What is a tiered schema pattern

Layered (layer) mode is one of the most common architectural patterns.

Layering describes an architectural design process that starts with the lowest level of abstraction, called the 1th tier. This is the basis of the system. Step up the abstract ladder by placing the J layer above the J-1 layer until it reaches the highest level of the function, called the nth layer.

Thus, the layered pattern can be defined as: separating the components of the solution into different tiers. The components in each layer should remain cohesive and should be roughly at the same level of abstraction. Each layer should be loosely coupled with the layers underneath it.

The key point of a layered pattern is to determine dependencies: by layering, you can limit the dependencies between subsystems, making the system more loosely coupled and easier to maintain.

The following are the Basic principles for layering a system:

-Visibility. Each subsystem can only be dependent on the subsystems of the same layer and its next layer.

-Variability. Top-level placement of elements that change with the user's needs. The bottom-level placement of elements that change with the implementation platform (Hardware, language, operating system, database, and so on). The intermediate interlayer placement is widely applicable to various systems and elements of the implementation environment. If further partitioning in these large classes helps organize the model, add more layers.

Versatility Abstract model elements are generally placed at the lower level of the model. If they are not specific to the implementation, they tend to place them in the middle tier.

-Number of layers. For small systems, the three layer is sufficient. For complex systems, 5-7 layers are usually required. Regardless of complexity, if more than 10 layers, it needs to be considered carefully. The more layers, the more careful you need to be.

Common layered Schema Patterns:

1. Client-server model (CLIENT-SERVER,C/S).

2. Three layer model: User presentation layer, business logic layer, data layer.

3. The technical composition model of multilayer structure: presentation layer, middle layer and data layer.

4. Network system commonly used three layer structure: core layer, aggregation layer and access layer.

5. Rup Typical layering method: Application layer, professional business layer, middleware layer, system software layer.

6. Java-based B/S mode system structure: browser-side, server-side, request-receiving layer, request processing layer.

7. A six-layer structure: Functional layer (user interface), module layer, assembly layer (software bus), service layer (data processing), database layer, core layer.

What is a tiered schema pattern