Resource Description Framework M ore Sem antic for the Web! RDF and XUL in M ozilla/Netscape 6
Johannes Henkel
[email protected] www.jhenkel.de Dec 14 2000, CSCI 7818
XML − a programmer’s paradise? Representing data structures − gap between plain XML and OOP or O R models? Understanding ?
Exchanging data between applications without pain?
Level of machine readability? Introduction of a new data model for every XML based standard?
What would you like to do with all that data out there in the web? Storage / Access
Integration Manipulation
Querying
Inference / Proofing Do all these activities based on standards so that you spent the minimal amount of time with programming / porting etc.
Tim Berners Lee’s roadmap tow ards a "semantic w eb" ublilinn DDub CCoorere EElelemmeennt t SSeet t
Mo z
P3P
KKRR ddaatata
KR rule s
Web of Trust P roo f
Lo gi c
O nto lo gy S uppo rt R DF S ch e ma
R DF S ynta x in XML
XML D i g. S i g.
R DF : ba sic E R −like mo de l
N a m e s pa c e s
XML−S ch e ma
XML − S tructure d do cume nts
Unve rsa l R e so urce Ide ntifie rs
(Unico de )
References: Ti m Berners Lee: "Buil di ng the future" (thi s sli de), http: //www. w3.org/2000/Tal ks/0906−xml web−tbl /sli de9−0.html Ti m Berners Lee: "Reali si ng the Full Potenti al of the Web", http: //www. w3.org/1998/02/Potenti al . html Ti m Berners Lee: "The future of the web", http: //www. w3.org/1999/04/13−tbl .html Homepage of Ti m Berners Lee: http: //www. w3.org/Peopl e/Berners−Lee/
Concepts of RDF: A first Example http://www.cs.colorado.edu/~ kena/classes/7818/f00
Subjec t (R es ourc e)
Crea to r
Predic ate (Property) Sentenc e
Ke n Ande rso n
O bjec t (Literal)
Crea to r(R e so urce ("h ttp: //... "))="Ke n Ande rso n" Ha sCrea to r(R e so urce ("h ttp: //... "), "Ke n Ande rso n") Ha sP ro pe rty(R e so urce ("h ttp: //... /7818 /f00 /"), "Crea to r", "Ke nAnde rso n")
HAS Reference: W3C Rec: "ResourceDescri pti on Framework (RDF) Model and Syntax Speci fi cati on", 22 Feb 1999, http: //www. w3.org/TR/1999/REC−rdf−syntax−19990222
Concepts of RDF: A first Example (cont.)
http://www.cs.colorado.edu/~ kena/classes/7818/f00
Crea to r
Na m e Email
Ke n Ande rso n
ke na @cs. co lo ra do . e du
! E XIS TS x. Ha sP ro pe rty(R e so urce ("h ttp: //... /f7818 /f00 "), "Crea to r", x) AND Ha sP ro pe rty(x, "Na me ", "Ke n Ande rso n") AND Ha sP ro pe rty(x, "E ma il", "ke na @cs. co lo ra do . e du")
Semantic Web: Architectural Goals Scalability RDF: Scale KR up for worldwide use WWW: Scale hypertext up for worldwide use Everyone should be able to express anything No consistency guarantee No centralized approach
Enable prooving without making it a requirement for the usefulness of the web But: You might express queries that are undecidable (no closed world, "A and not A") Reference: Ti m Berners Lee: "What the Semanti c Web can represent", 1998, http: //www. w3.org/Desi gnIssues/RDFnot. html
How much semantic does our example contain thus far? Mapping to formulae in predicate calculus (not defined by standard) Using URLs allows for uniform access to locate resources: Resource("http://...") Doesn’t "access" really mean "semantic"? The names of the properties are just arbitrary strings thus far: "Email" / "Name"
Also, "Ken Anderson" is just a string.
In RDF, properties (the relations itself) are first− class values, specified in RDF Schemas − we could add even more semantic declaratively Higher order statements possible
RDF containers: Bag, Sequence, Alternative Bag: An unordered list of resources or literals.
Sequence: An ordered list of resources or literals. Alternative: A list of resources or literals that represent alternatives for the (single) value of a property.
No Set. the rdf:type property is used to assign types specified in RDF Schema the containers are built−in types
So why do we not just use the XML Schema m e c h a n is m s ?
http://frwebgate.acc es .gpo.gov/ s upremec ourt/00−949_dec 12.fdf
approved_by
rdf:type rdf:Bag
rd f:_ 1
A rdf:Bag example
2 :f _ rd 3 _ : f rd 4 rdf:_ 4 _ : f d r
rdf:_4 rdf:_ 4 rdf : rd _4 f:_ 4
R ehnquis t Sc alia Thomas
O ’Connor Kennedy Stevens Souter
Gins burg Breyer
ap pr ov ed _b y
What about this variation?
... ... ...
http://frwebgate.acc es .gpo.gov/ s upremec ourt/00−949_dec 12.fdf
y b _ d e v appro ... ... ... ...
R ehnquis t Sc alia Thomas
O ’Connor Kennedy Stevens Souter
Gins burg
Valid R DF , but Stevens , Souter Gins burg and Breyer diss ented!
Breyer
A statement about a statement h ttp: //www. sta te . fl. us/
Al Gore
rd f:s ub jec
t
rdf :pr ed ica
ele
e p y t : f rd
: f rd
t c je b o
te
ct:
sa
rdf: S ta te me nt
e le ct: wo nBy
y idB h ttp: //www. cnn. co m/
CNN s aid that Al Gore won F lorida
What about syntax?! Tw o Fl a v o r s : Basic Serialization Syntax Basic Abbreviated Syntax
