Building meta models with EMF's internal tools is tedious. Using the tree view based editors doesn't scale. Once you're at more than, say, 30 metaclasses, things become hard to work with. The same is true for GMF's Ecore editor. Since you cannot easily factor a large meta model into several diagrams, the diagram get cluttered and layouting becomes almost impossible. One way to solve this problem is to use UML tools to draw the meta model and then transform the UML model into an Ecore instance. The oAW uml2ecore utiliy transforms a suitably structured Eclipse UML2 model (which can be created using various tools) into an ecore file.