Using SOAP Connections
SOAP is the protocol that underlies the built-in support for Web Service applications. SOAP marshals method calls using an XML encoding. SOAP connections use HTTP as a transport protocol.
SOAP connections have the advantage that they work in cross-platform applications because they are supported on both the Windows and Linux platforms. However, your best choice for multi-tiered applications is DataSnap, which also supports all the platforms supported by RAD Studio. DataSnap also offers mobile connectors and potentially full mobile app development.
Because SOAP connections use HTTP, they have the same advantages as Web connections: HTTP provides a lowest common denominator that you know is available on all clients, and clients can communicate with an application server that is protected by a "firewall." For more information about using SOAP to distribute applications, see Using Web Services..
As with HTTP connections, you cannot use callbacks when the connection is formed via SOAP.