Talk at ESWC 2013 summer school in Kalamaki, Crete

1. Institute for Web Science & Technologies – WeST
Programming
the
Semantic Web
Steffen Staab,
Thomas Gottron, Stefan Schegelmann
& Team

2. Steffen Staab 2Programming the Semantic Web
Linked Open Data – Vision of a Web of Data
 „Classic― Web
 Linked documents
 Web of Data
 Linked data entities

3. Steffen Staab 3Programming the Semantic Web
 „Classic― Web
Linked Open Data – Vision of a Web of Data
 Web of Data
ID
ID

4. Steffen Staab 4Programming the Semantic Web
LOD – Base technologies
 IDs: Dereferencable HTTP URIs
 Data Format: RDF
 No schema often / rich schema sometimes
 Links to other data sources
foaf:Document
„Extracting schema ...―
fb:Computer_Scientist
dc:creator
http://dblp.l3s.de/.../NesterovAM98
http://dblp.l3s.de/.../Serge_Abiteboul
rdf:type
„Serge Abiteboul―
dc:title
rdf:type
foaf:name
http://www.bibsonomy.org/.../Serge+Abiteboul
rdfs:seeAlso
1 Statement = 1 Tripel
Subject Predicate Object
rdf:type = http://www.w3.org/1999/02/22-rdf-syntax-ns#type
foaf:Document = http://xmlns.com/foaf/0.1/Document
swrc:InProceedingsrdf:type

5. Steffen Staab 5Programming the Semantic Web
LOD Cloud
… the Web of Linked Data consisting of
more than 30 Billion RDF triples from
hundreds of data sources …
Gerhard Weikum
SIGMOD Blog, 6.3.2013
http://wp.sigmod.org/
Where’s the Data in
the Big Data Wave?

6. Steffen Staab 6Programming the Semantic Web
Some „Bubbles― of the LOD Cloud

7. Steffen Staab 7Programming the Semantic Web
Agenda
 SchemEX
 Where do I find relevant data?
 Efficient construction of a
schema-level index
 Application
 LODatio: Search the LOD cloud
 Active user support
 LiteQ – Language integrated
types, extensions and queries for RDF
graphs
 Exploring
 Programming, Typing

8. Steffen Staab 8Programming the Semantic Web
Motivation
Design Time
Navigation
Run Time
Access

9. Steffen Staab 9Programming the Semantic Web
Example RDF Graph

10. Steffen Staab 10Programming the Semantic Web
Programmers Tasks
1. Explore and understand
the schema of the data
source
• Find a type that represents
dogs
2. Align schema types with
programming language
type system
• From dog RDF data type to
dog data type in the host
programming language
3. Query for instances and
instantiate program data
types
• Get all dogs that have an
owner

11. Steffen Staab 11Programming the Semantic Web
Programmers Tasks vs Our Solution: LITEQ
1. Explore and understand
the schema of the data
source
• Find a type that represents
dogs
2. Align schema types with
programming language
type system
• From dog RDF data type to
dog data type in the host
programming language
3. Query for instances and
instantiate program data
types
• Get all dogs that have an
owner
1. Using NPQL
(NodePathQueryLanguage)
for exploration and definition
2. Type mapping rules for
primitive data types
3. Intensional vs Extensional
 Intensional node path
evaluation provides program
data types
 Extensional node path
evaluation provides instance
data representations

12. Steffen Staab 12Programming the Semantic Web
 Navigating to ex:Dog:
• Start with rdf:Resource as
universal supertype
• Use the subtype navigation
operator „>―
rdf:Resourcerdf:Resource >rdf:Resource > ex:Creaturerdf:Resource > ex:Creature >rdf:Resource > ex:Creature > ex:Dog
Use NPQL schema query language for navigation

