Linked data

After the digitized material of the persons, countries/subjects and companies archives of the 20th Century Press archives had been made available via Wikidata, now the last part from the wares archive has been added.

This ware archive is about products and commodities. Founded in 1908 at the Hamburg "Kolonialinstitut" (colonial institute) as part of the larger press archives, it was maintained by the Hamburg Institute of International Economics (HWWA) until 1998. Now it is part of the cultural heritage, which ZBW has decided to make freely available to the largest possible extend, as part of its Open Access and Open Science policy. While the digitized pages are provided reliably under stable URIs on https://pm20.zbw.eu, the metadata has been donated to Wikidata.

For each ware (e.g., coal), there was a folder - or a series of folders - about the ware or commodity in general, its cultivation, extraction or production, trade, industry, and utilization. For each country, for which this ware was important, separate folders were created. For some important wares, such as coal, that amounted to thousands of documents in the general section, as well as for traditional production countries like the UK, but also more ephemeral deposits like the Philippines. In total, almost 37,000 press articles about coal production and consumption in the first half of the last century are accessible online.

The coverage of the archives (overview) extends to quite special sectors, such as amber or cotton machines. Sadly, only a small part of the commodities/wares archives is freely available on the web. The labour-intensive preparation of the folders was inevitable due to intellectual property law, but could be only achieved for one ninth of the documents. The rest of this material up to 1946, and another time slice with 600,000 pages until 1960, can be accessed as digitized microfilms on the ZBW premises (film overview 1908-1946, 1947-1960, systematic structure). Additionally, 15,000 microfiches cover the full time range of the archives until 1998.

Integration of the metadata into Wikidata

For the country category structure of the archive we used, as in the countries/subjects archive, existing Wikidata items. Most of the commodities and wares categories were also already present as items, and we matched and linked them via OpenRefine. Only a handfull of special, artifical categories (like Axe, hatchet, hammer) had to be created.

We then, for each folder of the archive, built an item in Wikidata, defined by a commodity/ware and a country category, and linking to the according folder in the press archives (e.g., Coal : United States of America). For the general, non-country specific folders, the commodities/ware category was combined with the item for "world", as in Banana : World. The diversity of the archive's topics in Wikidata shows up

in a colorful picture (live query), providing an entry point into the archive.

In total, 2891 items representing PM20 ware/category folders were created. As this last archive, the integration of the 20th Century Press Archives' metadata into Wikidata is completed. Every folder of the archives is represented in Wikidata and links to digitized press clippings and other material about its topic. How these Wikidata items can be used in queries and applications will be the subject of another ZBW labs blog entry.

ZBW is donating a large open dataset from the 20th Century Press Archives to Wikidata, in order to make it better accessible to various scientific disciplines such as contemporary, economic and business history, media and information science, to journalists, teachers, students, and the general public.

The 20th Century Press Archives (PM20) is a large public newspaper clippings archive, extracted from more than 1500 different sources published in Germany and all over the world, covering roughly a full century (1908-2005). The clippings are organized in thematic folders about persons, companies and institutions, general subjects, and wares. During a project originally funded by the German Research Foundation (DFG), the material up to 1960 has been digitized. 25,000 folders with more than two million pages up to 1949 are freely accessible online.  The fine-grained thematic access and the public nature of the archives makes it to our best knowledge unique across the world (more information on Wikipedia) and an essential research data fund for some of the disciplines mentioned above.

The data donation does not only mean that ZBW has assigned a CC0 license to all PM20 metadata, which makes it compatible with Wikidata. (Due to intellectual property rights, only the metadata can be licensed by ZBW - all legal rights on the press articles themselves remain with their original creators.) The donation also includes investing a substantial amount of working time (during, as planned, two years) devoted to the integration of this data into Wikidata. Here we want to share our experiences regarding the integration of the persons archive metadata.

At 27th and 28th of October, the Kick-off for the "Kultur-Hackathon" Coding da Vinci is held in Mainz, Germany, organized this time by GLAM institutions from the Rhein-Main area: "For five weeks, devoted fans of culture and hacking alike will prototype, code and design to make open cultural data come alive." New software applications are enabled by free and open data.

For the first time, ZBW is among the data providers. It contributes the person and company dossiers of the 20th Century Press Archive. For about a hundred years, the predecessor organizations of ZBW in Kiel and Hamburg had collected press clippings, business reports and other material about a wide range of political, economic and social topics, about persons, organizations, wares, events and general subjects. During a project funded by the German Research Organization (DFG), the documents published up to 1948 (about 5,7 million pages) had been digitized and are made publicly accessible with according metadata, until recently solely in the "Pressemappe 20. Jahrhundert" (PM20) web application. Additionally, the dossiers - for example about Mahatma Gandhi or the Hamburg-Bremer Afrika Linie - can be loaded into a web viewer.

