From data to knowledge –
profiling and interlinking Web datasets
Stefan Dietze
L3S Research Center
31/07/14 1 Stefan Dietze
Recent work on Linked Data exploration/discovery/search
Entity interlinking & dataset interlinking recommendation
Dataset profiling
Data consistency & conflicts
Research areas
Web science, Information Retrieval, Semantic Web & Linked Data, data & knowledge integration (mapping, classification, interlinking)
Application domains: education/TEL, Web archiving, …
Some projects
Introduction
http://www.l3s.de/
31/07/14 2
See also: http://purl.org/dietze
Stefan Dietze
…why are there so few datasets actually used?
Date reuse and in-links focused on trusted „reference graphs“ such as DBpedia, Freebase etc
Long tail of LD datasets which are neither reused nor linked to (LOD Cloud alone 300+ datasets, 50 bn triples)
Explanations?
Linked Data is awesome, but...
31/07/14
„HTTP-accessibility“ (SPARQL, URI-dereferencing)
„Structure“ & „Semantics“ (=> shared/linked vocabularies)
„Interlinked“
„Persistent“
Hm,
really?
Stefan Dietze
Linked data is more diverse than we think
SPARQL endpoint availability over time [Buil-Aranda et al 2013]
Accessibility of datasets?
Less than 50% of all SPARQL endpoints actually responsive at given point of time
“THE” SPARQL protocol? No, but many variants & subsets
…
“Semantics”, links, quality?
…data consistency? [? Yuan2014 ?]
…data accuracy (eg DBpedia)? [Paulheim2013]
…vocabulary reuse? [D’AquinWebSci13]
…schema compliance (RDFS, schemas) [HoganJWS2012]
Stefan Dietze
SPARQL Web-Querying Infrastructure: Ready for Action?,
Carlos Buil-Aranda, Aidan Hogan, Jürgen Umbrich Pierre-Yves
Vandenbussch, International Semantic Web Conference 2013,
(ISWC2013).
Assessing the Educational Linked Data Landscape, D’Aquin, M., Adamou, A.,
Dietze, S., ACM Web Science 2013 (WebSci2013), Paris, France, May 2013.
Type Inference on Noisy RDF Data, Paulheim H., Bizer, C. Semantic Web – ISWC
2013, Lecture Notes in Computer Science Volume 8218, 2013, pp 510-525
An empirical survey of Linked Data conformance. Hogan, A., Umbrich, J., Harth,
A., Cyganiak, R., Polleres, A., Decker., S., Journal of Web Semantics 14, 2012
Too many/diverse datasets, too little knowledge
Stefan Dietze 31/07/14
? ? ?
? ? ?
Which datasets are useful & trustworthy for case XY (eg „learning about the solar system“) ? Which topics are covered?
Types: which datasets describe statistics, videos, slides, publications etc?
Currentness, dynamics, accessability/reliability, data quantity & quality?
db:Astro. Objects
Dataset Metadata
Stefan Dietze 31/07/14
BIBO
AAISO
FOAF
contains
Entity disambiguation & linking [ESWC13]
Topic profile extraction [WWW13, ESCW14]
db:Astronomy
db:Astro. Objects
Dataset
Catalog/Registry
yov:Video
po:Programme
BBC Programme
<po:Programme …>
<po:Series>Wonders of the Solar System</.>
<po:Actor>Brian Cox</…>
</po:Programme…>
<yo:Video …>
<dc:title>Pluto & the
Dwarf Planets</dc:title>
…
</yo:Video…>
Yovisto Video
bibo:Fil bibo:Fi
bibo:Film
Schema mappings [WebSci13]
Data curation, linking and dataset profiling
Schemas/vocabularies on the Web: XKCD 927
Stefan Dietze 31/07/14
https://xkcd.com/927/ schemas & vocabularies
typeX typeX
Schema assessment and mapping
Co-occurence of data types (in 146 datasets: 144 Vocabularies, 588 highly overlapping types, 719 Properties)
Co-occurence after mapping into most frequent schemas
(201 frequent types mapped into 79
classes)
Assessing the Educational Linked Data Landscape,
D’Aquin, M., Adamou, A., Dietze, S., ACM Web Science
2013 (WebSci2013), Paris, France, May 2013.