13. Steffen Staab 13Programming the Semantic Web
 Retrieving the ex:dog data
type
• Start with the node path
from previous example
• Use the intension method
to get data type description
Using NPQL to retrieve type descriptions
... > ex:Creature > ex:Dog... > ex:Creature > ex:Dog -> Intension
type exDog =
member this.exhasOwner :exPerson =
member this.exhasName :String =
member this.exhasAge :String =
.
.
member this.exTaxNo :Integer =

14. Steffen Staab 14Programming the Semantic Web
Using NPQL to retrieve sets of typed objects
Retrieving objects for all ex:dog
entities
• Start with the node path
from previous example
• Use the extension method
to get the set of typed objects
... > ex:Creature > ex:Dog... > ex:Creature > ex:Dog -> Extension
Provides you with the set of objects containing typed
objects for all instances of ex:Dog
{exHasso}

15. Steffen Staab 15Programming the Semantic Web
 Retrieve all dogs with owners
• Use the known path to
navigate to the dog type
• Use the property selection
operator ―<-― to restrict the
dog data type
• Restrict dog data type to dogs with
ex:hasOwner property
• Use the extension method to
retrieve all dog instances with an owner
ex:Hasso object
Using NPQL to define Instances
... > ex:Dog... > ex:Dog <-... > ex:Dog <- ex:hasOwner... > ex:Dog <- ex:hasOwner -> Extension

16. Steffen Staab 16Programming the Semantic Web
Using LITEQ in Visual Studio
• Line 5: define a datacontext object
• Line 6: Use the datacontext object to define pet data type
•Navigate to pet
•Choose ex:hasOwner property

17. Steffen Staab 17Programming the Semantic Web
Using LITEQ to define types
type dog =rdfResource > exCreature > exDog → Intension
Intensional semantics:
type exDog=
inherit exCreature
hasOwner : exPerson
Using LITEQ to
define types
• The intensional semantic of LITEQ node paths supports
data type definition in the host programming language

18. Steffen Staab 18Programming the Semantic Web
Using LITEQ to retrieve objects
let dogs =rdfResource > exCreature > exDog → Extension
Extensional semantics:
{ex:Hasso,…}
• The extensional semantic of LITEQ node paths supports
query and retrieval of sets of typed objects

19. Steffen Staab 19Programming the Semantic Web
Using LITEQ to define type conditions
let payTax(dogWithOwner : exDog←hasOwner) = …
Type conditions for function
(method) arguments
• LITEQ data types in the host programming language can be
used to define type condidtions, e.g. in method heads
• LITEQ data types are generated in a pre-compile step,
they behave like manually implemented types
• compile-time and run-time type-checking is supported

20. Steffen Staab 20Programming the Semantic Web
Using Type Condidtions
let dogs = rdfResource > exCreature > exDog → Extension
let payTax(dogWithOwner : exDog←hasOwner) = …
for dog in dogs do
match dog with
| :? exDog ← hasOwner as dogWithOwner -> payTax dog
| _ -> ()
Scenario:
• Get all dogs
• Iterate over the set of dogs
• Call paytax method for all dogs with owners

21. Steffen Staab 21Programming the Semantic Web
Agenda
 SchemEX
 Where do I find relevant data?
 Efficient construction of a
schema-level index
 Application
 LODatio: Search the LOD cloud
 Active user support
 LiteQ – Language integrated
types, extensions and queries for RDF
graphs
 Exploring
 Programming, Typing

22. Steffen Staab 22Programming the Semantic Web
Searching the LOD cloud???
?
foaf:Document
fb:Computer_Scientist
dc:creator
x
swrc:InProceedings
SELECT ?x
WHERE {
?x rdf:type foaf:Document .
?x rdf:type swrc:InProceedings .
?x dc:creator ?y .
?y rdf:type fb:Computer_Scientist
}

23. Steffen Staab 23Programming the Semantic Web
Searching the LOD cloud???
SELECT ?x
WHERE {
?x rdf:type foaf:Document .
?x rdf:type swrc:InProceedings .
?x dc:creator ?y .
?y rdf:type fb:Computer_Scientist
}
Index
• ACM
• DBLP

