You can connect a custom SharePoint list (no Web part) directly with external data from Oracle database tables or views using the
SharePoint Business Data List Connector (BDLC).

You can set the connection string, the select statement and the primary keys (if any) in the SharePoint list settings dialog. Here are some sample connection strings for Oracle databases.
To open a connection to Oracle database with standard security use this one:
"Provider=MSDAORA; Data Source=Your_Oracle_Database; UserId=Your_Username; Password=Your_Password;"
Or
"Provider= OraOLEDB.Oracle; Your_Oracle_Database; UserId=Your_Username; Password=Your_Password;"
To open a trusted connection to Oracle database please use this connsction string:
"Provider= OraOLEDB.Oracle; DataSource=Your_Oracle_Database; OSAuthent=1;"
If using trusted connections, please make sure, that your SharePoint users and (in case of automatic updates) the timer process account has proper access to the database.
You can use select statements and primary key(s) as usual with Oracle.
If primary keys are available, you can use list alerts and workflows to start business actions in SharePoint, if external Oracle data is changed.