bibo:Film
bibo:Document
po:Programme sioc:Item
31/07/14
foaf:Document
yov:Video
typeX
LinkedUp Data Catalog in a nutshell
http://datahub.io/group/linked-education
http://data.linkededucation.org/linkedup/catalog/
RDF (VoID) dataset catalog: browse & query distributed datasets
Live information about endpoint accessibility
Federated queries using type mappings
Stefan Dietze 31/07/14
http://datahub.io/group/linked-education
31/07/14
Dataset interlinking recommendation Candidate datasets for interlinking?
13
t
Linkset1
Linkset2
Approach
Given dataset t, ranking datasets from D according to probability score (di, t) to contain linking candidates (entities)
Features:
Vocabulary overlap
Existing links (SNA)
Linking candidates likely if datasets share common (a) schema elements, or (b) links (friend of a friend)
Conclusions
Roughly 60% MAP for both approaches
Future work: quantity of links, extraction of experimental data from datasets…
Lopes, G.R., Paes Leme, L.A.P., Nunes, B.P., Casanova, M.A.,
Dietze, S., Recommending Tripleset Interlinking through a
Social Network Approach, The 14th International Conference
on Web Information System Engineering (WISE 2013),
Nanjing, China, 2013.
Paes Leme, L. A. P., Lopes, G. R., Nunes, B. P., Casanova,
M.A., Dietze, S., Identifying candidate datasets for data
interlinking, in Proceedings of the 13th International
Conference on Web Engineering, (2013).
Rank
1 DBLP
2 ACM
3 OAI
4 CiteSeer
5 IBM
6 Roma
7 IEEE
8 Ulm
9 Pisa
?
?
Stefan Dietze
<yo:Video 8748720>
<dc:title>Pluto & the
Dwarf Planets</dc:title>
…
</yo:Video 8748720>
Video
Topics/categories addressed? Relatedness of resources/entities? (types, semantics)
<po:Programme519215>
<po:Series>Wonders of the Solar
System</po:Series>
<po:Episode>Emp. of the Sun</po:Episode>
<po:Actor>Brian Cox</po:Actor>
</po:Programme519215 >
Programme
Combining a co-occurrence-based and a semantic measure
for entity linking, B. P. Nunes, S. Dietze, M.A. Casanova, R.
Kawase, B. Fetahu, and W. Nejdl., ESWC 2013 - 10th Extended
Semantic Web Conference, (May 2013).
A Scalable Approach for Efficiently Generating
Structured Dataset Topic Profiles, Fetahu, B., Dietze, S.,
Nunes, B. P., Casanova, M. A., Nejdl, W., 11th Extended
Semantic Web Conference (ESWC2014), Crete, Greece, (2014).
Dataset & entity linking: semantics of resources/datasets?
16 Stefan Dietze 31/07/14
<sioc:Item 2139393292>
<title>Planetary motion
& gravity</title>
…
</sioc:Item 2139393292>
Slideset
Pluto?
db:Pluto
(Dwarf
Planet)
db:Astrono-
mical Objects
db:Sun
Disambiguation/linking using background knowledge „Semantic relatetedness“ of resources?