As a first step to open up this unique source of data for various communities, ZBW has decided to put the complete PM20 metadata* under a CC-Zero license, which allows free reuse in all contexts. For our Coding da Vinci contribution, we have prepared all person and company dossiers which already contain documents. The dossiers are interlinked among each other. Controlled vocabularies (for, e.g., "country", or "field of activity") provide multi-dimensional access to the data. Most of the persons and a good share of organizations were linked to GND identifiers. As a starter, we had mapped dossiers to Wikidata according to existing GND IDs. That allows to run queries for PM20 dossiers completely on Wikidata, making use of all the good stuff there. An example query shows the birth places of PM20 economists on a map, enriched with images from Wikimedia commons. The initial mapping was much extended by fantastic semi-automatic and manual mapping efforts by the Wikidata community. So currently more than 80 % of the dossiers about - often rather prominent - PM20 persons are linked not only to Wikidata, but also connected to Wikipedia pages. That offers great opportunities for mash-ups to further data sources, and we are looking forward to what the "Coding da Vinci" crowd may make out of these opportunities.

Technically, the data has been converted from an internal intermediate format to still quite experimental RDF and loaded into a SPARQL endpoint. There it was enriched with data from Wikidata and extracted with a construct query. We have decided to transform it to JSON-LD for publication (following practices recommended by our hbz colleagues). So developers can use the data as "plain old JSON", with the plethora of web tools available for this, while linked data enthusiasts can utilize sophisticated Semantic Web tools by applying the provided JSON-LD context. In order to make the dataset discoverable and reusable for future research, we published it persistently at zenodo.org. With it, we provide examples and data documentation. A GitHub repository gives you additional code examples and a way to address issues and suggestions.

* For the scanned documents, the legal regulations apply - ZBW cannot assign licenses here.

The Journal of Economic Literature Classification Scheme (JEL) was created and is maintained by the American Economic Association. The AEA provides this widely used resource freely for scholarly purposes. Thanks to André Davids (KU Leuven), who has translated the originally English-only labels of the classification to French, Spanish and German, we provide a multi-lingual version of JEL. It's lastest version (as of 2017-01) is published in the formats RDFa and RDF download files. These formats and translations are provided "as is" and are not authorized by AEA. In order to make changes in JEL tracable more easily, we have created lists of inserted and removed JEL classes in the context of the skos-history project.

Wikidata is a large database, which connects all of the roughly 300 Wikipedia projects. Besides interlinking all Wikipedia pages in different languages about a specific item – e.g., a person -, it also connects to more than 1000 different sources of authority information.

The linking is achieved by a „authority control“ class of Wikidata properties. The values of these properties are identifiers, which unambiguously identify the wikidata item in external, web-accessible databases. The property definitions includes an URI pattern (called „formatter URL“). When the identifier value is inserted into the URI pattern, the resulting URI can be used to look up the authoritiy entry. The resulting URI may point to a Linked Data resource - as it is the case with the GND ID property. This, on the one hand, provides a light-weight and robust mechanism to create links in the web of data. On the other hand, these links can be exploited by every application which is driven by one of the authorities to provide additional data: Links to Wikipedia pages in multiple languages, images, life data, nationality and affiliations of the according persons, and much more.

Wikidata item for the Indian Economist Bina Agarwal, visualized via the SQID browser

We are happy to announce that we have updated our EconStor LOD dump. This dataset now comprises 108k metadata records provided with Semantic Web URIs and partially linked to external datasets like STW and JEL.

The "Integrated Authority File" (Gemeinsame Normdatei, GND) of the German National Library (DNB), the library networks of the German-speaking countries and many other institutions, is a widely recognized and used authority resource. The authority file comprises persons, institutions, locations and other entity types, in particular subject headings. With more than 134,000 concepts, organized in almost 500 subject categories, the subjects part - the former "Schlagwortnormdatei" (SWD) - is huge. That would make it a nice resource to stress-test SKOS tools - when it would be available in SKOS. A seminar at the DNB on requirements for thesauri on the Semantic Web (slides, in German) provided another reason for the experiment described below.

“What’s new?” and “What has changed?” are questions users of Knowledge Organization Systems (KOS), such as thesauri or classifications, ask when a new version is published. Much more so, when a thesaurus existing since the 1990s has been completely revised, subject area for subject area. After four intermediately published versions in as many consecutive years, ZBW's STW Thesaurus for Economics has been re-launched recently in version 9.0. In total, 777 descriptors have been added; 1,052 (of about 6,000) have been deprecated and in their vast majority merged into others. More subtle changes include modified preferred labels, or merges and splits of existing concepts.

