MetaLink

A Travel Guide to the LOD Cloud

Wouter Beek (wouter@triply.cc), Joe Raad (j.raad@vu.nl), Erman Acar (erman.acar@vu.nl), Frank van Harmelen (frank.van.harmelen@vu.nl)

Triply B.V.

VU University Amsterdam

Linked Data Reuse

“Include links to other URIs, so that [data clients] can discover more things.”

4^th Linked Data Rule (source)

“Link your data to other data to provide context.”

5^th Linked Data star (source)

Linked Data is not possible without `owl:sameAs`

Corellary

Linked Data is not possible without formal logic.

Let's traverse the
LOD Cloud…

Start at node dbr:President_Barack_Obama.
Follow an incoming owl:sameAs link to go to node fb:m.05b6w1g.
Follow an outgoing owl:sameAs link to go to node dbr:Barack_Obama_Cabinet.

Oops! President Obama ≠ The Obama Cabinet

We need a Travel Guide that informs us where we can go (and what the risks are).

The percentage of incorrect `owl:sameAs` statements is…

2.8%

Hogan, A., Zimmermann, A., Umbrich, J., Polleres, A., Decker, S. 2012. “Scalable and Distributed Methods for Entity Matching, Consolidation and Disambiguation Over Linked Data Corpora”. Web Semantics: Science, Services and Agents on the World Wide Web Vol. 10, pp. 76–110.

4%

Raad, J. 2018. Identity Management in Knowledge Graphs. Ph.D. thesis, University of Paris-Saclay.

20%

Halpin, H., Hayes, P.J., McCusker, J.P., McGuinness, D.L., Thompson, H.S. 2010. “When owl:sameAs isn't the Same: An Analysis of Identity in Linked Data”. International Semantic Web Conference, pp. 305–320.

Detecting incorrect identity statements

Similarity of textual descriptions

J. Cuzzola, E. Bagheri, J. Jovanovic. 2015. “Filtering Inaccurate Entity Co-references on the Linked Open Data” International DEXA Conference, pp. 128–143.

Violations of UNA heuristic

G. de Melo. 2013. “Not Quite the Same: Identity Constraints for the Web of Linked Data” AAAI.
A. Valdestilhas, T. Soru, A. Ngomo. 2017. “Cedal: Time-efficient Detection of Erroneous Links in Large-scale Link Repositories” International Conference on Web Intelligence, pp. 106–113.

Detection of logical inconsistencies

A. Hogan, A. Zimmermann, J. Umbrich, A. Polleres, S. Decker. 2012. “Scalable and Distributed Methods for Entity Matching, Consolidation and Disambiguation over Linked Data Corpora” Web Semantics, Vol. 10, pp. 76–110.
L. Papaleo, N. Pernelle, F. Saïs, C. Dumont. 2014. “Logical Detection of Invalid sameAs Statements in RDF Data” EKAW, pp. 373–384.

Network metrics

C. Guéret, P. Groth, C. Stadler, J. Lehmann. 2012. “Assessing Linked Data Mappings Using Network Measures” Extended Semantic Web Conference, pp. 87–102

Crowd-sourcing

M. Acosta, A. Zaveri, E. Simperl, D. Kontokostas, S. Auer, J. Lehmann. 2013. “Crowd-sourcing Linked Data Quality Assessment” International Semantic Web Conference, pp. 260–276

Overview paper

J. Raad, N. Pernelle, F. Saïs, W. Beek, F. van Harmelen. 2019. “The sameAs Problem: A Survey on Identity Management in the Web of Data” (under review) (link)

MetaLink Requirements

Scalable

Applicable to the whole LOD Cloud (billions of triples).

Ordered

Distinguish between subject/from and object/to nodes.

Modular

Plug it into any Linked Dataset.

Standards-compliant

LD clients must be able to use it.

Broadly applicable

Cover a broad range of research goals and applications.

Low-cost

Every researcher should be able to affort it.

MetaLink Concepts

Partitions

Equivalence Sets
Communities (Louvain algorithm, J. Raad, Beek, F. van Harmelen, N. Pernelle, F. Saïs. 2018. “Detecting Erroneous Identity Links on the Web using Network Metrics” ISWC)

Links

Identity Statements

Explicit: appear in the LOD Cloud.
Implicit: derived from the explicit identity statements.

