# GO Tutorial: Build Your Own Ontology III

## Exercise III

### Build Your Own Component Ontology

ontology flat file

Load the file into DAG-Edit. It shows part of the GO component ontology but the relationships and some of the definitions have been removed. Your task (should you choose to accept it) is to restore the ontology to its former glory with the appropriate definitions and relationships.

You can use the definitions you came up with earlier for the undefined terms or formulate some afresh. Do the definitions you use affect the relationships you choose between the terms?

Are there any cases where adding species-specific "sensu" terms would allow you to use a more specific parent term? For example, GO has several "thylakoid" terms: "thylakoid (sensu Viridiplantae)" is a part of "chloroplast", "thylakoid (sensu Cyanobacteria)" is a part of "plasma membrane", and "thylakoid (sensu Glaucocystophyceae)" is part of "cyanelle" (a type of plastid). Are there any component terms you could split up in a similar manner?

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