Web services vs. CORBA and DCOM

Web services
Web services use HTTP protocol for sending and receiving messages between the applications. 
The data encoding in web services is based on XML. 
Web services are defined using WSDL (Web Services Description Language).

• Web services are discovered using UDDI (Universal Description, Discovery and Integration).
• Web services are firewalls friendly.
• Web services supports interoperability i.e. cross platform integration is possible.

CORBA and DCOM

• These technologies use non-standard protocol, i.e. CORBA uses IIOP (Inter Internet Object Protocol), and DCOM uses RPC (Remote Procedure Calls)
• CORBA components are defined using CORBA Interface Description Language; DCOM components are defined using Microsoft Interface definition languages
• CORBA components are discovered using the CORBA registry, DCOM using the Registry.
• DCOM is a proprietary protocol that does not support interoperability and has firewall problems as DCOM transfers data in binary format and it uses many ports to call remote functions.
• CORBA uses the IIOP protocol, which is non-Internet friendly.
• CORBA and DCOM are fine for building enterprise applications that runs on the same platform and not good enough for applications that span platforms and languages.