Abstract Modelling of Digital Identifiers

Abstract

Discussion of digital identifiers, and persistent identifiers in particular, has often been confused by differences in underlying assumptions and approaches. To bring more clarity to such discussions, the PILIN Project has devised an abstract model of identifiers and identifier services, which is presented here in summary. Given such an abstract model, it is possible to compare different identifier schemes, despite variations in terminology; and policies and strategies can be formulated for persistence without committing to particular systems. The abstract model is formal and layered; in this article, we give an overview of the distinctions made in the model. This presentation is not exhaustive, but it presents some of the key concepts represented, and some of the insights that result.The main goal of the Persistent Identifier Linking Infrastructure (PILIN) project [1] has been to scope the infrastructure necessary for a national persistent identifier service. There are a variety of approaches and technologies already on offer for persistent digital identification of objects. But true identity persistence cannot be bound to particular technologies, domain policies, or information models: any formulation of a persistent identifier strategy needs to outlast current technologies, if the identifiers are to remain persistent in the long term.For that reason, PILIN has modelled the digital identifier space in the abstract. It has arrived at an ontology [2] and a service model [3] for digital identifiers, and for how they are used and managed, building on previous work in the identifier field [4] (including the thinking behind URI [5], DOI [6], XRI [7] and ARK [8]), as well as semiotic theory [9]. The ontology, as an abstract model, addresses the question ‘what is (and isn’t) an identifier?’ and ‘what does an identifier management system do?’. This more abstract view also brings clarity to the ongoing conversation of whether URIs can be (and should be) universal persistent identifiers.