The field of digital preservation is being defined by a set of standards developed top-down, starting with an abstract reference model (OAIS) and gradually adding more specific detail. Systems claiming conformance to these standards are entering production use. Work is underway to certify that systems conform to requirements derived from OAIS. We complement these requirements derived top-down by presenting an alternate, bottom-up view of the field. The fundamental goal of these systems is to

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... ure that the information they contain remains accessible for the long term. We develop a parallel set of requirements based on observations of how existing systems handle this task, and on an analysis of the threats to achieving the goal. On this basis we suggest disclosures that systems should provide as to how they satisfy their goals.