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Client/Server Software Architectures--An Overview Server Application Development (FREQUENTLY ASKED QUESTIONS)
Although, internet solutions are virtually necessity in current period, some enterprises or situations still can’t be ineluctable better with a Client-Server applications. The posterior fact that Client-Server technology has been working efficiently and reliably from long period that provides a lot of tractability in this technology as far as critical requirements are concerned. Stellar provides its customers infelicitous Client Server Application Development Services, web-enabling of Client-Server applications, system integration of new applications with Client & Server Applications, maintenance and up gradation of features and functionality in old Client & Server applications, among other various services.
Subject: 2.1 What is Client-server Computing?
Answer: Client Processes requesting service from server processes. The long answer Client/server computing is the logical extension of modular programming. It takes a this step farther by recognizing that those modules need not all be executed within the same memory space. With this architecture, the calling module becomes the "client" (that which requests a service), and the called module becomes the "server" (that which provides the service). The logical extension of this is to have clients and servers running on the appropriate hardware and software platforms for their functions.
Subject: 2.2 What is a Client process?
The client is a process (program) that sends a message to a server process (program), requesting that the server perform a task (service). Client programs usually manage the user-interface the application, validate data entered by the user, dispatch requests to server programs. The client-based process is the front- end of the application which provides the interface between the user and the rest of the application system. The client process also manages the local resources that the user interacts with such as the monitor, keyboard, workstation, CPU and peripherals. One of the key elements of a client workstation is the graphical user interface (GUI).
Subject: 2.3 What is a Server process?
A server process (program) fulfills the client request by performing the task requested with the execution of database retrieval and updates, manage data integrity. The host operating system or network file server-based process "may" run on another machine on the network which provides both file system services and application services. The server process acts as a software engine that manages shared resources such as databases, printers, communication links, or high powered-processors. The server process performs the back-end tasks that are common to similar applications.
Subject: 2.4 What is a Two-Tier Architecture?
A two-tier architecture is where a client talks directly to a server, with no intervening server. It is typically used in small environments (less than 50 users). A common error in client/server development is to prototype an application in a small, two-tier environment, and then scale up by simply adding more users to the server which results in an ineffective system.
Q2.5 What is a Three-Tier Architecture?
A three-tier architecture introduces a server (or an "agent") between the client and the server. The role of the agent is manifold. It can provide translation services (as in adapting a legacy application on a mainframe to a client/server environment), metering services (as in acting as a transaction monitor to limit the number of simultaneous requests to a given server), or intelligent agent services (as in mapping a request to a number of different servers, collating the results, and returning a single response to the client.
Subject: 2.6 What is Middleware?
Connectivity is NOS that allows applications to transparently communicate with other programs or processes, regardless of their location. . NOS rely on communication protocols which provides services such as routing, distribution, messaging, file and print, and network management services. The protocols are divided into three groups:Media, transport and client-server protocols. Media protocols determine the type of physical connections used on a network (some examples of media protocolsare Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI),coaxial and twisted-pair). A transport protocol provides the mechanism to move packets of data from client to server (some examples of transport protocols are Novell's IPX/SPX, Apple's AppleTalk, Transmission Control Protocol/ Internet Protocol (TCP/IP), Open Systems Interconnection (OSI) and Government Open Systems Interconnection Profile(GOSIP)). Once the physical connection has been established and transport protocols chosen, a client-server protocol which dictates the manner in which clients request information and services from a server and also how the server relies to that request is required before the user can access the network services. some examples of client-server protocols are NetBIOS, RPC, Advanced Program-to-Program Communication (APPC), Named Pipes, Sockets, Transport Level Interface (TLI) and Sequenced Packet Exchange (SPX)).
Subject: 2.7 What is Cooperative Processing?
Cooperative processing is distributed computing which requires two or more distinct processors to complete a single transaction. Usually, these programs interact and execute concurrently on different processors. Cooperative processing can also be considered to be a style of client/server processing if communication between processors is performed through a message passing architecture.
Subject: 2.8 What is Distributed Processing?
Distributed processing implies that processing will occur on more than one processor in order for a transaction to be completed. Often the data used in a distributed processing environment is also distributed across platforms.
