
Webistoday
because
of theA special,
butidentification
!
Macbeth
Hamlet
IsleOfMan
(b)
wrot
e
e
ot
Wales
Of
wr
ChannelIslands
ChannelIslands
Para detectar si un nodo de un grafo es el mismo que el de
otro grafo
¿Y si usamos “tags”?..
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t
par
f
tO
par
partOf
partOf
NorthernIrelandpartOf
NorthernIreland
p
partOf
art
Of
England
setIn
Shakespeare
married
(a)
TwelfthNight
England
Scotland
MeasureForMeasure
wrote
wrote
Sencillez
Fácilmente distribuibles
Fácilmente recombinables
Wales
Stratford
Hamlet
WintersTale
FIGURE 3-5
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ChannelIslands
partOf
e
KingLear
HenryV
partOf
tOf
par
TheTempest
WintersTale
Othello
HenryV
te
wro
wrote
e
w
wrotewrot
"
NorthernIreland
LovesLaboursLost
URIs como identificadores globales
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wrote
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wrote
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wrote
ot
e
Ventajas de las triplas
"
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wr
!
wrote
"
sujeto - predicado - objeto
Conjunto de triplas puede representarse como un grafo
dirigido
Macbeth
UK
partOf
TheTempest
Of
e
ot
wr
wrote
wro
te
wr
ot
e
wr
ot
e
"
KingLear
England
Shakespeare
El elemento básico de RDF es la tripla
Macbeth
rt
CHAPTER 3 RDF—The Basis of the Semantic Web
ot
wr
!
Namespaces, URIS, and Identity
Ejemplo de combinación de triplas en RDF
Shakespeare
38
tOf
Las triplas de RDF
CHAPTER 3 RDF—The Basis of the Semantic Web
par
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IEEE Intelligent Systems
(Communications of the ACM, IEEE Internet Computing...)
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