An ontology is a formal representation of a set of concepts within a domain and the relationships between those concepts. Ontologies are the main kind of resource used for the Semantic Web or knowledge management as a knowledge representation. The concepts are linked together by hierarchical relationships in one hand and semantic relationships in another hand (See: Athenawiki - Definitions).
Explore further the Linked Heritage learning object: Terminology.
Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH)
The Open Archives Initiative Protocol for Metadata Harvesting, commonly referred to as OAI-PMH or OAI protocol, is a protocol defined by the Open Archive Initiative. It provides a method for data providers to make records for their items (as a means of exposing metadata) available for harvesting by service providers that operate through a harvester.
Explore further the Linked Heritage learning object: MINT Services.