As part of SCAPE's work on preservation policies we have been creating a vocabulary that can be used to describe control level policies. As discussed in an earlier blog post
by Catherine Jones
and in , control policies are our third level of policy, with preservation procedure and guidance policies providing higher levels.
Control policies are expressions of states of affairs or desired states of affairs. Ideally these policies can be tested and appropriate action taken depending on the result. For example a control policy may express characteristics of the formats used to represent content in a content set held by an organisation. By expressing these low level policies in a structured, machine readable way, such as through the SCAPE Content Policy Model, we allow the possibility of actioning, testing or validating those policies through some computational process. Through the use of a standardised, common vocabulary for expressing such policies, we can also facilitate sharing of information between components of a preservation ecosystem. This is further explored in .
Key entities described in the vocabulary include notions of Content Set, User Community, Objective — the atomic building blocks of the policies, further discussed below — and Preservation Case, where a case ties a collection of Objectives to a Content Set and User Community.
Objectives are concerned with measures, where a measure is the result of the measurement of an attribute. For example, the attribute compression indicates the compression used for an object, while measures for that attribute might include compression type, compression algorithm or compression algorithm covered by patent (indicating whether licensing fees might apply when using a certain algorithm). An Objective then refers to a particular preservation measure and will give an associated value, qualifer (greater than, less than, equals etc) and a modality describing the desirability of the particular measure-value pair (i.e. MUST, MUST NOT, SHOULD etc).
The policy model uses RDF as its representation language, and the control policy statements are held in a triple store which can then be queried using SPARQL. This use of RDF supports a Linked Data approach — a requirement identified for the control policy representation. he model then allows us to express information about control policies in an unambiguous way which can then me consumed by other components in the SCAPE ecosystem, for example SCOUT or PLATO. The basic framework for the model is defined as an OWL ontology. Measures used in control policy statements are described using spreadsheets, which are then converted to the RDF formats which are used for delivery of the control policies. The intention here is that the general framework for the description of policies is fixed, but additional measures may defined by particular communities.
Further information about the Policy Specification Model can be found in SCAPE Project Deliverable D13.1, available from the project web site .
- Preservation Policy Levels in SCAPE. Barbara Sierman, Catherine Jones, Sean Bechhofer and Gry Elstrøm, iPRES 2013, 10th International Conference on Preservation of Digital Objects.
- Open Preservation Data: Controlled vocabularies and ontologies for preservation ecosystems. Hannes Kulovits, Michael Kraxner, Markus Plangg, Christoph Becker and Sean Bechhofer, iPRES 2013, 10th International Conference on Preservation of Digital Objects.
- SCAPE Project Site http://www.scape-project.eu/