Introduction

The previous chapter covered the semantics of descriptive metadata, the meaning of the fields or elements that contain it. Agreeing on a standard for these, such as MODS, is an important step towards creating a coherent metadata strategy for discovery, preservation and interoperability but it fulfils only part of the requirements for achieving these. We must also exercise some control over the content that populates these fields, specifically, what goes into each and the way in which it is formatted. Only by imposing some degree of consistency in both of these can we begin to realise the potential of a collection's descriptive metadata.

Enforcing content rules is one of the basic principles for a metadata strategy outlined in Chapter 3 (Principle 4: ‘Control metadata content wherever possible’). To do so effectively requires us to apply Principle 7 (‘Use standards whenever possible’) in order to root our work in the best practices of a professional community. This will enhance our ability to apply Principle 3 (‘Ensure interoperability’) by making our metadata readily accessible to others in form and content. Controlling content will also ‘Support all stages of the digital curation lifecycle’ (Principle 1) and ‘Support the long-term preservation of the digital object’ (Principle 2) by providing metadata that is consistent and intelligible now and in the future.

Why content rules are needed

The aim of content rules is to ensure a degree of consistency in metadata beyond that provided by the semantics of the standards discussed in the previous chapter. A field in a scheme and its definition as documented can go only so far in clarifying what its content should be. This is particularly true of Simple DC, the semantic scope of whose fields is deliberately broad and, inevitably, imprecise; for instance, knowing that the Title field contains a ‘name given to a resource’ tells us little about what to expect to find there. Even the stricter semantics of MODS leave plenty of room for inconsistency. The <titleInfo> element from Example 7.2 in the previous chapter provides more details than DC Title but does not tell us exactly what its content is.