Use for questions related to the ArcGIS Diagrammer which can be used to create, edit and analyze geodatabase schema
From the home page of ArcGIS Diagrammer for 10.2
ArcGIS Diagrammer is a productivity tool for GIS professionals to create, edit or analyze geodatabase schema. Schema is presented as editable graphics in an environment familiar to users of Microsoft Visual Studio. Essentially ArcGIS Diagrammer is a visual editor for ESRI’s xml workspace documents that can be created in ArcMap or ArcCatalog.