=Paper=
{{Paper
|id=Vol-2180/paper-88
|storemode=property
|title=How to Maintain a Linked Data Cloud in a Deployed Semantic Portal
|pdfUrl=https://ceur-ws.org/Vol-2180/paper-88.pdf
|volume=Vol-2180
|authors=Mikko Koho,Esko Ikkala,Eero Hyvönen
|dblpUrl=https://dblp.org/rec/conf/semweb/KohoIH18
}}
==How to Maintain a Linked Data Cloud in a Deployed Semantic Portal==
https://ceur-ws.org/Vol-2180/paper-88.pdf
How to Maintain a Linked Data Cloud
in a Deployed Semantic Portal
Mikko Koho1 , Esko Ikkala1 , Eero Hyvönen1,2
1
Semantic Computing Research Group (SeCo), Aalto University, Finland and
2
HELDIG – Helsinki Centre for Digital Humanities, University of Helsinki, Finland
http://seco.cs.aalto.fi, http://heldig.fi
Problem Statement Plenty of data exists about the Second World War
(WW2), but the data is scattered in distributed databases, written in multi-
ple languages, and recorded in heterogeneous formats. Scenarios of this kind
are difficult for cultural heritage organizations and companies, where the data
is fragmented and all the different pieces are related to each other. A common
infrastructure is needed for the data, along with interfaces that allow citizens
to browse and study the data, and Digital Humanities researchers to use the
data easily for research. WW2 information is of great interest not only to histo-
rians, but to potentially hundreds of millions of citizens globally whose relatives
participated in the war, creating a global shared trauma.
Data values in different datasets are not directly interoperable as the meta-
data are not harmonized using shared vocabularies. Using shared vocabularies,
however, creates new kinds of challenges as changes in the shared vocabularies
need to be handled in the datasets using them [2]. For the shared vocabularies
to be sustainable, they need to be maintained by a responsible administrative
authority, in collaboration with the actual users of the vocabularies. The vocab-
ularies need to be expanded dynamically when new values are needed in them.
This kind of a complex scenario makes a promising use case for Linked Data
(LD), as various pieces of data can be connected in a flexible way. However,
maintaining LD brings in new technical challenges, like data transformation,
entity linking, and change propagation between graphs. The LD field is not
mature enough to provide tools that could be easily used by the domain experts
for the maintenance of Linked Data Clouds (LDC), dynamic systems of multiple
large interlinked graphs.
The WarSampo LDC Published in 2015, WarSampo [1] provides a dy-
namic ontology infrastructure for serving WW2 data as Linked Open Data
(LOD), and a growing collection of datasets, totaling ca 12 million triples. The
infrastructure is built to support integrating new datasets into WarSampo, by
extending both the domain ontologies and the data graphs. The work is done as
a collaboration between LD researchers and organizations possessing WW2 re-
lated data, such as the National Archives of Finland, the National Land Survey
of Finland, and the Finnish Defense Forces. WarSampo is a part of the global
international LOD cloud and was awarded the LODLAM Challenge Open Data
Prize in 2017. The WarSampo semantic portal3 builds upon the WarSampo data,
3
https://www.sotasampo.fi/en/
which is served on an open SPARQL endpoint4 . The portal provides different
perspectives to the knowledge base as customized web applications.
WarSampo was recently extended by a dataset of hundreds of war cemeteries
and thousands of photographs of them, and then by another dataset of about
4450 Finnish prisoners of war. The War Cemetery perspective was published in
November 2017 and got 57.000 users in one week, due to media coverage, which
set new demands for scalability. The Prisoners of War perspective is going to
be published in late 2018. In total, the WarSampo semantic portal was used by
130 000 users in 2017. The data service is based on a Fuseki SPARQL server on
a scalable cloud computing platform. The semantic portal is capable of handling
at least hundreds of concurrent users, accessing the data directly via SPARQL.
Lessons Learned Due to the interlinked graphs, the maintenance of the
data in RDF format is difficult. For example, the person instances are linked,
directly or indirectly, to everything in WarSampo. Modeling even just a person’s
basic information entails e.g. multiple events, such as birth, death, promotions,
and so on. So instead, the domain experts maintain the datasets in their native
formats (e.g. spreadsheets), which can then be reintegrated into WarSampo, as
needed. Reintegration is also used for solving the change propagations from one
graph to another. Sustainable long-term maintenance should be facilitated by
an administrative cultural heritage organization with domain knowledge, which
would need more mature and easy-to-use applications for data transformation,
entity linking, and LD maintenance.
With the LDC approach, we can harmonize inconsistent values in the data
integration phase, and mint URIs to new entities in DOs as needed. The LDC
can be analyzed and visualized as a whole, instead of focusing on individual
datasets. E.g., we can visualize the whole LDC on a map as a function of time.
There are other online services based on Finnish WW2 data, without semantic
technologies, such as the Casualties of War service of the National Archives and
Sotapolku5 . The services suffer from the lack of harmonization of data values,
missing linkage between entities, and lack of public data APIs.
Although integrating data into the LDC is more laborious than simpler ways
of publishing the data online, the result is an interlinked knowledge base, where
the graphs enrich each other through the linking, creating a whole that is greater
than the sum of its parts.
References
1. Hyvönen, E., Heino, E., Leskinen, P., Ikkala, E., Koho, M., Tamper, M., Tuominen,
J., Mäkelä, E.: WarSampo data service and semantic portal for publishing linked
open data about the Second World War history. In: The Semantic Web – Latest
Advances and New Domains (ESWC 2016). pp. 758–773. Springer-Verlag (2016)
2. Zablith, F., Antoniou, G., d’Aquin, M., Flouris, G., Kondylakis, H., Motta, E., Plex-
ousakis, D., Sabou, M.: Ontology evolution: a process-centric survey. The Knowledge
Engineering Review 30(1), 45–75 (2015)
4
http://ldf.fi/warsa/sparql
5
http://kronos.narc.fi/menehtyneet/, https://www.sotapolku.fi