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Wednesday, 5 September 2018

Revisit: Reuse of Structured Data: Semantics, Linkage, and Realization (1)


RESEARCH HIGHLIGHTS: 

# An old record is not a data but now defined as a new semantic dataset. 
  i.e. its triples, graphs, links, file formats ...
  i.e. its revised, vocabulary encoded versions ...
  ex. data:d2148340 a dcat:dataset. #files:json-ld, ttl, XML

# A new method to curate, publish & visualize LOD graphs via CKAN portal. 
  i.e. two models for one dataset published in two views.
  ex. data:d2148340 a dcat:dataset.   # Dublin Core @schema1
  ex. data:d2148340 a data:Refined. # more semantics@schema2

# Validation & Reproducibility: Provenance and Contexts are in details. 

Introduction

In order to enhance the reuse value of existing datasets, it is now becoming a general practice to add semantic links among the records in a dataset, and to link these records to external resources. The enriched datasets are published on the Web for both the human and the machine to consume and re-purpose. 


Open Data Web (data.odw.tw)
In the paper, we make use of publicly available structured records from a digital archive catalogue, and we demonstrate a principled approach to converting the records into semantically rich and interlinked resources for all to reuse. 

While exploring the various issues involved in the process of reusing and re-purposing existing datasets, we review the recent progress in the field of Linked Open Data (LOD), and examine twelve well-known knowledge bases built with a Linked Data approach. We also discuss the general issues of data quality, metadata vocabularies, and data provenance.


Different Contexts in Different Data Curation Phases

The concrete outcome of this research work is the following: 
  1. a website/repository (Open Data Web) that hosts more than 840,000 semantically enriched catalogue records across multiple subject areas, 
  2. a lightweight ontology voc4odw for describing data reuse and provenance, among others, and 
  3. a set of open source software tools available to all to perform the kind of data conversion and enrichment we did in this research. We have used and extended CKAN (The Comprehensive Knowledge Archive Network) as a platform to host and publish Linked Data. 
Our extensions to CKAN is open sourced as well. As the records we have drawn from the originally catalogue are released under the Creative Commons licenses, the semantically enriched resources we now re-publish on the Web are free for all to reuse as well. Review of Twelve Knowledge Bases We begin by first examine twelve knowledge bases built with a Linked Data approach. 

Five of them are built by domain knowledge experts (OpenCyc, Getty Art and Architecture Thesaurus (AAT), Getty Thesaurus of Geographic Names (TGN), and Ordnance Survey/ Open Names), six of them are collaborative databases (FreebaseYAGO, DBpediaWikidataLinkedGeoDataGeoNames), and the last one is about ecological observations based on expert and community collaborations (Encyclopedia of Life/ EOL/ TraitBank). We further compare datasets about geospatial entities with controlled vocabularies: Getty TGN, Open Names (Ordnance Survey), DBpediaPlace*(instances of dbo:Place), LinkedGeoData, and GeoNames.

To make good reuse of structured data, ones need to first deal with the problem of data quality. Currently there exist different evaluation criteria, with various techniques for measuring the quality of information, data, metadata, and Linked Data. 


LOD Knowledge Bases/Graphs (2016/11/06 sparql query results) /
LOD Knowledge Graph
since
organization
domain
resource
triples
update frequency
data source


Expert Lead
(top down)
2008
business
cross-domain
41,029
2,412,520
over one year
owner
2014
business
art &
45,327
13,259,890
3-5 times a year
owner
2014
business
place name
2,495,100
204,614,290
owner

2010
government
geography

2,938,707
58,377,209
depending
owner
2015
government
place name
925,157
21,360,688
twice a year



Collective
Collaboration
(bottom up)
2008
business
cross-domain
49,947,799
3,124,791,156
close din 2015
2007
university
cross-domain
5,130,031
1,001,461,786
over one year
2007
university
cross-domain
5,109,890
402,086,316
about one year/
some in Live.
DBpediaPlace*
2007
university
place (name)
816,252
53,895,946
2012
NGO
cross-domain
19,367,201
1,371,170,022
real time
2010
university
geography
> 3 billion
1,384,887,500
about one year
2010
NGO
place name
>6.2 million
93,896,732
real Time
data collaboration/ partly integrated with others
Mix Mode
2014
association
biodiversity
10,753,384
359,292,712
statistic data/ a week
research databases integration/ partly collaborated


We review four papers on data quality and systematically compare their evaluation criteria. Moreover, data provenance --- contextual metadata about the source and use of data --- has proven to be fundamental for assessing authenticity, enabling trust, and allowing reproducibility. Thus, we examine key mechanisms of data provenance before we move forward to discussing LOD applications.