Since STW has been published on the web in 2009, we went to great lengths to make change traceable: No concept and no web page has been deleted, everything from prior versions is still available. Following a presentation at DC-2013 in Lisbon, I've started the skos-history project, which aims to exploit published SKOS files of different versions for change tracking. A first beta implementation of Linked-Data-based change reports went live with STW 8.14, making use of SPARQL "live queries" (as described in a prior post). With the publication of STW 9.0, full reports of the changes are available. How do they work?

SPARQL queries are a great way to explore Linked Data sets - be it our STW with it's links to other vocabularies, the papers of our repository EconStor, or persons or institutions in economics as authority data. ZBW therefore offers since a long time public endpoints. Yet, it is often not so easy to figure out the right queries. The classes and properties used in the data sets are unknown, and the overall structure requires some exploration. Therefore, we have started collecting queries in our new SPARQL Lab, which are in use at ZBW, and which could serve as examples to deal with our datasets for others.

A major challenge was to publish queries in a way that allows not only their execution, but also their modification by users. The first approach to this was pre-filled HTML forms (e.g. http://zbw.eu/beta/sparql/stw.html). Yet that couples the query code with that of the HTML page, and with a hard-coded endpoint address. It does not scale to multiple queries on a diversity of endpoints, and it is difficult to test and to keep in sync with changes in the data sets. Besides, offering a simple text area without any editing support makes it quite hard for users to adapt a query to their needs.

And then came YASGUI, an "IDE" for SPARQL queries. Accompanied by the YASQE and YASR libraries, it offers a completely client-side, customable, Javascript-based editing and execution environment. Particular highlights from the libraries' descriptions include:

Large library collections, and more so portals or discovery systems aggregating data from diverse sources, face the problem of duplicate content. Wouldn't it be nice, if every edition of a work could be collected beyond one entry in a result set?

The WorldCat catalogue, provided by OCLC, holds more than 320 million bibliographic records. Since early in 2014, OCLC shares its 197 million work descriptions as Linked Open Data: "A Work is a high-level description of a resource, containing information such as author, name, descriptions, subjects etc., common to all editions of the work. ... In the case of a WorldCat Work description, it also contains [Linked Data] links to individual, oclc numbered, editions already shared in WorldCat." The works and editions are marked up with schema.org semantic markup, in particular using schema:exampleOfWork/schema:workExample for the relation from edition to work and vice versa. These properties have been added recently to the schema.org spec, as suggested by the W3C Schema Bib Extend Community Group.

ZBW contributes to WorldCat, and has 1.2 million oclc numbers attached to it's bibliographic records. So it seemed interesting, how many of these editions link to works and furthermore to other editions of the very same work.

ZBW Labs now uses DBpedia resources as tags/categories for articles and projects. The new Web Taxonomy plugin for DBpedia Drupal module (developed at ZBW) integrates DBpedia labels, stemming from Wikipedia page titles, via a comfortable autocomplete plugin into the authoring process. On the term page (example), further information about a keyword can be obtained by a link to the DBpedia resource. This at the same time connects ZBW Labs to the Linked Open Data Cloud.

The plugin is the first one released for Drupal Web Taxonomy, which makes LOD resources and web services easily available for site builders. Plugins for further taxonomies are to be released within our Economics Taxonomies for Drupal project.

From the beginning, our econ-ws (terminology) web services for economics produce tabular output, very much like the results of a SQL query. Not a surprise - they are based on SPARQL, and use the well-defined table-shaped SPARQL 1.1 query results formats in JSON and XML, which can be easily transformed to HTML. But there are services, whose results not really fit this pattern, because they are inherently tree-shaped. This is true especially for the /combined1 and the /mappings service. For the former, see our prior blog post; an example of the latter may be given here: The mappings of the descriptor International trade policy are (in html) shown as:

That´s far from perfect - the "concept" and "prefLabel" entries of the source concept(s) of the mappings are identical over multiple rows.

As a laboratory for new, Linked Open Data based publishing technologies, we now develop the ZBW Labs web site as a Semantic Web Application. The pages are enriched with RDFa, making use of Dublin Core, DOAP (Description of a Project) and other vocabularies. The schema.org vocabulary, which is also applied through RDFa, should support search engine visibility.

With this new version we aim at a playground to test new possibilities in electronic publishing and linking data on the web. At the same time, it facilitates editorial contributions from project members about recent developments and allows comments and other forms of participation by web users.

As it is based on Drupal 7, RDFa is "build-in" (in the CMS core) and is easy done by configuration on a field level. Enhancements are made through the RDFx. Schema.org and SPARQL Views modules. A lot of other ready-made components in Drupal (most noteworthy the Views and the new Entity Reference modules) make it easy to provide and interlink the data items on the site. The current version of Zen theme enables the HTML 5 and the use of RDFa 1.1, and permits a responsive design for smartphones and pads.