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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:
1) 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.
2) 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.
3) 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.
4) 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.
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:
- Common User Access (CUA) defines conventions for GUI look and feel.
- Common Programming Interface (CPI) provides languages, tools, and APIs that give applications greater portability and more consistent user interfaces across multiple platforms.
- Common Communication Support (CCS) supports existing communications standards, such as LU 6.2.
- Common Applications, written by IBM, will serve as demonstrations of SAA concepts and make it easy for users to migrate between systems.
Subject: 3.8 What is APPLE's VITAL architecture?
VITAL provides a way of building information systems constructed from generalized modules that can be reused and shared.It specifies how to construct and provide interfaces for these modules. A cornerstone of Apple's client/server architecture is Data Access Language (DAL).DAL sits between the client and server components. With DAL, a change in the DBMS does not affect the front-end; it simply requires the appropriate DAL link.
Subject: 3.9 What is Sun's Open Network Computing Architecture?
Open Network Computing (ONC) is the Sun architecture,with third party alliances providing the missing pieces.Transport Independent Remote Procedure Calls (TI-RPC) were co-developed by Sun and AT&T. TI-RPC runs independent of the underlying network transport, allowing applications to run unmodified over multiple transport protocols including NetWare,PCNFS, AIX/6000, Solaris, UNIX/SVR4, AIX/ESA.
Subject: 3.10 What is Digital's Network Application System (NAS) architecture?
NAS is a software suite that enables applications to be integrated across a distributed network of multivendor systems: NAS services are divided into four main groups:
- Application Access Services which support user interface (forms based , graphical or character terminal based).
- Communication and Central services which support communications using electronic mail and EDI.
- Information and resource sharing, which supports database access and compound documents (collection of images, graphics and conventional text).
- System Access services which provides a standard operating system interface
Subject: 3.11 What is OSF-DCE?
DCE is the Distributed Computing Environment, from the Open Software Foundation. (It is called "the DCE" by sticklers for grammatical consistency.
DCE consists of multiple components like Remote Procedure Call( RPC),the cell and global directory services(CDS and GDS),the security service,DCE threads,Distributed Time Service(DTS) and Distributed File Service(DFS) which have been integrated to work closely together.DCE is called "middleware" or "enabling technology." It is not intended to exist alone, but instead should be integrated or bundled into a vendor's operating system offering.
Subject: 3.12 What are Distributed Object Management Systems (DOMS)?
DOMS provide a way of pulling diverse components together and managing their communications. They are aimed at addressing the following:
- A single interface to manage the complexities of a heterogeneous environment
- A uniform framework, based on standards and extensibility, to build, integrate , and deploy open distributed-computing applications
- A method for creating location independence for client applications.
Subject: 3.13 What is CORBA?
CORBA stands for the Common Object Request Broker Architecture. It is a set of standard mechanisms for naming, locating, and defining objects in a distributed computing environment.
Subject: 3.14 What is DAE?
Distributed Application Environment is designed to allow businesses to use IBM's RISC System/6000 and PS/2 computers in a client/server network (or standalone) for their business applications. DAE consists
(1) MESSAGING
services;
(2) DATABASE services ;
(3) PRESENTATION services;
(4) DEVICE services to capture data and to control a broad category of controllers, devices, equipment and sensors.
Subject: 4.1 Business-Focused Client/Server Architecture When analysing a business there are three views of the organisation:
A functional model, which reflects organisational responsibilities and the way in which the people who use the system view their work.
A process model, which details the business functions of the organisation (eg accept orders, make goods, deliver goods, bill customers, receive money). The
functional structure and process model rarely, if ever, agree. - An information model, which details the information that the organisation needs to function.
Subject: 4.2. Client/Server Business Application Architectures
Traditional applications architectures should reflect the complete range of business requirements have been based on function. Therefore, client/server computing demands a three layer view of the organisation. 1 The user interface layer, which implements the functional model 2 The business function layer, which implements the process model 3 The data layer, which implements the information model This application architecture does not demand multiple
hardware platforms, although such technology can be utilised
Subject: 4.3 Business Drivers
Client/server computing has arisen because of a change in business needs. Businesses today need integrated,flexible, responsive and comprehensive applications to support the complete range of business processes.Problems with existing systems include:
applications were developed to model vertical applications - applications were built in isolation
applications were implemented as monolithic systems
applications were complex
the supporting technology was based on a centralised control model Information technology, which is an enabling factor in systems building, has almost reached the stage where these systems can be designed and created. The development and implementation of client/server computing is more complex,more difficult and more expensive than traditional, single process
applications. The only answer to the question "why build client/server applications?" is "because the business demands the increased benefits.
Subject: 4.4 Business Benefits
There is a perceived need for vendor independence including application development methodologies,programming paradigms, products and architectures.
Organisation have changed from steep hierarchies to flattened hierarchies
Network management is replacing vertical management
There is a change to team based management
The customer should have a single point of contact for all business with the organisation
The customer should deal with the same person over multiple contacts
The user will perform as much processing as possible during customer contact time
The time required to complete the work will be minimised
There is a need for empowerment of staff and audit trail of actions
Multi-skilled and multi-function teams need access to multiple applications
Subject: 4.5 What does business expect from IT?
New applications should be aligned with both the user's view and the business process view. Existing functionally aligned systems are not appropriate
Applications need to provide a consistent user interface
Application complexity needs to be hidden
The user interaction must be flexible
Consistent information across all applications
A variety of user interface styles to reflect the needs of the work
Users should be able to modify business rules without reference to IT staff
IT systems will support all activity performed by the user, not just a part
An ability to evolve IT systems to reflect changing business requirements
It is essential that there be integrity of transactional processes
Subject: 4.6 What is Business Process Reengineering?
Reengineering is the organizational process required to align
people, processes and technology with strategies to achieve
business integration. It can also be thought of as taking a
business in its current state and forming an organizational
and operational blueprint to redirect skills, policies, information
(data), cultural values, organizational structures, processing and
incentives towards targeted improvements.
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