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Service-Orientation with .NET : Service Façade

5/17/2011 4:29:21 PM
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When pursuing logic-to-contract coupling, additional coupling flexibility can be built into the service architecture by further establishing layers of implementation logic. Service Façade advocates the positioning of façade components between the service contract and the core service logic (Figure 1), as well as between the core service logic and the underlying service implementation resources (in particular legacy resources).
Figure 1. A service façade component used to establish an internal layer of abstraction.


The former positioning protects the core service logic from changes to the contract or impacts that may result from the application of Concurrent Contracts.

The latter positioning of the façade logic allows for core business logic to be captured in one layer and logic proprietary to specific parts of the implementation (such as databases or legacy APIs) to reside in a different layer. When those underlying legacy resources need to be changed or replaced in the future, the impact to the service architecture is further shielded.

Typically a Service Façade  can contain code that:

  • chooses which methods or functions to call in the core implementation

  • compensates for changes in logic and/or data model so that logic-to-contract coupling is retained

  • allows the core business logic to remain physically separate and stable if the service contract itself should need to change

The following series of examples shows how you could build a façade that removes address information from a person.

Consider first the service interface:

Example 1.
[ServiceContract]
interface IPersonService
{
[OperationContract]
person GetPerson(int personId);
}

The following class implements the interface and returns the information that another .NET class produces:

Example 2.
class PersonService : IPersonService
{
public person GetPerson(int personId)
{
return ServiceImplementation.GetPersonById(personId);
}
}

Another class can also implement the interface, but notice that this class doesn’t just return the information that ServiceImplementation creates:

Example 3.
class SimplePersonService : IPersonService
{
public person GetPerson(int personId)
{
var person = ServiceImplementation.
GetPersonById(personId);
person.address = null;
return person;
}
}

The class that really implements most of the underlying façade functionality is ServiceImplementation, as follows:

Example 4.
class ServiceImplementation
{
public static person GetPersonById(int personId)
{
return new person { id = personId };
}
}

Note how in the preceding example, the two different façade components implement WCF code (since they implement the interface that is annotated with WCF attributes), but the core service logic is not WCF code. This allows the core implementation to exist unaware of WCF.

Other -----------------
- Service-Orientation with .NET : Decoupled Contract
- Service-Orientation with .NET : Service Loose Coupling
- Service-Orientation with .NET : Service Contracts and Interoperability - Canonical Protocol
- Service-Orientation with .NET : Service Contracts and Interoperability - Data Model Transformation
- Service-Orientation with .NET : Service Contracts and Interoperability - Canonical Schema
- Service-Orientation with .NET : Standardized Service Contract
- Cloud Services with Windows Azure : Windows Azure Storage
- A REST Service in Windows Azure
- Cloud Services with Windows Azure : A Web Service in Windows Azure
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