Summary

This chapter has discussed the three components that compose a Web services model: presentation, interface, and security. If you carefully identify your objectives in each of these areas, you will be much more successful in your design and deployment of Web services as a provider. Even as a consumer of Web services, you will have a better idea of what to look for in a Web service as well as how to successfully implement Web services in your applications.

The key issues in defining your presentation model are the level of exposure for your Web services and the level of valued-added services you want to provide. The level of exposure may range from masked to isolated or be truly embedded inside your consumer's application(s). The services you provide in the presentation layer might include interface content, style information, or data validation. A combination of these three is usually suitable for any Web services interacting with end users.

Taking either the level of exposure or the level of service to extremes adds to your design and development efforts considerably and may not benefit you if the need doesn't exist. However, if there is a demand for multiple models, it is better to provide them independently so that you do not weigh down the consumers with minimal expectations with extraneous data.

The interface model is defined by the complexity of the processes you expose through your Web services and the amount of efficiency you want to have in the consumer-to-provider communication. A Web service may expose a simple one-call function or an involved workflow. In the case of a workflow, it is important to identify the processes and mechanisms through which you will manage state.

The payload efficiency is determined by the amount of overhead calls involved in the entire process of the Web service. Each step can be treated independently, or steps can lead into one another with inline error handling. Keep in mind that, for every efficiency gained in the process itself, extra effort may be needed by the provider and/or the consumers that implement it.

The main areas of the security model are system access, application authentication, transport integrity, and payload validation. Designing an appropriate solution to handle all four for a given environment should lay a good foundation for many Web services.

System access is the first step to allowing consumers to reference your Web services, and so it is also the first barrier to keeping unwanted users out. Once into the system, the application authentication process determines what users can do in the application. Of course, you want to make sure that you secure the consumer-to-provider communication when necessary, and your transport integrity solution should address that. Finally, you want to be able to trust the data itself as it comes into your Web services listener. Executing processes against invalid data can be potentially damaging, so you need to rely on your payload validation process.

Once you have laid all this out, you are ready to start designing your Web services. Fortunately, your model goes a long way to defining your design, and filling in the gaps will be much easier with the narrowed focus your model provides. You will then be ready to take the next step of developing and deploying Web services.