Difference between SID and SERVICE_ID in tnsnames.ora

I'm seeking for a technically exact explanation about the difference between SID and SERVICE_ID in the TNSNAMES.ORA alias assignment.

And, moreover, at which one can the domain extension be used and when?

Example:

EXAMPLE=

(DESCRIPTION =

    (ADDRESS_LIST =

      (ADDRESS = (PROTOCOL = TCP)(HOST = oracleserver) (PORT = 1521))

    )

    (CONNECT_DATA =

      (SERVICE_NAME = ORCL )

    )

  )

vs.

EXAMPLE=

(DESCRIPTION =

    (ADDRESS_LIST =

      (ADDRESS = (PROTOCOL = TCP)(HOST = oracleserver) (PORT = 1521))

    )

    (CONNECT_DATA =

      (SID = ORCL )

    )

  )

Sometimes I see (SERVER = DEDICATED) also in CONNECT_DATA. In opposite to what does that stand?

I already learnt that, if the GLOBAL DATABASE NAME  (GLOBAL_NAME) is set on the server, one has to use