1. What is hierarchical architecture
The system is divided vertically into several layers, with each layer having independent functions and multiple layers cooperating to provide complete functions
Common layered models
| The name of the | Implementation details | The picture |
|---|---|---|
| MVC | Model View Controller |  |
| web+service+dao | Presentation layer: display user instructions Logical layer: The concrete implementation of complex business Data access layer: Handles interactions with storage |
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Examples of layering
| The name of the | Implementation details | The picture |
|---|---|---|
| OSI 7-layer network model TCP/IP 4-layer protocol | Network layer: responsible for end-to-end addressing and establishing connections Transport layer: End-to-end data transfer Two adjacent layers have data interaction isolation concerns, with different layers focusing on different things |
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| Linux file system | VFS: a virtual file system that hides differences between systems A hierarchy is an abstraction of the different implementations at a lower level |
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2. Advantages and disadvantages of stratification
| Advantages of layering | Disadvantages of stratification |
|---|---|
| Layering simplifies system design, with different people focusing on one level Technology market: API, Mid-platform, infrastructure |
Increase the complexity of your code Simple queries that require data transfer between each level |
| Layering can be highly reusable Central, Biz – Lib, BIZ -common |
Each layer is deployed separately to increase network interaction |
| Layering makes it easy to scale horizontally Extend for bottlenecks at one level |
CPU usage (adding machines), slow disk read/write (SSD)…. |
3. How to layer
The boundaries of stratification need to be considered clearly
Due to changes in requirements and business complexity, layering becomes blurred
Open interface layer: encapsulates Service layer methods as open interfaces, and implements gateway security control and flow control.
Web layer: it mainly forwards access control, verifies all kinds of basic parameters, or simply deals with services that do not reuse.
Service layer: business logic layer.
Manager layer: Common business processing layer. This layer has two main functions. First, you can sink some of the common capabilities of the original Service layer into this layer, such as the interaction strategy with cache and storage, middleware access. Second, you can also encapsulate calls to third-party interfaces in this layer, such as payment services, auditing services, etc
DAO layer: Data access layer, which interacts with MySQL, Oracle, and HBase at the bottom.
External interface or third party platform: including RPC open interface of other departments, base platform, HTTP interface of other companies
The Manager layer provides the atomic Service interfaces (the results of multiple calls are consistent), and the Service layer is responsible for orchestrating the atomic interfaces according to the business logic.
4. To summarize
Layered architecture is the external embodiment of software design thought and is a way of implementation.
Single principle: Each layer has a single responsibility
Demeter’s law: data interaction cannot be carried out across layers, but must be carried out between adjacent layers
Open and close principle: the abstraction layer is separated from the implementation layer. The abstraction layer is the summary of the common characteristics of the implementation layer (not modifiable), and the concrete implementation is infinite expansion (optional replacement).
When the complexity of a layer becomes too high, it is split into multiple layers