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soa学习第二篇

(2006-04-29 23:33:22)
分类: 吴定明

Pattern 4: Virtual provider

Context and problems: ecosystem develops gradually -- not all services you require are available as Web services or through a service specification, yet. You need to develop the critical mass of services that enable your line of business, enterprise, or ecosystem.

Solution: Create a virtual provider by specifying the service you need and assuming it is being provided. Create the provider yourself by using a proxy to communicate with the legacy system, while using an adaptor to transform the protocol used to one you want/need/have specified in your service description/contract. You encapsulate the proxy and adaptor in a façade because the number of adaptors may increase at random based on new systems and protocols that have to be transformed in the future. Therefore, use a façade to encapsulate the set of adaptors that will allow communication with existing API?s.

Related patterns: The latter is referred to as an Enterprise Service Bus, if rule objects for mediation, routing, transformation, and policies are added to the virtual provider.

Virtual provider includes a façade, a proxy, and one or more adaptors for target system connection types. It becomes a service bus once you add rule objects for routing and policy management within the virtual provider.

 

Pattern 5: Service integrator

Context and problems: integrating with redundant back-end functionality, locked-in legacy systems (custom and packaged applications) remains a challenge. You want to have a single point of access to your back-end functionality in order to be able to recompose the individual pieces of that functionality in new combinations along with the need to monitor and manage those new services.

The service integrator is responsible for managing multiple integration layers. Within a service-computing ecosystem, the service integrator allows a single point of integration, monitoring, and managing for the ecosystem. This ecosystem is fractal in nature: this organization in its architecture can be found at various scopes. It starts within an organization at a project level, goes up to a business line, and covers its various existing applications across lines of business into the enterprise architecture. This allows the integration of two or more enterprise architectures for collaboration within the ecosystem.

Solution: Therefore, introduce a specific layer of integration into the architecture for the integration of services and manage that layer through a service integrator. The service integrator provides a single point of access for otherwise redundant services.

To facilitate this, externalize the variations into remote service strategies, within the context of a virtual provider at the implementation end. In this way, start to build the foundation for a graceful transition from a tightly coupled brittle architecture to a more loosely-coupled, dynamically reconfigurable architecture.

 

Pattern 5: ESB (Enterprise Service Bus)

Context and problems: The patterns described in this paper have illustrated some commonly used techniques to deliver in reality some elements of the flexibility promised by SOA in a realistic and incrementally realizable manner. However, as an organization progressively adopts service orientation across applications, legacy systems, channel technologies, and more, the middlware required to support services and the management of services and technologies used to support them become complex issues. An important part of the solution to managing this complexity is the provision of a common infrastructure for service communication, mediation, transformation, and integration. This infrastructure can also act as a point of control to apply service management, security, monitoring, and instrumentation to the Service-Oriented Architecture. Such a common infrastructure is described by the Enterprise Service Bus.

Solution: Create an Enterprise Service Bus to provide the middleware capabilities throughout the organization to support service interactions. The ESB should support the communication, mediation, transformation, and integration technologies required by those services and should be capable of a distributed geographical deployment, but with a common model for management and administration. the key features of an ESB, which include:

  • It is deployed as one or more "hub" components. Each hub provides a localized but resilient capability to perform routing, transformation, security, and other functions commonly referred to as "intermediary" functions.
  • It has a namespace directory and administration services used to administer the services it supports access to. In a geographically deployed ESB, the administration services maintain a consistent configuration across a network of cooperating Hubs.
  • It has a number of inbound ports. Each inbound port is configured to receive service requests on a set of addresses using a particular protocol, for example, SOAP/HTTP or WebSphere MQ.
  • It has a number of outbound ports. Each outbound port is configured to forward service requests to and receive responses from a set of addresses using a particular protocol.

This configuration allows the ESB to support the virtual service provider pattern and remote rervice strategy for any number of services across an enterprise in a common way. In addition, the ESB can provide transformations between a variety of security, data format, or transactional models between service requesters and providers. In this way, the ESB acts as a control and encapsulation point for the inevitable complexity and heterogeneity encountered in an enterprise context.

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