CLIENT SERVER ARCHITECTURE:
Client-Server Architecture is an architectural deployment style that describe the separation of functionality into layers with each segment being a tier that can be located on a physically separate computer. They evolved through the component oriented approach, generally using platform specific methods for communication instead of a message-based approach.
This architecture has different usages with different applications. It can be used in web applications and distributed applications. The strength in particular is when using this architecture over distributed systems. In this course work, I will furthermore invest this through the example of three-tier architecture in web applications.
Structure
Using this architecture the software is divided into 3 different tiers: Presentation tier, Logic tier, and Data tier. Each tier is developed and maintained as an independent tier.
1**-Presentation tier
This is the topmost level of the application. The presentation layer provides the application’s user interface (UI). Typically, this involves the use of Graphical User Interface for smart client interaction, and Web based technologies for browser-based interaction. The presentation tier displays information related to such services as browsing merchandise, purchasing, and shopping cart contents. It communicates with other tiers by outputting results to the browser/client tier and all other tiers in the network.
2-Logic tier (called also business logic, data access tier, or middle tier)
The logic tier is pulled out from the presentation tier and, as its own layer; it controls an application’s functionality by performing detailed processing. Logic tier is where mission-critical business problems are solved. The components that make up this layer can exist on a server machine, to assist in resource sharing. These components can be used to enforce business rules, such as business algorithms and legal or governmental regulations, and data rules, which are designed to keep the data structures consistent within either specific or multiple databases. Because these middle-tier components are not tied to a specific client, they can be used by all applications and can be moved to different locations, as response time and other rules require. For example, simple edits can be placed on the client side to minimize network round-trips, or data rules can be placed in stored procedures.
3-Data tier
This tier consists of database servers, is the actual DBMS access layer. It can be accessed through the business services layer and on occasion by the user services layer. Here information is stored and retrieved. This tier keeps data neutral and independent from application servers or business logic. Giving data its own tier also improves scalability and performance. This layer consists of data access components (rather than raw DBMS connections) to aid in resource sharing and to allow clients to be configured without installing the DBMS libraries and ODBC drivers on each client. An example would be a computer hosting a database management system (DBMS), such as a Microsoft SQL Server database.
Components Interconnections:
3 tier application architecture is characterized by the functional decomposition of applications, service components, and their distributed deployment, providing improved scalability, availability, manageability, and resource utilization. During an application’s life cycle, the three-tier approach provides benefits such as reusability, flexibility, manageability, maintainability, and scalability. Each tier is completely independent from all other tiers, except for those immediately above and below it. You can share and reuse the components and services you create, and you can distribute them across a network of computers as needed. You can divide large and complex projects into simpler projects and assign them to different programmers or programming teams. You can also deploy components and services on a server to help keep up with changes, and you can redeploy them as growth of the application’s user base, data, and transaction volume increases.
Logic layer is moved outside the presentation layer and into the business layer as it enhances reuse. As applications grow, applications often grow into other realms. Applications may start out as a web application, but some of the functionality may later be moved to a smart client application. Portions of an application may be split between a web site and a web or windows service that runs on a server. In addition, keeping logic helps aid in developing a good design (sometimes code can get sloppier in the UI).
The main benefits of the 3-tier architectural style are:
Maintainability. Because each tier is independent of the other tiers, updates or changes can be carried out without affecting the application as a whole.
Scalability. Because tiers are based on the deployment of layers, scaling out an application is reasonably straightforward.
Flexibility. Because each tier can be managed or scaled independently, flexibility is increased.
Availability. Applications can exploit the modular architecture of enabling systems using easily scalable components, which increases availability.
Consider the 3-tier architectural style if the processing requirements of the layers in the application differ such that processing in one layer could absorb sufficient resources to slow the processing in other layers, or if the security requirements of the layers in the application differ. For example, the presentation layer should not store sensitive data, while this may be stored in the business and data layers. The 3-tier architectural style is also appropriate if you want to be able to share business logic between applications, and you have sufficient hardware to allocate the required number of servers to each tier.
The client server architectures are of three types
- Filer Server Architecture
Database Server Architecture
Three-tier Architecture
FILE SERVER ARCHITECTURE
The first client server architecture being developed is the file server architecture., all processing will be done at the PC that requested the data that is client handles the presentation logic, the processing logic and much of the storage logic. That means out of t he hundred percent work that need to be done every logics that we have seen application logics that we have seen like presentation ;logic, processing logic and storage logic more than 80% of the job it will be carried out at the client side itself. So that is what I am trying to say here. All processing is done at the PC that requested the data that is client handles the presentation ;logic processing logic and much of the storage logic. A file server is a device that manage sonly the file operation and shared by each of the client PCs attached to the local area network. Each filer server acts as a n additional hard disk so wherever I am talking about a file server every file server will be ac5ring as an extra hard disk which will be present not only at the server level and which will also be present at the client side. For each of the client PC. Each PC maybe called a fat client because this client does an extensive work based on that I am calling this client as a fat client so most of the processing since it happens at the client side it is called fat client. Entire file are transferred from the server to the client for processing. So anything that the client has requested that query will be taken by the server and the server will respond all the possible states back to the server without any processing and client after the client receives all the service or the files requested for processing the client executes everything and it will be called a process.
DATABASE SERVER ARCHITECTURE:
It is similar to data warehouse where the website store or maintain their data and information. A Database Server is a computer in a LAN that is dedicated to database storage and retrieval. The database server holds the Database Management System (DBMS) and the databases. Upon requests from the client machines, it searches the database for selected records and passes them back over the network.
A database server can be defined as a server dedicated to providing database services. Such a server runs the database software. A database server can typically be seen in a client-server environment where it provides information sought by the client systems.
Three-tier Architecture
Three-tier architecture is a well-established software application architecture that organizes applications into three logical and physical computing tiers: the presentation tier, or user interface; the application tier, where data is processed; and the data tier, where the data associated with the application is stored and managed.
The chief benefit of three-tier architecture is that because each tier runs on its own infrastructure, each tier can be developed simultaneously by a separate development team, and can be updated or scaled as needed without impacting the other tiers.
