64

Key Web Services Design Decisions

  What kinds of exceptions will the service throw back to the clients, and when 

will this happen?

  How are you going to let clients know about your Web service? Are you going 

to publish your service in public registries, in private registries, or some way 

other than registries?

Before exploring the details of these design issues, let's look at a service from

a high level. Essentially, a service implementation can be seen as having two

layers: an interaction and a processing layer. (See Figure 3.2.) 

E

It is helpful to view a service in terms of layers: an interaction layer and a pro 

cessing layer.

The service interaction layer consists of the endpoint interface that the service

exposes to clients and through which it receives client requests. The interaction

layer also includes the logic for how the service delegates the requests to business

logic and formulates responses. When it receives requests from clients, the inter 

action layer performs any required preprocessing before delegating requests to the

business logic. When the business logic processing completes, the interaction

layer sends back the response to the client. The interaction layer may have addi 

tional responsibilities for those scenarios where the service expects to receive

XML documents from clients but the business logic deals with objects. In these

cases, you map the XML documents to equivalent object representations in the

interaction layer before delegating the request to the business logic.

The service processing layer holds all business logic used to process client

requests. It is also responsible for integrating with EISs and other Web services. In

the case of existing applications adding a Web service interface, the existing appli 

cation itself typically forms the service processing layer.

Service Implementation

Service

Service

Service Client

Interaction

Processing

Layer

Layer

Figure 3.2

Layered View of a Web Service