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Client-server Computer and latest buzzwords of the hottest industries
Chapter-1
Introduction: - Client / Server is one of the newest equipment and hottest buzzwords Industries. There is no generic definition of client / server, Showtracks used to number the nature, development and anticipateologies. However, the general idea is that clients and servers are logical entities that work in all the attention over a network to perform a task. Client-server is very fashionable. As such, it could just be a temporary fashion, but there is a general recognition that is fundamental and far-reaching, for example, the Gartner Group, which are the major industry analysts in this field have predicted that
"In 1995, client-server be synonymous with computing. "Most of the initial client / server success stories involve small-scale applications that provide direct or indirect access to transactional data in legacy systems. The business need to provide data access to decision makers, the relative immaturity of the client / server and tools technology, the changing use of wide area networks and lack of client / server experience make these companies attractive and low risk pilot. As organizations move up the learning curve of these small-scale projects to mission-critical applications, there is a corresponding increase in expectations of performance, uptime requirements and the need to remain flexible and scalable. In this challenging scenario, the choice and implementation of the architecture right is critical. In fact one of the fundamental questions that professionals have to deal with the beginning of each client / server project is - "What architecture is more suitable for this project - Level Two or Level Three?. "Interestingly, 17% of all mission-critical customer / server applications three levels and the trend is growing, according to Standish Group International, Inc., a market research firm. Architecture affects all aspects of software design and engineering. The architect considers the complexity of the application, the level of integration and interaction is necessary, the number of users, their geographical dispersion, the nature of networks and the global transactional needs of the application before deciding on the type of architecture. Inadequate design or improper implementation architecture can result in horrendous response times. The choice of architecture also affects the development time and flexibility in the future and maintaining the application. The current literature does not adequately address all these aspects of client / server architecture. This article defines the basic concepts of client / server architecture, describes the two levels and three architectures and discusses their respective advantages and limitations. Differences in development efforts, flexibility and ease of reuse is compared to a new aid in choosing an appropriate architecture for a given project.
Chapter-2
History and defintion -
History The University of Waterloo implemented Oracle Government Financials (OGF) in May 1996. That's basic accounting systems moved UW to a package supported by the manufacturer in a Solaris / Unix environment and away from locally developed package (s) in IBM / VM. Plans were now moving more (if not all) business systems to a single supplier and to standardize on a single database platform (Oracle for both). A very large state of the art system was purchased Solaris with the intention co-location of these other Oracle provides services in the same system with the OGF. Architecture of the safety net was intended to isolate administrative networks involved, the fire wall filters these networks trafficking protocol and asset tracking. The systems were purchased and deployed to implement the security architecture. Much has changed in the meantime. Although OGF now includes services beyond the set of 1996 plans to move all business systems failed. In particular, it takes People Soft / HRMS (Human Resources Management System) for the Payroll (shown in the fourth quarter 1998) with People Soft / SIS (Student Information Services) to follow a few years "Oracle still could not deliver these key components to our business. We also found that, although it is reasonable to require Oracle as the database when other applications specified, it is reasonable to expect to be certified with the same versions of Oracle Database and / or underlying operating system. Technology changes too quickly: the state of the art system Solaris is no longer current. The networks have been restructured to isolate the administrative systems in the Room "Red" and administrative users throughout the campus. However, the firewall administrative and asset monitoring traffic was never carried out - has recently been dismantled.
Definition: Despite the massive media coverage of client / server computing, there is much confusion about the definition of client / server is. Client and server are software and hardware entities. At its most fundamental, client / server software means an entity (client) of a specific request, which has completed, the other software entity (server). Figure 1 illustrates the client / server exchange. The client process sends a request to the server. The server interprets the message and then attempts to complete the application. In order to fulfill the request, the server may need to refer to a source of knowledge (database), process data (calculations) control of a peripheral, or make an additional request for another server. In both architecture, a client can make requests of multiple servers and a server can service multiple customers.