24. Steffen Staab 24Programming the Semantic Web
Schema-level index
 Schema information on LOD
Explicit
Assigning class types
Implicit
Modelling attributes
Class
Entity
rdf:type Entity
Property
Entity 2

25. Steffen Staab 25Programming the Semantic Web
DS1
Schema-level index
E1
P1
E2
XYZP2
C1
C2
C3
P1
P2
C1
C2
C3
DS1

26. Steffen Staab 26Programming the Semantic Web
Typecluster
 Entities with the same Set of types
C1 C2
DS1 DS2 DSm
Cn...
...
TCj

27. Steffen Staab 27Programming the Semantic Web
Typecluster: Example
foaf:Document swrc:InProceedings
DBLP ACM
tc2309

28. Steffen Staab 28Programming the Semantic Web
Bi-Simulation
 Entities are equivalent, if they refer with the same
attributes to equivalent entities
 Restriction: 1-Bi-Simulation
P1 P2
DS1 DS2 DSm
Pn...
...
BSi

29. Steffen Staab 29Programming the Semantic Web
Bi-Simulation: Example
dc:creator
BBC DBLP
bs2608

30. Steffen Staab 30Programming the Semantic Web
SchemEX: Combination TC and Bi-Simulation
 Partition of TC based on 1-Bi-Simulation with
restrictions on the destination TC
C1 C2 Cn...
DS1 DS2 DSm
...
C45 C2 Cn‗...
P1 Pn...
EQC EQC
DS
TCj TCk
EQCj
BSi
SchemaPayload
P2

31. Steffen Staab 31Programming the Semantic Web
SchemEX: Example
DBLP
...
tc2309 tc2101
eqc707
bs2608
foaf:Document swrc:InProceedings fb:Computer_Scientist
dc:creator
SELECT ?x
WHERE {
?x rdf:type foaf:Document .
?x rdf:type swrc:InProceedi
?x dc:creator ?y .
?y rdf:type fb:Computer_Sci
}

32. Steffen Staab 32Programming the Semantic Web
SchemEX: Computation
 Precise computation: Brute-Force
C1 C2 Cn...
DS1 DS2 DSm
...
C12 C2 Cn‗...
P1 Pn...
EQC EQC
DS
TCj TCk
EQCj
BSi
SchemaPayload
P2

33. Steffen Staab 33Programming the Semantic Web
Stream-based Computation of SchemEX
 LOD Crawler: Stream of n-Quads (triple + data source)
… Q16, Q15, Q14, Q13, Q12, Q11, Q10, Q9, Q8, Q7, Q6, Q5, Q4, Q3, Q2, Q1
FiFo
4
3
2
1
1
6
2
3
4
5
C3
C2
C2
C1

34. Steffen Staab 34Programming the Semantic Web
Quality of Approximated Index
 Stream-based computation vs. brute force
 Data set of 11 Mio. tripel

35. Steffen Staab 35Programming the Semantic Web
SchemEX @ BTC 2011
 SchemEX
 Allows complex queries (Star, Chain)
 Scalable computation
 High quality
 Index over BTC 2011 data
 2.17 billion tripel
 Index: 55 million tripel
 Commodity hardware
 VM: 1 Core, 4 GB RAM
 Throughput: 39.500 tripel / second
 Computation of full index: 15h

36. Steffen Staab 36Programming the Semantic Web
Agenda
 SchemEX
 Where do I find relevant data?
 Efficient construction of a
schema-level index
 Application
 LODatio: Search the LOD cloud
 Active user support
 LiteQ – Language integrated
types, extensions and queries for RDF
graphs
 Exploring
 Programming, Typing

37. Steffen Staab 37Programming the Semantic Web
SPARQL queries on LOD ???
SELECT ?x
WHERE {
?x rdf:type foaf:Document .
?x rdf:type swrc:InProceedings .
?x dc:creator ?y .
?y rdf:type fb:Computer_Scientist
}
Index
• ACM
• DBLP
0
hits
1.000
hits
Help!

