1. Standardized Service Contract
Services adhere to a service-description. The Standardized Service Contract design principle essentially requires that specific considerations be taken into account when designing a service's public technical interface and assessing the nature and quantity of content that will be published as part of a service's official contract.
2. Loose Coupling
Services minimize dependencies on each other. Coupling refers to a connection or relationship between two things. This principle advocates the creation of a specific type of relationship within and outside of service boundaries, with a constant emphasis on reducing ("loosening") dependencies between the service contract, its implementation, and its service consumers. The principle of Service Loose Coupling promotes the independent design and evolution of a service's logic and implementation while still guaranteeing baseline interoperability with consumers that have come to rely on the service's capabilities.
3. Service Abstraction
Services hide the logic they encapsulate from the outside world. Abstraction ties into many aspects of service-orientation. On a fundamental level, this principle emphasizes the need to hide as much of the underlying details of a service as possible. Doing so directly enables and preserves the previously described loosely coupled relationship. Service Abstraction also plays a significant role in the positioning and design of service compositions.Various forms of meta data come into the picture when assessing appropriate abstraction levels. The extent of abstraction applied can affect service contract granularity and can further influence the ultimate cost and effort of governing the service.
4. Service Reusability
Logic is divided into services with the intent of maximizing reuse. Reuse is strongly emphasized within service-orientation; so much so, that it becomes a core part of typical service analysis and design processes, and also forms the basis for key service models. The advent of mature, non-proprietary service technology has provided the opportunity to maximize the reuse potential of multi-purpose logic on an unprecedented level.
The principle of Service Reusability emphasizes the positioning of services as enterprise resources with agnostic functional contexts. Numerous design considerations are raised to ensure that individual service capabilities are appropriately defined in relation to an agnostic service context, and to guarantee that they can facilitate the necessary reuse requirements.
5. Service Autonomy
Services should have control over the logic they encapsulate. For services to carry out their capabilities consistently and reliably, their underlying solution logic needs to have a significant degree of control over its environment and resources. The principle of Service Autonomy supports the extent to which other design principles can be effectively realized in real world production environments by fostering design characteristics that increase a service's reliability and behavioral predictability.
This principle raises various issues that pertain to the design of service logic as well as the service's actual implementation environment. Isolation levels and service normalization considerations are taken into account to achieve a suitable measure of autonomy, especially for reusable services that are frequently shared.
6. Service Statelessness
Ideally, services should be stateless. The management of excessive state information can compromise the availability of a service and undermine its scalability potential. Services are therefore ideally designed to remain stateful only when required. Applying the principle of Service Statelessness requires that measures of realistically attainable statelessness be assessed, based on the adequacy of the surrounding technology architecture to provide state management delegation and deferral options.
7. Service Discoverability
Services can be discovered (usually in a service registry). For services to be positioned as IT assets with repeatable ROI, they need to be easily identified and understood when opportunities for reuse present themselves. The service design therefore needs to take the "communications quality" of the service and its individual capabilities into account, regardless of whether a discovery mechanism (such as a service registry) is an immediate part of the environment.
8. Service Composability
Services decomposition break big problems into little problems.As the sophistication of service-oriented solutions continues to grow, so does the complexity of underlying service composition configurations. The ability to effectively compose services is a critical requirement for achieving some of the most fundamental goals of service-oriented computing.
Complex service compositions place demands on service design that need to be anticipated to avoid massive retro-fitting efforts. Services are expected to be capable of participating as effective composition members, regardless of whether they need to be immediately enlisted in a composition. The principle of Service Composability addresses this requirement by ensuring that a variety of considerations are taken into account.
9. Service Interoperability
Services should use standards that allow diverse subscribers to use the service. Interoperability is considered so obvious these days that it is often dropped as a principle. A fundamental goal of applying service-orientation is for interoperability to become a natural by-product, ideally to the extent that a level of intrinsic interoperability is established as a common and expected service design characteristic.
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