Figure 1 - Client / Server Transactions
It is important to understand that the relationship between the client and the server is a command / link control. In any given change, the client initiates the request and the server responds accordingly. A server can not initiate dialog with customers. Since the client and server are software entities that can be found in any appropriate hardware. A client process, for example, could be a resident in a network server hardware, and request data from a server process running on another server hardware or even a PC. In another scenario, the client and server processes can be found in the same physical hardware box. In fact, in the prototype stage, a developer can choose both the client and the presentation server and database on the same PC hardware. The server later can be migrated (distributed) to a more comprehensive system for the pre-production of additional evidence after most of the logic of the application and development of the data structure is complete. Although the client and the server can be found on the same machine, this paper mainly deals with architectures used to build applications distributed, ie those in which the client and server are on different physical devices. According to Beaver (et al.), A distributed application consists of separate parts that run on different nodes of the network and cooperate to achieve a common goal. The supporting infrastructure should also render the inherent complexity distributed processing invisible to the end user. The client in client / server architecture does not sport a graphical user interface (GUI) without But the mass-marketing of client / server has occurred largely due to the proliferation of customer graphical user interface. Some client systems / Server supports very specific functions, such as print queues (ie, the network print queues) or presentation services (eg X-Window). While these special-purpose implementations are important, this work is predominantly concerned with distributed client / server architectures that demand flexibility on functionality
Chapter-3
Meaning of client-server: -
Business sense of client-server: - Client-server is generally perceived as next step forward in the operational efficiency of business information systems. This is illustrated in Figure 1, indicating earnings of a succession of innovations. Computer companies began in the 1960s with batch processing. The main innovation of the 1970s was in line transaction processing (OLTP), which gathered information technology (IT) on the desktop, and made it an integral part of business processes. Batch processing and OLTP in combination remain at the core of enterprise information systems. Then in the 1980s came the personal computer, which was universally accessible and dispersed over business enterprises. Now, in the 1990s, client-server is generally perceived as the path of integration the different parts information systems back together. That is their role and importance.
Figure 1 Perceived impact on the client-server business in these circumstances a client-server (Or client / server) has become a popular brand that applies to almost all types of products, and all kinds of business and in technical and marketing messages. This tends to empty it of specific meaning, but in doing so actually confirmed its almost universal applicability.
Technical meaning of client-server: - A starting point useful for understanding client-server is the informal definition used by the Gartner Group:
"Client-server is the division of an application tasks that are performed on separate computers, one of which is a programmable workstation (eg a PC). "This definition says that a client-server on distributed computing and software architecture (applications are divided into tasks that can be on separate computers). It echoes the vital point is client-server how to integrate PC into all kinds of information systems.
Three generations of messaging:
Host-based architecture (not a client / server):
With mainframe software architectures all intelligence is within the central host computer. Users interact with the host through a terminal that captures keystrokes and sends that information to the host. Mainframe software architectures are not tied to one hardware platform. Interaction User can make use of personal computers and UNIX workstations. A limitation of mainframe software architectures is that they are easily converted interfaces support Graphical user or access to multiple databases of geographically dispersed sites. In recent years, mainframes have found a new use as a server in distributed client / server architectures
Lan file sharing architecture (not a client / server): - The original PC networks were based in file sharing architectures, where the server downloads files from the shared location to the desktop environment. The work required is the user runs (including logic and data) in the desktop environment. File sharing architectures work if shared usage is low, the update argument is low, and the volume of data transfer is low. In the 1990s, PC LAN (local area network) computing changed due to the capacity of the file sharing was strained as number of online users grew (which can only satisfy about 12 users simultaneously) and graphical user interfaces (GUIs) became popular (with the mainframe and terminal displays appear out of date). PCs are used in client / server architectures
Internet Client Server Architecture: - The objective of this class is build a knowledge base which underlies the rest of the course. In many areas of technology, one gets the impression that technology has always existed in its current form. But of course, technology has a history as any other natural or unnatural phenomenon. Therefore, it is on the Internet and World Wide Web. During this debate, let's look first at some of the significant developments that have taken place over the last thirty years that have made the Internet what it is today. After reviewing this chronology, we will see two of the underlying technologies that support the Internet. The first is Ethernet, the original local area network (LAN) and the technology continues being one of the most common communication systems used to connect computers that are within a few hundred yards of each other. The second is TCP / IP, the standard software that enables computers located around the world to direct messages to each other and communicate reliably. After discussing the Internet, then we will focus our attention on the World Wide Web, yes. The discussion begins with a review of its core customer-server architecture, in which a client program running on a computer communicates with a server running the program in another to request information or a service performed. The Web was built with an architecture client-server where a web browser (client) communicates with multiple web servers to request pages of information or a program is implemented through the Common Server Gateway Interface (CGI). As the Internet / WWW becomes a more general computing and communications infrastructure, this strict client server relationship is expanding. Such an expansion involves Java. Learn about recent events later in the course, but for now, we will concentrate on the classic Web client / server design. The language of Web clients and servers talk to each other is called HTTP (Hypertext Transfer Protocol). You do not have to learn HTTP in detail, but you will need to build basic HTTP messages in order to do CGI programming and you must understand its underlying philosophy and its basic form and capabilities.
