The program first examines the connect string to determine if all the needed connection information has been provided. For example, for Oracle, all the needed information is on the command line:
Arc: CONNECT oracle user/password@servicename
If the connect string does not contain all the necessary connection information, the program checks the third line of the database definition file. For example, for Oracle, the third line of the file $ARCHOME/database/oracle.dbs looks like this:
ARC/INFO 8.0 - Oracle Server
If neither the connect string, nor the database definition file contain the necessary connection information, the program attempts to retrieve the information from the system environment variables set up for the DBMS. For Oracle, the system environment variables would be the ORACLE_HOME, ORACLE_SID, and TWO_TASK, all of which could be declared in the UNIX .cshrc file.