Community links

Intra-community links (within)
Inter-community links (from/to)

Explicit identity statements for ‘Barack Obama’

‘Barack Obama’ after community detection

Communities correspond to roles:

person
senator
president
government

MetaLink vocabulary

MetaLink Quantified

Class	№ instances
`meta:IdentityStatement`	556,152,454
`meta:Community`	55,697,160
`meta:EquivalenceSet`	48,999,148
№ implicit identity statements	35,201,120,188

Property	№ triples
`meta:error`	556,152,454
`meta:community`	410,706,139
`meta:fromCommunity`	145,446,315
`meta:toCommunity`	145,446,315
`meta:cardinality`	48,999,148
`meta:equivalenceSet`	55,697,160
`meta:cardinality`	48,999,148
Total	4,352,602,480

Online publication

MetaLink: https://krr.triply.cc/krr/metalink (example)
LOD-a-lot (Fernandez 2017): https://krr.triply.cc/krr/lod-a-lot
LOD-a-lot + MetaLink: https://krr.triply.cc/krr/lod-a-lot-metalink

Use case 1: Follow-Your-Nose

Problem

fb:m.05b6w1g owl:sameAs dbr:President_Barack_Obama. # ←
fb:m.05b6w1g owl:sameAs dbr:Barack_Obama_Cabinet.   # →

Oops, a lightweight client bumps into inconsistency after 2 hops…

Solution

select ?error {
  [ rdf:subject fb:m.05b6w1g;
    rdf:object dbr:President_Barack_Obama;
    meta:error ?error ].
}

With MetaLink, a lightweight client can probe how safe an owl:sameAs link is (run online).

Use case 2: Question Answering

Through which countries does the Yenisei river flow? (Lopez et al. 2013)

select distinct ?uri ?string {
  dbr:Yenisei_River owl:sameAs*/dbp:country/owl:sameAs* ?uri.
  optional {
    ?uri rdfs:label ?string.
    filter(lang(?string) = "en")
  }
}

Returns over 30K results, including hundreds of unrelated geographic places, the concept of creative writing, and the mythical creature Gorgon.

Setting error value < 0.3 only returns identifiers for Russia and Mongolia (the correct answers).

Use case 2: Question Answering

What are the band members of ABBA? (Buikstra et al. 2011)

Result	≤ 1.0	≤ 0.8	≤ 0.6	≤ 0.4	≤ 0.2	≤ 0.0
Björn Ulvaeus (band member)	28	8	8	3	2	2
Agnetha Fältskog (band member)	26	4	4	2	1	1
Anni-Frid Lyngstad (band member)	9	3	3	2	1	1
Benny Andersson (band member)	6	2	2	1	1	1
Ola Brukert (drummer)	3	2	2	1	1	1
Agnetha Ulvaeus (Agnetha F. married name)	2	0	0	0	0	0
Stig Andersson (band manager)	9	4	4	1	1	1
Gert van der Graaf (stalker of Agnetha Fältskog)	2	0	0	0	0	0
Benny Anderssons Orkester (new band)	5	3	3	0	0	0
Stig Andersson (sportsman)	2	2	2	0	0	0

Results of the ABBA band member query using different error degrees in MetaLink.

Use case 3: Fuzzy Reasoning

Fuzzy identity function (t-conorm): commutative, monotonic, associative (compositionality).

This still allows for Linked Data reuse: see i₁

This even allows for better Linked Data reuse: see i₃

Use case 4: Link Error Detection for Subsets

Apply other, more computationally intensive, approaches for links with error values [0.3,0.7].

Use case 5: Link Error Benchmarking

Current sets are small / dataset-specific: DBpedia-based, OAEI.

MetaLink

A Travel Guide to the LOD Cloud

https://krr.triply.cc/krr/metalink

Wouter Beek (wouter@triply.cc), Joe Raad (j.raad@vu.nl), Erman Acar (erman.acar@vu.nl), Frank van Harmelen (frank.van.harmelen@vu.nl)

Triply B.V.

VU University Amsterdam

MetaLink

A Travel Guide to the LOD Cloud

Linked Data Reuse

Linked Data is not possible without owl:sameAs

Corellary

Let's traverse theLOD Cloud…

The percentage of incorrect owl:sameAs statements is…

Detecting incorrect identity statements

MetaLink Requirements

MetaLink Concepts

Explicit identity statements for ‘Barack Obama’

‘Barack Obama’ after community detection

MetaLink vocabulary

MetaLink Quantified

Online publication

Use case 1: Follow-Your-Nose

Problem

Solution

Use case 2: Question Answering

Use case 2: Question Answering

Use case 3: Fuzzy Reasoning

Use case 4: Link Error Detection for Subsets

Use case 5: Link Error Benchmarking

MetaLink

A Travel Guide to the LOD Cloud

Linked Data is not possible without `owl:sameAs`

Let's traverse the
LOD Cloud…

The percentage of incorrect `owl:sameAs` statements is…