Chapter-4
Process: -
Customer 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 portion of the application, validate data entered by the user, sending requests to server programs, and sometimes execute business logic. The client-based process is the front-end application the user sees and interacts with. The client process contains the logic of specific solutions and provides the interface between the user and the rest of the system application. The client process also manages the local resources that the user interacts with as the monitor, keyboard, CPU and peripherals workstation. One of the key elements of a client workstation is the graphical user interface (GUI). Typically, a portion of the operating system ie the window manager detects user actions, managing windows on the screen and displays the data in the windows.
The process server - A server process (program) complies with the request customer by performing the task requested. Server programs generally receive requests from client programs, execute database retrieval and updates integrity management data and send responses to client requests. Sometimes server programs execute common or complex business logic. The server-based process "May" run on another computer on the network. This server can be the host operating system or network file server, the server is then provided both services file system and application services. Or in some cases, another desktop machine provides the application services. The server process acts as a motor software that manages shared resources such as databases, printers, communication links, or high powered-processors. The server process performs the background tasks common to similar applications.
Client-Server Computing -
• A single client, single server
• Multiple clients, single server
Client / server is a computational architecture that involves client processes requesting service from server processes client / server is the logical extension of modular programming. Modular programming has as its fundamental premise that the separation of a large piece of software into its constituent parts ("Modules") creates the possibility for easier development and better maintainability. Client / server goes a step further by acknowledging that the modules need not be executed in the same memory space. With this architecture, the calling module becomes the "client" (a person requesting a service), and called module becomes the "server" (which provides the service). The logical extension of this is to have clients and servers running on hardware and software platforms for their functions. For example, database management system servers running on platforms specially designed and configured to perform questions or file servers running on platforms with special elements for managing files.
Network Computing Architecture: -
Architecture Oracle Network Computing (NCA) can be captured by three concepts:
1.This World Wide Web is a truly ubiquitous service.
2.The Java Virtual Machine is (or soon become) a truly ubiquitous service embedded in the browser.
3.A three-layer model for application delivery engine with Oracle Data Base (in a large Unix server), a lightweight Java application on the client, and a mid-level "forms" server to provide the gateway between the two.
Oracle began Release 10.7 NCA send (web-deployed applications) in January 1998 .... 2000 require
With Release 10.7 NCA, Oracle responded to the needs of users about the difficulty to Smart Client patches. Although the functionality is the same between 10 SC 10 and NCA, Oracle returns on the Web strategy deployed to relieve a more granular patch. This strategy also better preserves the customizations. Since the forms technology runs on the server in the statement of the deployed web, exceeds and regenerate after to patch is now easier. Due to differences in strategy patch, Oracle recommends that customers do not use Smart Client and Release 10.7 NCA in the same instance. Oracle will not support such a configuration. Customerncharactermode facilities should go directly to the deployed web release
Chapter-5
Client-Server Technology: - Client-server technology is better understood if we discussed in four areas:
1.Personal platforms
2.Server platforms
3.Client-server middleware
4.Client-server tools and services
Each of these areas is distinctive, although there may be overlap between them.
The term platform used here to refer to a computing platform that is a complete combination of hardware and operating system software.
personal platforms - personal platforms are perhaps the most distinctive part of the client-server technology. Is defined as a personal platform:
A computing platform, which is connected to a network, provides an intuitive user interface and consistent user help staff to carry out tasks on behalf of the company. These features are illustrated in Figure 2. personal platforms are relatively inexpensive and immensely powerful, and there is a wide choice of suppliers. Many different types of personal computers can be platforms (Eg MS / DOS PC, PC Windows, OS / 2 for PC, UNIX workstations, Apple Macintosh, and various handheld devices), but the most common case today day is an IBM compatible PC with Microsoft Windows operating system.
These platforms are universally accessible where needed. This has made the architecture computer systems from the inside out: the focus of age was the scarcity of resources in the central machine, far from its users, the new approach is the wealth of personal resources now at the fingertips of each individual user. This trend is a growing force, because the PC price / performance ratios continue to improve by a factor of two months each eighteen more or less. This shift is in line with changes in business structure: organizational hierarchies are being flattened, the authority making decisions are being transferred, and allowed "processes can now provide processes that were provided previously by office staff. A combined effect of these businesses trends and techniques is the training of the person at the desk. PCs offer a personal productivity and independence, but this individuality, multiplied by a large number of PCs, you can create anarchy. Client-Server helps solve these problems. The use of shared resources of the client (always on platforms server), not only personal resources, client-server structure allows all software and hardware resources on architecture and management control. Transform Computing between personal computing and personal computing across the enterprise. These features help to create the order, work group cohesiveness, productivity, and flexibility of business process. Despite personal platforms are the economic driving techniques and the main force for the move to client-server, are only the first of five technical ingredients identified at the beginning of Section 2.
