Pros and Cons of combining the business layer and the Data Layer in one WCF service

Question

I have an application that uses the 3 layer 2 tier business model, namely Presentation, Business and Data Layers with Application and Service Tiers. We have already decided to use a WCF service on its own tier for all the Data Layer requests (CRUD). The question I have now is whether or not to combine the Business Layer with the Data Layer in the WCF Service, and then the UI makes calls to the service which handles ALL Business and Data Operations.

I am opposed to this idea, as the service in my opinion should be a dumb service, which only handles CRUD operations. The Business layer should be on the application side, but encapsulated in its own layer, also being the only layer to access the Data Layer.

I might be being plain silly, but I would like to have the internet's say on the matter, as well as any pros and cons if possible.

All responses are appreciated!

Answer 1

If there is any chance that another presentation layer, such as a website, will need access to the business and data layers, then it makes sense to create the following layers on the service side:

1. Service endpoint: a simple data pass-through that is responsible for translating incoming requests, in the technology of your choice, into requests the business layer understands.
2. Business layer: your domain objects and business services with rules required to run your business. This layer makes calls into your data layer and knows nothing about the service endpoint.
3. Data layer: a simple translation of business domain objects into the required objects of whatever you are interacting with; whether that is a database or a third-party service endpoint.

Now you have a nice, maintainable, and deployable microservice that is specific to a particular domain in your problem space.

Check out Martin Fowler's article on microservices for further details on the subject.