web of data - aleksandar stanimirovic
TRANSCRIPT
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SEMANTIKA PODATAKA- OSNOVI I TEHNOLOGIJE
- Aleksandar Stanimirović
14.03.2017.
Web of Data(Semantic Web)
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Web of Data
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Web of Data
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Web of Data
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Web of Data
• Syntax is how to say something.
• Semantic is the meaning behind what you say.
• Sintaksa predstavlja gramatiku jednog jezika ili forme izražavanja.
• Semantika definiše značenje.• Različite sintakse mogu da imaju istu semantiku.
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Semantic Web• Sir Tim Berners-Lee et al., Scientific American, 2001:
– “An extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation.”
• Vizija budućeg Web-a (web značenja – semantike)– Nije ZAMENA već PROŠIRENJE postojećeg Web-a– Omogućava bolju kooperaciju između ljudi i mašina (softverskih
agenata)– Veća autonomija mašina u obradi podataka
• Veliki broj standarda, markup jezika, alata• U osnovi su meta podaci i ontologije.
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Semantic Web
Semantic Web stack
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Meta podaci
• Meta podaci – podaci o podacima• Meta podaci opisuju značenje podataka• Zašto meta podaci:
– Da obezbede struktuirani opis (značenje, sadržaj, struktura i svrha) određenog resursa
– Da omoguće deljenje podataka/informacija– Da omoguće lakše pronalaženje i pretragu resursa– Da minimizuju ponavljanje i gubljenje podataka– Da podrže inteligentne softverske agente
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Meta podaci
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Meta podaci
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RDF• Resource Description Framework• Osnovna namena: opis i razmena meta podataka• Jednostavan model podataka
– Reprezentacija meta podataka– Formalni opis semantike podataka koji mašine mogu da OBRAĐUJU i RAZUMEJU
• Različite standardi za predstavljanje (RDF flavours)– RDF/XML– N3 (Notation 3)/Turtle– TriG– N-Triples– RDFa– TriX– ....
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RDF• RDF graph is a collection of RDF triplets
Subjekat ObjekatPredikat
Alfama LisbonlocatedIn
LisbonhasPopulation
3035000
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RDF
Lisbon
“Lisbon”
“Lisboa”
hasName
hasName
Subjekat Predikat Objekat
http://dbpedia.org/page/Lisbon hasName “Lisbon”
http://dbpedia.org/page/Lisbon hasName “Lisboa”
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RDF
Lisbon
“Lisbon”
“Lisboa”
hasName
hasName
3035000hasPopulation
Alfama“Alfama”
hasName
locatedIn
Subjekat Predikat Objekat
http://dbpedia.org/page/Lisbon hasName “Lisbon”
http://dbpedia.org/page/Lisbon hasName “Lisboa”
http://dbpedia.org/page/Lisbon hasPopulation 3035000
http://dbpedia.org/page/Alfama hasName “Alfama”
http://dbpedia.org/page/Alfama locatedIn http://dbpedia.org/page/Lisbon
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Ontologije
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Ontologije• Meta podaci obezbeđuju struktuirani opis resursa
– Npr. za slučaj dokumenta meta podaci mogu da sadrže: title, description, keywords, author, educational level, version, location, language, date created, ...
• Dalja struktura meta podataka je obezbeđena šemom meta podataka ili ontologijom– Npr. Za slučaj ontologije koja opisuje fudbalski klub precizirano je da
svaki fudbalski klub ima golmana i trenera. Zbog toga za meta podatke o svakom klubu očekujemo informacije o golmanu i treneru.
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Ontologije
• Ontologija obezbeđuje deljivo i zajedničko razumevanje određenog domena.
• Ontologija definiše termine (rečnik, vokabular) koji se koriste za opisivanje i predstavljanje određenog domena ljudskog znanja.
• Povezuju ljudsko razumevanje simbola sa mogućnošću njihove obrade od strane mašina.
• Primeri: rečnik, thesaurus, taksonomije, top-level ontologije
“An ontology is an explicit specification of a conceptualization.” - T. R. Gruber
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Ontologije
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Ontologije• Specifikacija ontologije sadrži:
– Opise KONCEPATA (classes, concepts) određenog domena– Opise SVOJSTAVA (properties, attributes) koje ti koncepti imaju– Opise mogućih RELACIJA (relations) koje koncepti i njihova svojstva
mogu da imaju sa drugim konceptima ili svojstvima (u istom ili različitim domenima)
– PRAVILA kako/kada se relacije mogu primeniti– INSTANCE (individuals) koncepata ontologije
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Ontologije
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Ontologije• Tipovi ontologija:
– Aplikativne ontologije – razvijene za potrebe jedne aplikacije• Ponekad steknu veliku popularnost i postanu de-facto standard
– Domenske ontologije – modeliraju specifičan domen ili deo sveta od interesa (pravo, medicina, genetika, geografija, računarstvo i sl.)
– Top-level (Upper-level, foundation) ontologije – opisuju generalne koncepte koji su zajednički u svim domenima
• Primeri: Dublin Core, FOAF (društvene mreže), GeoNames, WordNet
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OntologijeLinkedData
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OntologijeLinkedData
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Ontologije
• Anotacije• RDFa (Schema.org), Open Graph protocol,
Microdata, JSON-LD <div itemscope itemtype ="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <span>Director: <span itemprop="director">James Cameron</span> (born August 16, 1954)</span> <span itemprop="genre">Science fiction</span> <a href="../movies/avatar-theatrical-trailer.html" itemprop="trailer">Trailer</a> </div>
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Ontologije
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SPARQL
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SPARQL• SPARQL Protocol and RDF Query Language
SELECT ?f ?l ?aWHERE { ?f rdf:type dbo:Film . ?f rdfs:label ?l . ?f dbo:abstract ?a FILTER (regex (?l, "Batman Begins", "i") && (lang(?l) = lang(?a)))}ORDER BY lang(?l)
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SWRL
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SWRL• Semantic Web Rule Language• SWRL se koristi za predstavljanje pravila i logike• Pravila imaju formu implikacije između premisa i zaključka.• Ukoliko su sve premise tačne onda je tačan i zaključak.• Zaključak postaje deo ontologije.
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SWRL
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Mašine za zaključivanje
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Mašina za zaključivanje