Schema {
    public static CDDef readDefinition(String fileName) throws Exception
    {{
	return readDefinition(fileName, null);
    }}

    public static CDDef readDefinition(String fileName,
				       CDDef def) throws Exception
    {{
	Schema schema;

	// Open the specified schema-definition file and parse its contents to
	// create the schema object.  But before parsing it, pre-process it to
	// remove comments, etc. and make changes necessary for the parser.
	try {
	    BufferedReader reader =
		new BufferedReader(new FileReader(fileName));
	    schema = parse(Preprocessor.preProcessSchemaDefinition(reader));
	}
	catch (FileNotFoundException e) {
	    throw new Exception("Schema definition file '" + fileName + "'" +
				" not accessible");
	}
	catch (IOException e) {
	    throw new Exception("Error in reading schema definition file '" +
				fileName + "'");
	}
/*
schema.print();
System.out.println();
*/


	// Create an empty CDDef object if none already exists
	if (def == null)
	    def = CDDef.parse(" ( ) ( )");

	// Traverse the schema object to extract the element, attribute and
	// type definitions
	SchemaVisitor sv = new SchemaVisitor(def);
	schema.processDefinition(sv);

	String errors = sv.getErrors();
	if (!errors.equals(""))
	    throw new Exception(errors);

	String namespacePrefixes[] = sv.getNamespacePrefix();
/*
def.print();
System.out.println();
*/

	return def;
    }}


    traversal processDefinition(SchemaVisitor) {
	bypassing -> *,tail,* to *;
    }

    // use for debugging
    public void print() bypassing -> *,tail,* to * (DisplayVisitor);
}