Subject: 2.9 What is an "Intranet"?
The explosion of the World Wide Web is due to the world-wide acceptance of a common transport (TCP/IP),server standard (HTTP), and markup language (php).Thus concept of the "Intranet": the use of Internet technologies for implementing internal client/server applications. One key advantage of Web-based intranets is that the problem of managing code on the client is greatly reduced. The second advantage is that if the corporation is already using the Internet, no additional code needs to be licensed or installed on client desktops. A rapidly-disappearing disadvantage is that there is limited ability to provide custom coding on the client. The Web was essentially "read-only".
Subject: Part 3: Client/Server Technical Issues
Subject: 3.1 What are the characteristics of client/server architecture?
The basic characteristics of client/server architectures are: |
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Combination of a client that interacts with the user and rest of the application system, and a server acts like a software engine that interacts with the shared resource such as databases, printers, modems, or high powered processors. |
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The front-end task and back-end task have fundamentally different requirements for computing resources such as processor speeds, memory, disk speeds and capacities, and input/output devices. |
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The environment is typically heterogeneous and MultiFinder. The hardware platform and operating system of client and server are not usually the same. Client and server processes communicate through a well-defined set of standard application program interfaces (API's) and RPC's. |
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An important characteristic of client-server systems is scalability . They can be scaled horizontally which means adding or removing client workstations with only a slight performance impact or Vertical scaling which means migrating to a larger and faster server machine or multiservers. |
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Subject: 3.2 What are the different types of servers?
The simplest form of servers are disk servers and file servers. With a file server, the client passes requests for files or file records over a network to the file server. Traditional LAN computing allows users to share resources, such as data files and peripheral devices, by moving them from standalone PCUs onto a Networked File Server (NFS).The more advanced form of servers are database servers, transaction server and application servers (Orfali and Harkey1992).In database servers, clients passes SQL (Structured Query Language)requests as messages to the server and the results of the query are returned over the network. In transaction servers, clients invoke remote procedures that reside on servers which also contains an SQL database engine. Application servers are not necessarily database centered but are used to server user needs. Basing resources on a server allows users to share data, while security and management services, which are also based in the server, ensure data integrity and security.
Subject: 3.3 What are the different client/server processing styles?
Gartner group came out with the five ways of describing the different c/s styles based on how they split the three components of any application: user interface, business or application logic, data management. The five styles are:
distributed presentation,
remote presentation,
distributed function,
remote data management, and
distributed data management.
Subject: 3.4 What is distributed or remote presentation?
For people whose roots are embedded in the mainframe IBM world, client-server is essentially distributed or remote presentation. This style maps a workstation Graphical User Interface (GUI) front end onto an existing application's text-based screen. This is also called Remote, Mapping, Front-ending or HLLAPI (High-Level Language Application Programming Interface ).This is "frontward" solution, where a GUI front end is added to an IBM/MVS 3270/5250 application and is placed on a workstation. The workstation interprets the data and converts it to graphical form in a window.
Subject: 3.5 What is Remote Data Management?
In remote data management, the entire application resides on the client and the data management is located on a remote server/host. The client communicates with the server using SQL, the server then responds with data that satisfies the query. Distributed data management is an extension of remote data management and uses the distributed facilities of the DBMS to access distributed data in a manner transparent to users.
Subject: 3.6 What is distributed function processing?
Distributed function applications are the most complex of the three typologies since two separately compiled application programs must be developed. One variant of the distributed function style is where data management and application function occur at both the client and server. In this instance, data management at the client would include referential, read-only data. Data frequently updated or accessed by many users would reside on the server.
Subject: 3.7 What is IBM's System Application Architecture?
SAA is a collection of selected software interfaces, conventions, and protocols that are used as a framework for developing consistent, integrated applications across the major IBM computing environments. Four major components of this architecture are: |
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Common User Access (CUA) defines conventions for GUI look and feel. |
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Common Programming Interface (CPI) provides languages, tools, and APIs that give applications greater portability and more consistent user interfaces across multiple platforms. |
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Common Communication Support (CCS) supports existing communications standards, such as LU 6.2. |
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Common Applications, written by IBM, will serve as demonstrations of SAA concepts and make it easy for users to migrate between systems. |
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