In order for TopBraid Composer to see an ontology, it must be located in one of the workspace folders. Navigate to the appropriate folder in the Project Explorer, then double-click on the file to open it.
You can copy and paste a file in to the folder using you file management system, such as Windows Explorer. If this operation is performed after Composer has been started, make sure to refresh the files displayed in the Project Explorer. This is done by right-clicking inside the Project Explorer and selecting Refresh.
If an ontology imports another ontology, Composer would try to locate a local copy of the ontology's namespace. If a local file is found, it will always load from the file, so that users do not need to have an internet connection. If the workspace contains multiple copies of the same namespace, for example multiple versions of a file, then the import will be resolved against the most recent file (using the file's time stamp).
Important Note: You cannot have the same base URI open more than once. If you have 2 files which share the same URI, you will need to close one of them before opening the other. Composer associates a base URI with the name of the file. When you open another file with the same base URI as a previously opened file, Composer will display a message advising you that it will now associate the file you are opening with the URI. Press Yes to proceed.
In order to open an RDF file that lies outside of your workspace, you can use File > Open... and select the file. However, this procedure is not recommended because external files are invisible to the imports resolution mechanism and will most likely lead to unexpected results. The preferred way is to use the Project Explorer and workspace. If you do not want (or cannot) copy all your files under the Eclipse workspace root, you can create placeholder/proxy folders that point from your workspace to external folders. The file open wizard will actually ask you to create such a project automatically and then open the file from that imported project. Alternatively, create a link project manually (see the Workspaces page for details).