Introduction

Syntax as it is defined in information science describes the way in which metadata is encoded in order to assemble its semantic components into structures which mean more than the contents of these basic units alone. We must be able to read metadata and understand how it is structured if we are to use it and share it with others; this requires an understanding of its syntactical underpinnings. The choice of syntax is for this reason the first important decision that must be made in the design of an integrated metadata strategy.

There are a number of criteria that we should apply to our choice of encoding mechanism in order to follow the basic principles outlined earlier. We need metadata to be flexible and malleable enough to be able to support all stages of the digital curation lifecycle (Principle 1). This means that we should be able to manipulate and transform it into a form which allows it to perform its role at each of these stages. This feature is also needed if it is to act as the three types of information package within the OAIS model (Principle 2).

For long-term preservation (Principle 2 again) it should be in a format that is robust for archival purposes. This requires it to be independent of any single software application (Principle 5) for decoding, reading and processing. It should be interoperable as far as possible (Principle 3), and so capable of being transferred between systems with minimal manipulation. It should also be a widely recognised standard in its own right (Principle 7).

The recommendation for metadata syntax here is XML. This ‘language’ has a long history stretching back to the 1960s, when it began life as the Standard Generalised Markup Language (SGML), a mechanism for tagging electronic texts for linguistic analysis. XML is a slightly simplified variant of the now almost entirely superseded SGML which has found a key role as a vehicle for metadata. It is text based in the same way as SGML, is one of the simplest formats available and is decodable by almost any application. Although the way in which XML is encoded is simple, it can encompass metadata of great richness and complexity because it contains sophisticated mechanisms for storing it and building up elaborate structures of semantic interrelationships between its constituent parts.