ociplogon() creates a persistent connection to an Oracle 8 database and logs on. The optional third parameter can either contain the name of the local Oracle instance or the name of the entry in tnsnames.ora to which you want to connect. If the optional third parameter is not specified, PHP uses the environment variables ORACLE_SID (Oracle instance) or TWO_TASK (tnsnames.ora) to determine which database to connect to.
See also ocilogon() and ocinlogon().