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Services are stateless
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Services should minimize the amount of state information they manage and the duration for which they hold it. State information is data specific to a current activity. While a service is processing a message, for example, it is temporarily stateful. If a service is responsible for retaining state for longer periods of time, its ability to remain available to other requestors will be impeded.
Statelessness is a preferred condition for services and one that promotes reusability and scalability. In order for a service to retain as little state as possible, its individual operations need to be designed with stateless processing considerations.
 Stateless and stateful stages a service passes through while processing a message.
A primary quality of SOA that supports statelessness is the use of document-style messages. The more intelligence added to a message, the more independent and self-sufficient it remains.
This page contains excerpts from:
Service-Oriented Architecture:
Concepts, Technology, and Design
by Thomas Erl
(ISBN: 0131858580, Prentice Hall/PearsonPTR, Hardcover, 792 pages).
For more information, visit www.soabooks.com.
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