38. Steffen Staab 38Programming the Semantic Web
Inspiration from web search engines ...
Result set size
Result Snippets
Ranked
Retrieval
Reference to
data source

39. Steffen Staab 39Programming the Semantic Web
Inspiration from web search engines ...
Related Queries

40. Steffen Staab 40Programming the Semantic Web
Did you
mean?
Result set size
Result Snippets
Related
Queries
Ranked
Retrieval
Reference to
data source

41. Steffen Staab 41Programming the Semantic Web
LODatio: Extending the Payload
C1 C2 Cn...
DS-URI1
C12 C2 Cn‗...
P1 Pn...
EQC EQC
TCj TCk
EQCj
BSi
SchemaPayload
P2
DS1
EX1-1
EX1-2
EX1-3
200
ABC
DEF
GHI DS-URI2
DS2
EX2-1
150
XYZ

42. Steffen Staab 42Programming the Semantic Web
C3
P1
Realizing „Related Queries―
C1 C2
TC1
EQC2
DS3
300
SELECT ?x
WHERE {
?x rdf:type C1 .
?x rdf:type C2
}
C1 C2
EQC3
DS4
150
P1
EQC1
DS1
200
DS2
150
C3
BS1
TC2
SELECT ?x
WHERE {
?x rdf:type C1 .
?x rdf:type C2 .
?x P1 ?y
}
SELECT ?x
WHERE {
?x rdf:type C1 .
?x rdf:type C2 .
?x P1 ?y .
?y rdf:type C3 .
}

43. Steffen Staab 43Programming the Semantic Web
Conclusions
 Programming the Semantic Web requires new concepts
 Linked Open Data
 High volume, Varied data, Varying schemata
 Schema-level indices
 Efficient approximative computation
 High accuracy
 Applications
 Search
 Analysis
 ... (many more)

44. Institute for Web Science & Technologies – WeST
Thank you!

45. Steffen Staab 45Programming the Semantic Web
References
1. M. Konrath, T. Gottron, and A. Scherp, ―Schemex – web-scale indexed schema extraction of linked open
data,‖ in Semantic Web Challenge, Submission to the Billion Triple Track, 2011.
2. M. Konrath, T. Gottron, S. Staab, and A. Scherp, ―Schemex—efficient construction of a data catalogue by
stream-based indexing of linked data,‖ Journal of Web Semantics, 2012.
3. T. Gottron, M. Knauf, S. Scheglmann, and A. Scherp, ―Explicit and implicit schema information on the
linked open data cloud: Joined forces or antagonists?,‖ Tech. Rep. 06/2012, Institut WeST, Universität
Koblenz-Landau, 2012.
4. T. Gottron and R. Pickhardt, ―A detailed analysis of the quality of stream-based schema construction on
linked open data,‖ in CSWS‘12: Proceedings of the Chinese Semantic Web Symposium, 2012.
5. T. Gottron, A. Scherp, B. Krayer, and A. Peters, ―Get the google feeling: Supporting users in finding
relevant sources of linked open data at web-scale,‖ in Semantic Web Challenge, Submission to the
Billion Triple Track, 2012.
6. T. Gottron, A. Scherp, B. Krayer, and A. Peters, ―LODatio: Using a Schema-Based Index to Support
Users in Finding Relevant Sources of Linked Data,‖ in K-CAP‘13: Proceedings of the Conference on
Knowledge Capture, 2013.
7. T. Gottron, M. Knauf, S. Scheglmann, and A. Scherp, ―A Systematic Investigation of Explicit and Implicit
Schema Information on the Linked Open Data Cloud,‖ in ESWC‘13: Proceedings of the 10th Extended
Semantic Web Conference, 2013.
8. J. Schaible, T. Gottron, S. Scheglmann, and A. Scherp, ―LOVER: Support for Modeling Data Using
Linked Open Vocabularies,‖ in LWDM‘13: 3rd International Workshop on Linked Web Data
Management, 2013.