This document discusses three use cases for preserving linked data: 1) archiving and retrieving RDF data from DBpedia at specific points in time, 2) rendering archived DBpedia data as web pages, and 3) reconstructing the functionality of DBpedia's SPARQL endpoint for past times. It also presents exercises for each use case and discusses additional technical, organizational, and economic issues around long-term linked data preservation.

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Preserving Linked DataHands-on use cases
José María García
ESWC Summer School 2014

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Outline
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Use case 1
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Use case 2
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Use case 3
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Additional technical/organizational/economical issues for preserving LD
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Use case 1 –RDF data archiving and retrieval
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DBpedia data (in RDF format, or Tables-CSV format) is archived and the user requests specific data (or the entire dataset) as it was at a specific date in the past.
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The preservation mechanism must be able to provide the requested data in RDF (or Table) format.
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Timestamps specifying the interval that the data was valid (i.e., dates that the data was created or modified for the last time before the date specified into the user request, and first modification or deletion date after that date) are a desirable feature of the mechanism.
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Use case 1 -Exercise
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Browse through DBpedia archives at http://wiki.dbpedia.org/Downloads
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Find the date when the last update was generated. Is it concrete enough?
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Can you use the available files to reconstruct DBpedia?
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Look at the links to other datasets. Are the datasets also available there?
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Focus on Amsterdam Museum Data dataset
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Can you download the dataset to reconstruct DBpedia and its link to this dataset?
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Can you retrieve the exact version of the dataset that was linked to DBpedia 3.9?
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Now look at previous versions of DBpedia, such as 3.7
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Which differences you can find?
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Is it also possible to reconstruct this previous version? What about linked datasets?
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What about other datasets?
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Look for Bricklink and GeoNames datasets, for instance.
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Are they accessible?
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Can you retrieve previous versions?
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Try out DBpedia live at http://live.dbpedia.org/
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Use case 1 -Extension
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Retrieving data for a specific time interval, e.g., 2010-2012, instead of a specific date is a more complex case since all versions of the data and their corresponding validity intervals with respect to the request interval must be returned.
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Currently complex requests involving intervals are not handled by the DBpedia archiving mechanism. RDF data containing links to other LOD for specific time points can be retrieved, but the content of links to external LOD is not preserved.
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Use case 1 –Discussion
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Are DBpedia archiving measures sufficient to ensure its long-term preservation?
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Who is responsible for archiving external datasets?
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Up to which link depth datasets should be archived/preserved?
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Exercise 1 –DBpedia 3.9
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Exercise 1 –DBpedia 3.9 links to datasets
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Exercise 1 –Amsterdam Museum Data
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Exercise 1 –Amsterdam Museum Data dumps
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Exercise 1 –DBpedia 3.7
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Exercise 1 –DBpedia 3.7 links to datasets
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Exercise 1 –DBpedia to Bricklink links
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Exercise 1 –Bricklink dataset
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Exercise 1 –GeoNames data
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Exercise 1 –GeoNames dumps download
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Exercise 1 –GeoNames premium service
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Use case 2 –Rendering data as Web page
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User requests the DBpedia data for a specific topic at a given temporal point or interval presented in a Web page format
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The preservation mechanism should be able to return the data in RDF format and in case description is modified during the given interval all corresponding descriptions, the intervals that each one distinct description was true, modification history, differences between versions and editors should be returned as in the first use case.
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Rendering requested data as a Web page will introduce the following problem: can the functionality of external links be preserved and supported as well or not?
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Currently rendering software is not part of the preservation mechanism, although using a standard representation (RDF) minimizes the risk of not been able to render the data in the future.
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Use case 2 –Exercise & Discussion
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Check some DBpedia pages, such as http://dbpedia.org/page/Semantic_Web
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Look for information on provenance and revision
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Are previous versions available for the user?
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Is it easy to add modification history, diffs, etc.?
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Should we preserve the rendering mechanism along with the data dumps?
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Exercise 2 –DBpedia entity rendered for web
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Use case 3 –SPARQL endpoint functionality
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Reconstruct the functionality of the DBpedia SPARQL endpoint at a specific temporal point in the past.
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Specifying both the query and the time point (this use case can be extended by supporting interval queries as in use case 1 and 2 before) . There are different kinds of queries that must be handled corresponding to different use cases:
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Queries spanning into RDF data into DBpedia dataset only
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Queries spanning into DBpedia dataset and datasets directly connected to the DBpedia RDF dataset (e.g., Geonames)
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Queries spanning into DBpedia data and to external datasets connected indirectly with DBpedia (i.e., through links to datasets of case b).
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Currently SPARQL end-point functionality is not directly preserved, i.e., the users must retrieve the data and use their own SPARQL end-point to query them.
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Use case 3 –Extension
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Currently SPARQL end-point functionality is not directly preserved, i.e., the users must retrieve the data and use their own SPARQL end-point to query them.
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Then, they will be able to issue queries of type (a) above, but not queries of type (b) when the content of external links is requested.
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Also requests of type (c) cannot be handled by the current preservation mechanism
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Use case 3 –Exercise & Discussion
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Look at DBpedia SPARQL endpoint http://dbpedia.org/sparql
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Try some SPARQL query, such as:
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SELECT ?group WHERE {
?group a <http://schema.org/MusicGroup>.
?group dbpprop:origin?origin .
FILTER contains(str(?origin), "Crete")}
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How can we access previous datasets in the SPARQL-endpoint?
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Can a SPARQL-endpoint be reconstructed from the archived datasets?
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Should SPARQL endpoint be preserved along with the data?
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Exercise 3
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Technical issues
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OAIS model compliance
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Standard for archiving
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Other desirable standards to be used (DCAT, PROV…)
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Data ingestion
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What amount of data should be preserved?
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Implicit semantics
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Inferred/derived knowledge
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Preserving URIs dereferencability
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Bricklinkdataset problem
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Dealing with changes
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When to update an archive
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DBpedia Live
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Organizational issues
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Stakeholders
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Who is interested in LD preservation?
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E.g. DBpedia association, users…
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Scope of preservation systems
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Which datasets are worth to preserve?
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Responsibilities
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Who should take care of long-term preservation?
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Data curators? Users? Government?
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Economical issues
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Sustainability
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Business plans should be created to offer long-term preservation
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Is it viable to preserve Linked Data?
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Intellectual Property Rights and Licenses
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Open data licenses help
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What about proprietary data?
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Liability and obligations
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Thanks!
Any questions?
Drop me an email at jose.garcia@sti2.at
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