The prov family of documents are the final output of the World Wide Web Consortium Provenance Working Group, chartered to specify a representation of provenance to facilitate its exchange over the Web. This article reflects upon the key requirements, guiding principles, and design decisions that influenced the prov family of documents. A broad range of requirements were found, relating to the key concepts necessary for describing provenance, such as resources, activities, agents and events, and

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... to balancing prov's ease of use with the facility to check its validity. By this retrospective requirement analysis, the article aims to provide some insights into how prov turned out as it did and why. Benefits of this insight include better inter-operability, a roadmap for alternate investigations and improvements, and solid foundations for future standardization activities. Requirement OD2 (Inverse Relation). The prov ontology is to define all, but encourage use of certain, property inverses.