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. 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.
The concrete outcome of this research work is the following: (1) a website 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 & Architecture Thesaurus, Getty Thesaurus of Geographic Names, and Ordnance Survey), six of them are collaborative databases (Freebase, YAGO, DBpedia, Wikidata, LinkedGeoData, GeoNames), and the last one is about ecological observations based on expert and community collaborations (Encyclopedia of Life). We further compare datasets about geospatial entities with controlled vocabularies: Getty TGN, Open Names (Ordnance Survey), DBpediaPlace, 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. 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.
We then make use of structured records from a digital archive catalogue, and convert the records into semantically rich and interlinked resources on the Web. This is realized as a unified Linked Data catalogue to several digital archive collections. Our work results in a LOD catalogue available to the public at the website
. The following five parts are involved in realizing this website. A catalogue record, about a species of Pleione Formosana, is used throughout in the paper as an example to demonstrate the way we model, convert, and represent the semantics of a structured record.
Part 1: Exploring data reuse relations in a shared context -- We review our previous research about the Relation for Reuse Ontology (R4R). In particular, we provide mechanisms for reusing article, data, and code with some flexibility of encoding provenance and license information.
Part 2: Comparing two different data conversion approaches to providing LOD for an archive catalogue -- We show two different scenarios: (1) The LOD catalogue is converted directly from a relational database, and (2) the LOD catalogue is generated from a series of format conversions --- from XML to CSV, and then to RDF.
Part 3: Data profiling, cleaning and mapping -- We demonstrate format conversion processes, and we discuss the pros and cons of various ways in handling broken links in source datasets. In addition, we mapped and linked catalogue records to three external knowledge bases: GeoNames, Wikidata, and Encyclopedia of Life.
Part 4: Using CKAN (The Comprehensive Knowledge Archive Network) as a Linked Data platform -- We briefly introduce CKAN, an open source web-based data portal software package for curating and publishing datasets. CKAN provides data preview, search, and discovery, especially with regard to geospatial datasets. We built several extensions to CKAN in order to deposit, publish, browse, and search Linked Data. Various Linked Data representations of a catalogue record --- Turtle, RDF/XML, and JSON-LD --- can all be downloaded and reused.
Part 5: Designing ontologies for data representation and reuse -- We design an ontology voc4odw which includes the following 3 modules:
(1) The Core Model. It is comprise of a data model and a conceptual model. The data model represents key data structure and relation. It is a framework to illustrate data source, derivation, and provenance. The conceptual model incorporates SKOS Simple Knowledge Organization System; it also connects to key event concepts. The conceptual model allows for data contextualization using common and domain knowledge vocabularies.
(2) The Curation Model. It is responsible for disclosing the identification, classification, and publication of structured records at a curation platform, such as the classification of themes, the assignment of data identifiers, and the publication of datasets.
(3) A vocabulary voaf:Vocabulary. It is defined as "A vocabulary used in the Linked Data cloud", from the Vocabulary of a Friend
. This module is to relate the Core Model to external common vocabularies. Some hierarchy relations between different external vocabularies can be traced with this vocabulary.