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 2 ¿Qué es la Web Semántica? ! Conjunto de tecnologías estándar para conseguir una Web de Datos " " " 1. “AAA slogan”: Anyone can say Anything about Any Topic Distribuida Interpretable por máquinas (machine-readable) # ! Características de la Web Semántica " 2. Mundo abierto Deja de ser orientada a presentación... Con referencias globales: URIs " " " ¿Quién asigna los nombres? 4. Network effect Formatos comunes de datos # ¿Podemos asumir que tenemos toda la información? 3. Sistema de nombrado no único Web Semántica proporciona infraestructura para una Web más “lista” " Sin control central, desacuerdos... " Énfasis en integración de datos Crecimiento exponencial... Modelos # Relacionar datos con conceptos del mundo real 3 4 “The Semantic Web Layer Cake” Modelos en la Web Semántica ! Hacen falta modelos para organizar la información " ! Diferentes grados de informalidad/formalidad de los modelos " " ! Continuamente utilizados por los humanos Informales: dependientes de contexto, diferentes interpretaciones Formales: términos precisos (definidos), reglas Modelos en la Web Semántica " " " Máquinas necesitan modelos formales Combinación de diferentes modelos (fuentes) Diferentes niveles de expresividad 5 6 Índice Motivación de RDF ! Resource Description Framework (RDF) " " Lenguaje para representar información de recursos Requisitos # 1. Introducción Web Semántica # # 2. Resource Description Framework (RDF) # " ! 7 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 8 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 34 ! 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 34 CHAPTER 3 RDF—The Basis of the Semantic Web ! 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. 11 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 12 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. ! Namespaces Objetos pueden ser recursos o literales Reification Nodos vacíos Información ordenada Serialización de RDF " that is common across the Web. If two agents on " ! ! http://challenge.semanticweb.org/ Magazines " " 15 http://www.w3.org/2001/sw/ Semantic Web Challenge " Diferentes sintaxis: N-triples, N3, RDF/XML, etc. http://www.w3.org/ W3C Semantic Web Activity " ! 2008 A. Gómez-Pérez, M. Fernández-López, O. Corcho: Ontological engineering, 2004 Especificaciones de RDF, RDFS, OWL (W3C) " ! 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 " ! 14 Más información ! ! 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”?.. 13 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 ! ChannelIslands partOf e KingLear HenryV partOf tOf par TheTempest WintersTale Othello HenryV te wro wrote e w wrotewrot " NorthernIreland LovesLaboursLost URIs como identificadores globales " wrote " wrote " wrote ot e Ventajas de las triplas " ! 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 38 IEEE Intelligent Systems (Communications of the ACM, IEEE Internet Computing...) 16 39