topic Re: Definitions in Application Development and Automation Discussions

Definitions

Former Member — Mon, 30 Oct 2006 08:46:08 GMT

Hi ,

What is client server architecture ?

What is 2 Tier architecture ?

What is 3 Tier Architecture ?

What is Difference between Client Server , 2 Tier Arch

What is Difference Between Client Server , 3 Tier Arch

What is Difference Between 2 Tier , 3 Tier Arch

Points wil be assigned definetly

Regrads

Re: Definitions

Former Member — Mon, 30 Oct 2006 08:48:40 GMT

SAP architecture depends on what SAP products you have. For R/3 it is three-tiered, hence the name. The tiers are database, application and presentation.

2 tier architecture includes database and presentation layer where as 3 tier include application layer with database and presentation layers..

REgards,

Santosh

Message was edited by: Santosh Kumar Patha

Re: Definitions

Former Member — Mon, 30 Oct 2006 08:49:05 GMT

2 tier means presentation server , database.

3 tier means presentation server , application server , database.

Re: Definitions

Former Member — Mon, 30 Oct 2006 08:54:57 GMT

Hi,

1. client/server architecture

A network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power.

In brief, One server which maintains database and more than one client who serve as front end and communicates with server.

2. Client/server architecture sometimes called as 2-tier architecture.

Eg.

Presentation server

Database server

3. 3 Tier architecture is distributed over 3 stages.

SAP R/3 is 3 tier architecture.

Presenatation server

Database server

Application server (OS level)

This is brief information.

For better understanding use SAP Help

Hope this helps you to start on.

Re: Definitions

Former Member — Mon, 30 Oct 2006 08:57:48 GMT

Client server :

A request , Response between 2 systems.

But 3 Tier Architecture also uses this , Even if 3 servers are involved only 2 systems contact at a time

Request

Presentation - > Application

Application --> Database

Response

Database --> Application

Application --> Presentation

So what is difference between client server , 3 Tier

Regards

Re: Definitions

seshatalpasai_madala — Mon, 30 Oct 2006 08:59:27 GMT

HI,

Client server architecure is nothing butwe have two system The system which needs a service(Client) and the system which provides a service(Server).

We can have to point of views of both Hardware and Software.

In Hardware.

we have on system which acts as a server and lots of clients who connect to that server for resources.

In Software.

We have a server program (Webserver) which is installed on a system. Then we have a client program (Web browser) which sends request to the server program. In this case both server an client can be on a single machine. As you can install server as well as browser on the same system.

Coming to 2 tier.

We have One layer of presentation server layer

and another layer of Application and Database layer.

3 tier we have

One layer of presentation servers,

one layer of applications servers,

One layer of database server.

SAP R/3 uses this 3 tier model Hence R/3.

Regards,

Sesh

Re: Definitions

Former Member — Mon, 30 Oct 2006 09:03:06 GMT

Client/server is two programs talking to each other.

With client/server, the client and server programs are independent processes. If the client sends a request to the server, it is free to perform other work while waiting for the response.

When the client and server programs both run on the same computer, the configuration is referred to as single-tier client/server. (A tier is the boundary between two computers.) When they run on different computers, the configuration is referred to as two-tier client/server.

A program can function as both a client and a server if it both requests information and replies to requests. When you have three programs in communication the configuration is called three-tier client/server.

The client/server configuration enables the R/3 system to spread its load across multiple computers. This provides the customer with the ability to scale the processing power of the system up or down by simply adding another computer to an existing configuration, instead of replacing a single computer that performs all of the processing, such as that which occurs in the mainframe world.

SAP based the architecture of R/3 on a three-tier client/server model.

Presentation Server

The presentation server is actually a program named sapgui.exe. It is usually installed on a user's workstation. To start it, the user double-clicks on an icon on the desktop or chooses a menu path. When started, the presentation server displays the R/3 menus within a window. This window is commonly known as the SAPGUI, or the user interface (or simply, the interface). The interface accepts input from the user in the form of keystrokes, mouse-clicks, and function keys, and sends these requests to the application server to be processed. The application server sends the results back to the SAPGUI which then formats the output for display to the user.

Application Server

An application server is a set of executables that collectively interpret the ABAP/4 programs and manage the input and output for them. When an application server is started, these executables all start at the same time. When an application server is stopped, they all shut down together. The number of processes that start up when you bring up the application server is defined in a single configuration file called the application server profile.