db:Astronomy
17
<po:Programme519215>
<po:Series>Wonders of the Solar
System</po:Series>
<po:Episode>Emp. of the Sun</po:Episode>
<po:Actor>Brian Cox</po:Actor>
</po:Programme519215 >
Programme
<sioc:Item 2139393292>
<title>Planetary motion
& gravity</title>
…
</sioc:Item 2139393292>
Slideset
Video
Stefan Dietze 31/07/14
<yo:Video 8748720>
<dc:title>Pluto & the
Dwarf Planets</dc:title>
…
</yo:Video 8748720>
db:Pluto
(Dwarf
Planet)
db:Astrono-
mical Objects
db:Astronomy
Computation of connectivity scores between resources/entities
Method: combination of a
(i) semantic (graph-based) connectivity score (SCS) with
(ii) a Web co-occurence-based measure (CBM) (similar to NGD)
For (i): adaptation of Katz-Index from SNA for (linked) data graphs (considering path number and path lengths of transversal properties)
db:Sun
SCS = 0.32
CBM = 0.24
http://purl.org/vol/doc/
http://purl.org/vol/ns/
19/09/2013 18 Stefan Dietze
Combining a co-occurrence-based and a semantic
measure for entity linking, B. P. Nunes, S. Dietze, M.A.
Casanova, R. Kawase, B. Fetahu, and W. Nejdl., ESWC 2013
- 10th Extended Semantic Web Conference, (May 2013).
Entity linking: semantic relatedness
<sioc:Item 2139393292>
<title>Planetary motion
& gravity</title>
…
</sioc:Item 2139393292>
Slideset
<po:Programme519215>
<po:Series>Wonders of the Solar
System</po:Series>
<po:Episode>Emp. of the Sun</po:Episode>
<po:Actor>Brian Cox</po:Actor>
</po:Programme519215 >
Programme
<yo:Video 8748720>
<dc:title>Pluto & the
Dwarf Planets</dc:title>
…
</yo:Video 8748720>
Video
Entity linking: evaluation
31/07/14 19 Stefan Dietze
Evaluation based on USA Today News items (80.000 entity pairs)
Manually created gold standard (1000 entity pairs)
Baseline: Explicit Semantic Analysis (ESA)
=> CBM/SCS: „relatedness“; ESA: „similarity“
Precision/Recall/F1 for SCS, CBM, ESA.
Combining a co-occurrence-based and a semantic
measure for entity linking, B. P. Nunes, S. Dietze, M.A.
Casanova, R. Kawase, B. Fetahu, and W. Nejdl., ESWC 2013
- 10th Extended Semantic Web Conference, (May 2013).
db:Astro. Objects
Dataset Metadata
Stefan Dietze 31/07/14
Entity disambiguation & linking [ESWC13]
Topic profile extraction [WWW13, ESCW14]
db:Astronomy
db:Astro. Objects
Dataset
Catalog/Registry
yov:Video
<yo:Video …>
<dc:title>Pluto & the
Dwarf Planets</dc:title>
…
</yo:Video…>
Yovisto Video
Extracting representative metadata („topic profile“) for datasets
Ranking of most representative (DBpedia) categories (= topics); applied to all responsive LOD datasets
Scalability vs representativeness: sampling & ranking for good scalability/accuracy balance
A Scalable Approach for Efficiently Generating
Structured Dataset Topic Profiles, Fetahu, B.,
Dietze, S., Nunes, B. P., Casanova, M. A., Nejdl, W.,
11th Extended Semantic Web Conference
(ESWC2014), Crete, Greece, (2014).
Dataset profiling: what‘s the data about?
Dataset profiling: approach
Stefan Dietze 31/07/14
1. Sampling of resource instances (random sampling, weighted sampling, resource centrality sampling)
2. Entity and topic extraction (NER via DBpedia Spotlight, category mapping and expansion)
3. Normalisation and ranking (using graphical-models such as PageRank with Priors, HITS with Priors and K-Step Markov)
=> Result: weighted dataset-topic profile graph
A Scalable Approach for Efficiently Generating
Structured Dataset Topic Profiles, Fetahu, B.,
Dietze, S., Nunes, B. P., Casanova, M. A., Nejdl, W.,
11th Extended Semantic Web Conference
(ESWC2014), Crete, Greece, (2014).
