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These concepts are rendered as a collection of nested folders and generally represent child-parent (or is-a) relationships. Researchers locate these concepts by using a hierarchical tree, or taxonomy. When you use the demo i2b2 site (username "demo", password "demouser" are already filled in), you will see the i2b2 ontology tree on the upper-left side of the user interface. We also refer to that listing as a group of ontologies, where each category or top-level taxonomy is called an ontology in its own right. 

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