Linked data: permanence

The following post is an excerpt from my thesis entitled Linked open data for public sector information.
Linked data principles enforce separation of data and applications, which promotes permanence. Modelling linked data is modelling without a context of use [1, p. 11]. When designing a data model for linked data, its creators abstract away from particular uses the data may get, such as in specific applications. Such design principle results in an application-agnostic data model that is not tightly coupled with any type of use that might be intended for the data. As a result, the data supports a wide range of unintended and unforeseen uses. Given the data is decoupled from applications using it, it needs not to be changed when the implementation of interfaces mediating it changes. Moreover, the software used for publishing or consuming linked data is in most cases open source and thus needs not to be changed if a vendor providing it changes. Even if there was no support for these open source solutions, data formats used for linked data have open specificiations that may be re-implemented by anyone.
Established design patterns for linked data promote persistent URIs providing long-lasting access points [2, p. 5]. Several of the best practices for minting URIs contribute to their persistence. URIs should not be made session-specific, in which case they cannot be used for re-identifying the requested resources after the session expires. URIs should be made implementation-agnostic because if they depend on an implementation they cannot outlast it. Therefore, URIs should not be cluttered with implementation details, such as file type suffixes (e.g., .php). A technique that further decouples URIs from the way they are dereferenced is to introduce a layer of indirection by using a service such as http://purl.org to redirect URIs to URLs that serve their representations. However, ultimately the persistence of URIs is proportional to the commitment of institutions maintaining them.

References

1. WOOD, David (ed.). Linking government data. Heidelberg: Springer, 2011. ISBN 978-1-4614-1766-8.
2. Designing URI sets for the UK public sector: a report from the Public Sector Information Domain of the CTO Council’s Cross-Government Enterprise Architecture [online]. 2009 [cit. 2012-02-26]. Available from WWW: http://www.cabinetoffice.gov.uk/sites/default/files/resources/designing-URI-sets-uk-public-sector.pdf