Dataset profiling: exploring LOD datasets/topics in a nutshell http://data-observatory.org/lod-profiles/
Stefan Dietze 31/07/14
Automatic extraction of dataset “topics” [ESWC2014] => RDF/VoiD dataset profiles
Visualisation & exploration of dataset-topic graph (datasets, topics, relationships)
Includes all (responsive) datasets of LOD Cloud
Dataset profiling: results evaluation
Stefan Dietze 31/07/14
NDCG (averaged over all datasets) .
Datasets & Ground Truth
Yovisto, Oxpoints, LAK Dataset, Semantic Web Dogfood
Crowd-sourced topic indicators from datasets (keywords, tags)
Manual mapping to entities & category extraction (ranking according to frequency)
Baselines
1) LDA, 2) tf/idf (applied to entire datasets)
Topic extraction according to our approach, weighting/ranking based on term weight
Measure
NDCG @ rank l
Performance (time/NDCG) for different sampling strategies/sizes etc
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dbp:Category:Royal_Medal_winners
dbp:Category:1955_births dbp:Category:People_from_London
dbp:Category:Buzzwords
dbp:Category:Web_Services
dbp:Category:HTTP
dbp:Category:Unitarian_Universalists
dbp:Category:World_Wide_Web
What have these categories in common?
Stefan Dietze
31/07/14
Diversity of category profile for a single paper
Berners-Lee, Tim; Hendler, James, Ora Lassila (2001). "The Semantic Web". Scientific American Magazine.
person
document
dbp:Tim_Berners-Lee
dbp:Category:1955_births dbp:Category:People_from_London
dbp:Category:Buzzwords
dbp:Semantic_Web
dbp:Category:Semantic_Web
dbp:Category:Web_Services
dbp:Category:HTTP
dbp:Category:Unitarian_Universalists
first-level categories (dcterms:subject)
dbp:Category:World_Wide_Web
dbp:Category:Royal_Medal_winners
Stefan Dietze
31/07/14
http://data-observatory.org/led-explorer/
Type specific views on datasets/ categories
“Document” (foaf:document)
“Person “ (foaf:person)
“Course” (aaiso:course)
Currently applied to datasets in LinkedUp Catalog only (as schema mappings already available here)
Type-specific exploration of dataset categories
Stefan Dietze
May –September 2013 October 2013 – May 2014 May 2014 – October 2014
Series of Open Data Competitions to promote applications which exploit Linked Open Data
http://www.linkedup-challenge.org/
http://www.linkedup-project.eu/
LinkedUp Challenge: Linking Web Data (for Education)
“Vici” open just now
Final events at ISWC2014
Submission: 5 September
Conclusions & future work
Summary
Increasing amounts of data => require knowledge about nature and relationships of datasets
Profiling: scalable methods for extracting dataset metadata
Interlinking: connectivity of entities or datasets
Future work – LD evolution, preservation, consistency
In RDF graphs (eg LOD Cloud), „all“ nodes are connected
LD preservation: which datasets to preserve (entity „neighbourhood“)? => semantic relatedness
Link correctness in evolving LD: investigating impact of changes on link correctness
Application: informed preservation and enrichment strategies
31/07/14 37 Stefan Dietze
Thank you!
WWW See also (general)
http://linkedup-project.eu
http://linkededucation.org
http://data.l3s.de
http://purl.org/dietze
See also (data)
http://data.linkededucation.org
http://data.linkededucation.org/linkedup/catalog/
http://lak.linkededucation.org
31/07/14 38 Stefan Dietze
Besnik Fetahu (L3S)
Elena Demidova (L3S)
Bernardo Pereira Nunes (PUC Rio)
Marco Casanova (PUC Rio)
Luiz Andre Paes Leme (PUC Rio)
Giseli Lopes (PUC Rio)
Davide Taibi (CNR, IT)
Mathieu d’Aquin (Open University, UK)
and many more…
Acknowledgements