Web Application Architectures
We have already seen that modern web applications involve a significant amount of complexity, particularly on the server side.
A typical web application involves numerous protocols, programming languages and technologies spread throughout the web stack.
Developing, maintaining and extending a complex web application is extremely difficult – but, building it using a foundation of solid design principles can simplify each of these tasks.
Software engineers use abstraction to deal with this type of complexity. Design patterns provide useful design abstractions for object-oriented
systems.
Design Patterns
Definition (Design Pattern)
A design pattern is a description of interacting objects and classes that interact to solve a general design problem within a particular context.
A design pattern is an abstract template that can be applied over and over again.
The idea is apply abstract design patterns in order to solve specific design problems that occur while building real systems.
Design patterns provide a way to communicate the parts of a design, i.e., it’s the vernacular software engineers use to talk about designs.
Client-Sever Model
The n-tier architecture is a highly useful design pattern that maps to the client-server model.
This design pattern is based on the concept of breaking a system into different pieces or tiers that can be physically separated:
– Each tier is responsible for providing a specific functionality.
– A tier only interacts with the tiers adjacent to it through a well-defined
interface.
Ex.
Print server – 2-tier architectural pattern.
Early web applications – 2-tier client-server architecture:
- User interface (browser) functionality resided on the (thin) client.
- Server provided static web pages (HTML).
- Interface between the two via the hypertext transfer protocol (HTTP).
n-Tier Architecture
Additional tiers show up when the application functionality is further partitioned.
What are the advantages of such a design?
The abstraction provides a means for managing the complexity of the design.
Tiers can be upgraded or replaced independently as requirements or technology change — the new tier just needs to use the same interfaces as the old one.
It provides a balance between innovation and standardization.
Tiered systems are much easier to build, maintain, scale and upgrade.
3-Tier Architecture
One of the most common is the 3-tier architecture:
- Presentation tier – The user interface.
- Application (logic) tier – Retrieves, modifies and/or deletes data in the
data tier, and sends the results to the presentation tier. Also
responsible for processing the data itself.
- Data tier – The source of the data associated with the application.
A modern web application is often deployed over the Internet as a 3-tier architecture:
- Presentation tier – User’s web browser.
- Application (logic) tier – The web server and logic associated with
generating dynamic web content, e.g., collecting and formatting the
results of a search.
- Data tier – A database.
6-Tier Web Application Architecture
The Application tier is often subdivided into two tiers:
- Business logic tier – Models the business objects associated with the application, e.g., accounts, inventories, etc., and captures the business rules and workflows associated with how these processes can be processed and manipulated.
- Data access tier – Responsible for accessing data, and passing it to the business logic tier, e.g., account balances, transactions, etc.
The Presentation tier is often subdivided into two tiers:
- Client tier – client-side user interface components.
- Presentation logic tier – server-side scripts for generating web pages.
Finally, the web server is often separated out into its own Web tier.
We have already seen that modern web applications involve a significant amount of complexity, particularly on the server side.
A typical web application involves numerous protocols, programming languages and technologies spread throughout the web stack.
Developing, maintaining and extending a complex web application is extremely difficult – but, building it using a foundation of solid design principles can simplify each of these tasks.
Software engineers use abstraction to deal with this type of complexity. Design patterns provide useful design abstractions for object-oriented
systems.
Design Patterns
Definition (Design Pattern)
A design pattern is a description of interacting objects and classes that interact to solve a general design problem within a particular context.
A design pattern is an abstract template that can be applied over and over again.
The idea is apply abstract design patterns in order to solve specific design problems that occur while building real systems.
Design patterns provide a way to communicate the parts of a design, i.e., it’s the vernacular software engineers use to talk about designs.
Client-Sever Model
The n-tier architecture is a highly useful design pattern that maps to the client-server model.
This design pattern is based on the concept of breaking a system into different pieces or tiers that can be physically separated:
– Each tier is responsible for providing a specific functionality.
– A tier only interacts with the tiers adjacent to it through a well-defined
interface.
Ex.
Print server – 2-tier architectural pattern.
Early web applications – 2-tier client-server architecture:
- User interface (browser) functionality resided on the (thin) client.
- Server provided static web pages (HTML).
- Interface between the two via the hypertext transfer protocol (HTTP).
n-Tier Architecture
Additional tiers show up when the application functionality is further partitioned.
What are the advantages of such a design?
The abstraction provides a means for managing the complexity of the design.
Tiers can be upgraded or replaced independently as requirements or technology change — the new tier just needs to use the same interfaces as the old one.
It provides a balance between innovation and standardization.
Tiered systems are much easier to build, maintain, scale and upgrade.
3-Tier Architecture
One of the most common is the 3-tier architecture:
- Presentation tier – The user interface.
- Application (logic) tier – Retrieves, modifies and/or deletes data in the
data tier, and sends the results to the presentation tier. Also
responsible for processing the data itself.
- Data tier – The source of the data associated with the application.
A modern web application is often deployed over the Internet as a 3-tier architecture:
- Presentation tier – User’s web browser.
- Application (logic) tier – The web server and logic associated with
generating dynamic web content, e.g., collecting and formatting the
results of a search.
- Data tier – A database.
6-Tier Web Application Architecture
The Application tier is often subdivided into two tiers:
- Business logic tier – Models the business objects associated with the application, e.g., accounts, inventories, etc., and captures the business rules and workflows associated with how these processes can be processed and manipulated.
- Data access tier – Responsible for accessing data, and passing it to the business logic tier, e.g., account balances, transactions, etc.
The Presentation tier is often subdivided into two tiers:
- Client tier – client-side user interface components.
- Presentation logic tier – server-side scripts for generating web pages.
Finally, the web server is often separated out into its own Web tier.
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