Sql Server Architecture

Chapter 7 - Client/Server Architecture
Microsoft SQL Server is designed to work effectively in a number of environments:
* As a two-tier or multitier client/server database system 
* As a desktop database system 
Client/Server Database Systems 
Client/server systems are constructed so that the database can reside on a central computer, known as a server, and be shared among severalusers. Users access the server through a client or server application:
* In a two-tier client/server system, users run an application on their local computer, known as a client, that connects over a network to the server running SQL Server. The client application runs both business logic and the code to display output to the user, and is also known as a thick client. 
In a multitierclient/server system, the client application logic is run in two locations:
* The thin client is run on the user's local computer and is focused on displaying results to the user. 
* The business logic is located in server applications running on a server. Thin clients request functions from the server application, which is itself a multithreaded application capable of working with manyconcurrent users. The server application is the one that opens connections to the database server and can be running on the same server as the database, or it can connect across the network to a separate server operating as a database server. 
This is a typical scenario for an Internet application. For example, a server application can run on a Microsoft Internet Information Services (IIS) andservice thousands of thin clients running on the Internet or an intranet. The server application uses a pool of connections to communicate with a copy of SQL Server. SQL Server can be installed on the same computer as IIS, or it can be installed on a separate server in the network. 
Having data stored and managed in a central location offers several advantages:
* Each data item is stored in acentral location where all users can work with it. 
Separate copies of the item are not stored on each client, which eliminates problems with users having to ensure they are all working with the same information. 
* Business and security rules can be defined one time on the server and enforced equally among all users.
This can be done in a database through the use of constraints, storedprocedures, and triggers. It can also be done in a server application. 
* A relational database server optimizes network traffic by returning only the data an application needs.
For example, if an application working with a file server needs to display a list of the names of sales representatives in Oregon, it must retrieve the entire employee file. If the application is working with a relationaldatabase server, it sends this command: 
SELECT first_name, last_name
FROM employees
WHERE emp_title = 'Sales Representative'
AND emp_state = 'OR'
The relational database sends back only the names of the sales representatives in Oregon, not all of the information about all employees. 
* Hardware costs can be minimized.Because the data is not stored on each client, clients do not have to dedicate disk space to storing data. The clients also do not need the processing capacity to manage data locally, and the server does not need to dedicate processing power to displaying data. 
The server can be configured to optimize the disk I/O capacities needed to retrieve data, and clients can be configured to optimize theformatting and display of data retrieved from the server. 
The server can be stored in a relatively secure location and equipped with devices such as an Uninterruptable Power Supply (UPS) more economically than fully protecting each client. 
* Maintenance tasks such as backing up and restoring data are simplified because they can focus on the central server. 
In large client/server systems,...