The difference between tier vs layer application

See Pet Shop as an example of 3 layer architecture. I'll implement both BLL and DAL as service object, which on its own does not hold any states. Since they are stateless, I can use singleton pattern and let a factory hold on to it for easy reference.

Here are some example CRUD methods you could have:

FooInfo DALFactory.FooService.Retrieve(int id);
FooInfo BLLFactory.FooService.Retrieve(int id);

IList<FooInfo> DALFactory.FooService.RetrieveAll;
IList<FooInfo> BLLFactory.FooService.RetrieveAll;

FooInfo DALFactory.FooService.Create(FooInfo entity);
FooInfo BLLFactory.FooService.Create(FooInfo entity);

FooInfo DALFactory.FooService.Edit(FooInfo entity);
FooInfo BLLFactory.FooService.Edit(FooInfo entity);

void DALFactory.FooService.Delete(FooInfo entity);
void BLLFactory.FooService.Delete(FooInfo entity);

As you can see in both cases, you pass the same entity object (aka data transfer object) that has no logic whatsoever. This architecture allows you to disconnect UI layer from BLL down the line to rich client and web services combo.

The intension of the Retrieve and RetrieveAll method is to grab the data from the database and stuff it into entity object. Create method adds a new row to the database based on the given entity. In this architecture, there is no "business object" besides Business Logic Layer's BLLFactory.FooService and the entity FooInfo object.

In terms of the lifetime of these objects, the stateless BLLFactory.FooService is created once, and will be reused as long as the app is alive. FooInfo could be created once per object, and then persisted into the ASP.NET session or something.

Here's a quick, dirty, and very general explanation of a 4-tier architecture, which I'm assuming may best apply to your application:

Presentation Layer : The interface to the outside world (web site)
Application Layer : The mechanics necessary to create the interface(s) to the outside world (web application frameworks, web services)
Business Logic Layer : The actual logic that embodies/simulates/emulates your business's processes and workflows (algorithms, transformations, approval processes, etc.)
Database Layer : The database and the logic needed to query information from it

In general, web services are not part of the business logic layer. That layer is usually protected as much as the database layer, because there could be trade secrets or confidential ways of doing things in there, and you usually don't want anyone accessing that directly, except programatically or through approved interfaces (such as web services).

Web services, application layers, and business logic can be aptly compared to Coca-Cola and it's business. Bottles and cans are usually how Joe Blow consumes Coke's product (e.g. web site in the presentation layer), but other businesses want to be able to serve Coca-Cola to their customers as well, so Coke lets them use carbonated water and Coca-Cola syrup (e.g. web services in the application layer). Coke's secret formula (e.g. business logic layer), and Coke's distribution processes to get it into the store (e.g. application layer) are all hidden from the consumer. Joe Blow doesn't care how it gets into the store, he just knows he can get Coke from a variety of sources (web site, mobile client, etc.). And Coke doesn't want people knowing its secret formula (business logic). If you want a Coke, you have to go through a store or a restaurant (approved interfaces).