This is an external bridge ontology that contains OWL disjointness constraints.
http://wiki.geneontology.org/index.php/Disjoint_Documentation
Cell differentiation consists of two separate parts: commitment of cell to its fate and the subsequent development of the cell
cellular_component
GO:0005576
extracellular region
Cell differentiation consists of two separate parts: commitment of cell to its fate and the subsequent development of the cell