Each application server has a profile that specifies its characteristics when it starts up and while it is running. For example, an application sever profile specifies:

Number of processes and their types

Amount of memory each process may use

Length of time a user is inactive before being automatically logged off

The application server exists to interpret ABAP/4 programs, and they only run there-the programs do not run on the presentation server. An ABAP/4 program can start an executable on the presentation server, but an ABAP/4 program cannot execute there.

If your ABAP/4 program requests information from the database, the application server will format the request and send it to the database server.

Database Server

The database server is a set of executables that accept database requests from the application server. These requests are passed on to the RDBMS (Relation Database Management System). The RDBMS sends the data back to the database server, which then passes the information back to the application server. The application server in turn passes that information to your ABAP/4 program.

There is usually a separate computer dedicated to house the database server, and the RDBMS may run on that computer also, or may be installed on its own computer.

Configuration of servers

In a three-tier client/server configuration, the presentation servers, applications servers, and database server all run on separate machines. This is the most common configuration for large systems, and is common in production.

In the distribution presentation configuration, the application and database servers are combined on one computer and the presentation servers run separately. This is used for smaller systems, and is often seen on a development system.

In the two-tier client/server configuration, the presentation and application servers are combined and the database server is separate. This configuration is used in conjunction with other application servers. It is used for a batch server when the batch is segregated from the online servers. A SAPGUI is installed on it to provide local control.

When all servers are combined onto a single machine, you have a central configuration. This is rarely seen because it describes a standalone R/3 system with only a single user.

The simplest definition of an R/3 system is "one database." In one R/3 system, there is only one database. To expand the definition, R/3 is considered to be all of the components attached to that one database. One R/3 system is composed of one database server accessing a single database, one or more application servers, and one or more presentation servers. By definition, it is all of the components attached to one database. If you have one database, you have one system. If you have one system, you have one database. During an implementation, there is usually one system (or one database) assigned to development, one or more systems designated for testing, and one assigned to production.

I hope it helps.

Best Regards,

Vibha

*Please mark all the helpful answers

Re: Definitions

anversha_s — Mon, 30 Oct 2006 09:20:43 GMT

hi,

Client/server architecture.

As a result of the limitations of file sharing architectures, the client/server architecture emerged. This approach introduced a database server to replace the file server. Using a relational database management system (DBMS), user queries could be answered directly. The client/server architecture reduced network traffic by providing a query response rather than total file transfer. It improves multi-user updating through a GUI front end to a shared database. In client/server architectures, Remote Procedure Calls (RPCs) or standard query language (SQL) statements are typically used to communicate between the client and server

The remainder of this write-up provides examples of client/server architectures.

Two tier architectures. With two tier client/server architectures (see Two Tier Software Architectures), the user system interface is usually located in the user's desktop environment and the database management services are usually in a server that is a more powerful machine that services many clients. Processing management is split between the user system interface environment and the database management server environment. The database management server provides stored procedures and triggers. There are a number of software vendors that provide tools to simplify development of applications for the two tier client/server architecture [Schussel 96, Edelstein 94].

The two tier client/server architecture is a good solution for distributed computing when work groups are defined as a dozen to 100 people interacting on a LAN simultaneously. It does have a number of limitations. When the number of users exceeds 100, performance begins to deteriorate. This limitation is a result of the server maintaining a connection via "keep-alive" messages with each client, even when no work is being done. A second limitation of the two tier architecture is that implementation of processing management services using vendor proprietary database procedures restricts flexibility and choice of DBMS for applications. Finally, current implementations of the two tier architecture provide limited flexibility in moving (repartitioning) program functionality from one server to another without manually regenerating procedural code.

Three tier architectures. The three tier architecture emerged to overcome the limitations of the two tier architecture. In the three tier architecture, a middle tier was added between the user system interface client environment and the database management server environment. There are a variety of ways of implementing this middle tier, such as transaction processing monitors, message servers, or application servers. The middle tier can perform queuing, application execution, and database staging. For example, if the middle tier provides queuing, the client can deliver its request to the middle layer and disengage because the middle tier will access the data and return the answer to the client. In addition the middle layer adds scheduling and prioritization for work in progress. The three tier client/server architecture has been shown to improve performance for groups with a large number of users (in the thousands) and improves flexibility when compared to the two tier approach. Flexibility in partitioning can be a simple as "dragging and dropping" application code modules onto different computers in some three tier architectures. A limitation with three tier architectures is that the development environment is reportedly more difficult to use than the visually-oriented development of two tier applications Recently, mainframes have found a new use as servers in three tier architectures

rgds

anver

pls mark all hlpful answers

Re: Definitions

Former Member — Mon, 30 Oct 2006 10:07:03 GMT

I Assigned points to all.