Uml Three Tier Architecture Diagram

Architectural Design

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Introduction to Architectural Design

• Architectural design is an abstraction of system which defines the system elements and how they interact.
• It is a structure of the system which describes software elements, properties of those elements and relationships between them.
• It provides a design plan to manage the complexity of a system and also a communication medium between stakeholders.
• An architectural design is used as a blueprint during the development process.
• Architectural design decisions have considerable impact on the quality, performance, maintainability and overall success of the application.

Importance of Architectural Design

1. Performance

• The right architecture covers the way for system success and the wrong architecture usually causes some form of disaster.
• Performance depends on raw processing power of its hardware and is important to make the system successful.
• It helps to validate software architectural design choices with respect to performance indices.

2. Scalability

• Scalability of the system is related to performance.
• It considers how quickly the system performs its current workload.
• It focuses on the predictability of the system's performance as the workload increases.

3. Reliability

• Reliability is the probability of failure free software architecture design.
• It is an important factor affecting on system reliability.

4. Security

• Security provides method to deal with requirements.
• It helps to manage the risk which may be arises in architectural design.

5. Modifiability

• It is possible to make minor changes in the architectural design.

6. Reusability

• Reusability makes easy to reuse the code in a new system.

Architecture Views

• Architectural views are representations of the overall architecture.
• Architectural views are meaningful to one or more stakeholders in the system.
• It is based on the use of multiple, concurrent views.

4+1 View Model

• 4+1 view model is used for describing the architecture of software intensive system.
• This model is based on the use of multiple concurrent views.
• These views are used to describe the system from the viewpoint of different stakeholders, such as end-users, developers and project managers.

There are four views of the model,

1. Logical View
2. Process View
3. Development View
4. Physical View

Why is it called 4 + 1 instead of just 5?

• Use cases are used to illustrate the architecture serving as the + 1 view. Hence, the model contains 4 + 1 views.
• When all the views are finished, use cases are effectively redundant.
• This model gives the detail of high requirements of the system.

1. Logical View

• Logical view contains the information about the various parts of the system.
• It is concerned with the functionality that the system provides to end-users.
• UML diagrams are used to represent logical view, including class diagram, communication diagram, sequence diagram.

2. Development View

• Development view is also known as the Implementation view.
• It illustrates a system from a programmer's perspective.
• It is concerned with the software management.
• It focuses on software modules and subsystems.
• UML diagrams are used to represent development view, including package diagram, component diagram.

3. Process View

• Process view deals with the dynamic aspects of the system.
• It explains the system process, how they communicate and focuses on the runtime behavior of the system.
• It describes the concurrent process within the system.
• UML diagrams are used to represent process view, included in the activity diagram.

4. Physical View

• Physical view is also known as the Deployment view.
• It describes the physical deployment of the system.
• It depicts the system from a system engineer's point of view.
• UML diagrams are used to represent physical view, included in the deployment diagram.

5. Use Case View

• Use case view describes the functionality of the system from the perspective of the outside world.
• It contains the diagram describing what the system is supposed to do from a black-box perspective.
• It contains use case diagrams.
• This view can guide all other views.

Client-Server Architecture

• Client-Server Architecture is a network in which the server hosts, delivers and manages most of the resources and services to be consumed by the client.
• Client-Server Architecture has one or more client/user computers connected to a central server over a network.
• In this architecture, the server acts as the producer and the client as a consumer.

The above figure shows two tier client-server architecture, where it works when the client computer sends a request to the server over the network / Internet connection and then delivered to the client.

Server manages several clients simultaneously, whereas one client can be connected to several servers at a time and each server providing different set of services.

• Internet is based on client-server architecture where the web server serves many simultaneous clients or users with web page or website data.
• This architecture describes the relationship between a client and one or more servers, where the client initiates one or more requests, waits for replies and processes the replies.
• Server authorizes the client or user and then send responses to communicate information to the client.

Following are the variations of client-server architecture include,

1. Client-Queue-Client Systems
2. Peer-to-Peer (P2P) Applications
3. Application Servers

1. Client-Queue-Client Systems

• Client-Queue-Client system allows client to communicate with other clients through a server-based queue.
• It allows client to distribute and synchronize files and information.

2. Peer-to-Peer (P2P) Applications

• Peer-to-Peer application allows client and server to swap their roles in order to distribute and synchronize the files and information across multiple clients.
• This approach extends the client/server style through multiple responses to requests, shared data, resource discovery.

3. Application Servers

• In this approach, client executing an application which runs on the server through a framework such as Terminal services.

Client-Server Architecture Models

There are two models of Client-Server Architecture,

1. Thin Model
2. Thick Model

1. Thin Model

• Thin model is used when legacy systems are migrated to client-server architecture where legacy system acts as a server and implemented on a client with a graphical interface.
• It includes all the application processing and data management is carried by the server.
• This model has major disadvantage is that it places heavy processing load on both the server and the network.

2. Thick Model

• Thick model is also known as Fat Client Model.
• This model is good for new client-server systems.
• Thick model is more complex than a thin model.

Advantages of Client-Server Architecture

• Client-Server architecture provides higher security. All the data is stored on the server so the control of security is greater than client machines.
• It accesses centralized data because the data is stored only on the server.
• It ensures the ease of maintenance where a client remains and unaffected by a server repair, upgrade or relocation.
• Client-Server architecture simplifies the design and the development of distributed applications.

Disadvantages of Client-Server Architecture

• Client-Server architecture has traffic congestion problem when a large number of clients send requests to the same server.
• If server fails then user will not be able to request to the network until the server is fixed or replaced. It has lack of robustness because of centralized server.

Multi-Tier/N-Tier Architecture

• Multi-Tier architecture is also known as 3 tier or N-tier architecture.
• It is a client-server architecture developed and distributed between more than one layer.
• This architecture provides a model by which developers can create flexible and reusable applications.
• This architecture is composed of a Presentation tier, an Application tier and a Data Storage tier.

1. Presentation Tier

• Presentation tier is the top-most level of the application.
• This tier displays the information related to such services as browsing, purchasing, shopping cart contents.
• Presentation tier communicates with other tiers which display the results to the client tier.
• This tier translates the task and makes the result to something the user can understand.

2. Application Tier

• Application tier is also known as Business Logic, Logic Tier and Middle Tier.
• Application tier is pulled out from the Presentation Tier.
• This architecture controls an application's functionality by performing detailed processing.
• Business tier coordinates the application, processes commands, makes logical decisions and performs calculations.

3. Database Tier

• Database tier includes database servers, file shares etc.
• This tier provides an API to the Application Tier.
• In this tier, the information is stored and retrieved from a database or file system then the information is passed back to the logic tier for processing and eventually back to the user.

Advantages of Multi-Tier Architecture

• Multi-Tier architecture is simple to manage and gives better performance than a Thin client.
• This architecture enhances the reusability and scalability.
• It reduces network traffic.
• It provides multithreading support, maintainability and flexibility.

Disadvantages of Multi-Tier Architecture

• Multi-Tier architecture has critical server reliability and availability.
• Testing cannot be performed well due to lack of testing tools.

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