Service-Oriented Architecture - Guide to Cloud Computing for Business and Technology Managers - page 158

designed and implemented based solely with reference to the pub-
lished service contracts without any need to contact the concerned
developers or without any access to the developers of the service
providers.
c. Simplified maintenance : As services are modular and loosely coupled,
they simplify maintenance and reduce maintenance costs.
d. Incremental adoption : As services are modular and loosely coupled,
they can be developed and deployed in incremental steps.
7.3 Characteristics of SOA
7.3.1 Dynamic, Discoverable, Metadata Driven
Services should be published in a manner by which they can be discovered
and consumed without intervention of the provider. Service contracts should
use metadata to define service capabilities and constraints and should be
machine readable so that they can be registered and discovered dynamically
to lower the cost of locating and using services, reduce corresponding errors,
and improve management of services.
7.3.2 Designed for Multiple Invocation Styles
Design and implement service operations that implement business logic
that supports multiple invocation styles, including asynchronous queuing,
request/response, request/callback, request/polling, batch processing, and
event-driven publish/subscribe.
7.3.3 Loosely Coupled
This implies loose coupling of interface and technology; interface coupling
implies that the interface should encapsulate all implementation details and
make them nontransparent to service requesters, while technology coupling
measures the extent to which a service depends on a particular technology,
product, or development platform (operating systems, application servers,
packaged applications, and middleware).
7.3.4 Well-Defined Service Contracts
Service contracts are more important than the service implementations
because it defines the service capabilities and how to invoke the service in
an interoperable manner. A service contract clearly separates the service's
externally accessible interface from the service's technical implementation;