SOA versus Distributed Architecture:

Application logic:

Distributed applications place all their application logic on the server side. Here the emphasis is given on,

1. how application logic is partitioned.
2. where the partitioned units of processing logic should reside.
3. how the units of processing logic should interact.

In distributed applications components are designed with different degrees of functionality and to what extent they are considered reusable by other tasks. Components residing on same server communicates API’s. In SOA web services establishes a loosely coupled environment, allowing individual services to participate.

Another difference is in how services exchange information.  Traditional components provides the methods which send and receive parameter data. Web services communicate with SOAP messages which rely on document-style messages.

Distributed internet architecture use proprietary communication protocols like DCOM and CORBA for data exchange where as SOA relies on message-based communication.

Security:

To ensure safe transportation of information and to identify user credentials encryption is assed to HTTP protocol. SOA emphasizes on placement of security logic onto messaging level. SOAP messages provide header blocks where security logic can be placed.