Server Platforms -
It is defined as a server platform:
A computer platform that provides software services for use in other parts of the system. In short, the services are for personal use on platforms, but services are also available for use in other server platforms. A server platform can provide services through terminals that do not qualify as dependents personal platforms. Almost any computer platform can act as server platforms. Therefore, there are many different suppliers, and many possible types of platforms server, from supercomputers to PCs. Each is good for certain types of workloads, for different quality requirements, and in different areas of money and the spectrum performance. The user can select the various platforms to meet different needs. This breadth of choice is illustrated in Figure 3, which shows that the user in the personnel platform can access services in many server platforms. This also illustrates the shift in the individual user on a personal platform, now you can choose IT services from many different sources in other parts of the network. The polarization of the client systems and server platforms recognizes distinctions between personal and shared resources. Each platform is a remedy personal self, which can be mobile and exposed to risks of accidental loss or damage. By contrast, a server platform provides protection, fixed, and managed environment for shared resources.
Figure 3 server platforms many to choose
Even when the same technology used for the client and server platforms (eg PCs with the same type of hardware and operating system) these distinctions between personal and shared resources must be done. In the limit, the same machine can be a personal platform and a server platform (eg a peer-to-peer, see 3.2). As always, the obligations arising server role to ensure the availability and integrity of shared resources.
client-server middleware: -
We define client-server middleware as:
Software package to support the separate parts of the application server-client software and can work together. This is by far the more complex area of client-server technology. By concentrating the complexity here we can keep the other areas relatively simple. Includes many types of functions, each of which can be distributed, and most of which are interrelated. Some of the main areas are:
• Network services
• Distributed Application Services
• Distributed systems management
• Distributed security
• Distributed object management
• User Management Interface
• Print management
• Data management
• Transaction Management
• Workflow Management Figure 4 is a symbolic representation of middleware applications that support client-server software. It emphasizes the importance of middleware to enable the client-server technology to work across the entire business area relevant to user tasks. This may involve interaction across departmental and functional boundaries, and perhaps through the company's borders.
Figure 4 client-server middleware
The client-server tools and services: - The client-server systems can be complex, but well-integrated systems, well-designed user interfaces technical complexity should not be visible to the user, is essentially a problem for the application developer and service provider. They need development tools software and professional services to help manage and hide this complexity. Many of the tools and services needed are the usual suspects, but there needs specific client and server systems. An important general point is that for packaging (shrink-wrapped ") software application, the user enterprise tool-building program. Consumer Packaged Goods client-server application are becoming widely available (eg, distributed office and groupware applications, representing business applications, personal and payroll). Another important trend is that different tools (and languages) are required for different parts of modular application systems. The main distinctions are:
• User Interface: languages and tools for building graphical user interfaces and any application logic associated with them closely, for example GUI tools and Visual Basic.
• Base Data: languages and tools for the construction of databases, file systems and object stores, and building the application logic closely associated with them, such as data manipulation languages and 4GL relational database.
• Business logic: languages and tools for building application logic is logically independent of user interfaces and databases, such as COBOL.
• Distributed processing: languages and tools specialized for distributed processing, and covering all functional areas above (and other technological and organizational boundaries), eg Remote Procedure Call (RPC) tools.
• System management: methods and tools for electronic software distribution, operation and optimization of client-server systems.
Most of these tools are associated with the corresponding areas of middleware.
Chapter-6
Client-Server Architecture: - Looking back on the technology described in the previous section, there are three types of client-server architecture can be discerned.
based client-server: - In client-server architecture based, personal or centralized application is divided into two parts: a client into a personal platform, and part server in a server platform. The latter is usually a shared resource, as a service for production of a print service, a database, or some function application-specific. The terms client and server is used to refer to the hardware platforms and application software components (often somewhat ambiguously). Basic client-server architecture is illustrated in Figure 9 (and has been shown in more detail in Figure 6).
Figure 9 Basic-Client-server Architecture of client-server configurations are usually organized around a local area network (LAN). The set is usually described as a PC-LAN, and consists of many PCs for personal use (personal platforms), plus one or more PCs sharing (server platforms). The local server platforms such as PC-LAN general are portals across the enterprise and external networks, and servers from them. This is illustrated in Figure 10.
Figure 10 A typical PC-LAN Although primarily result in terms of PCs and PC LANs, these basic concepts of client-server are applicable to all types of computers and networks (eg, PC, UNIX, mainframes, networks LAN and WAN).
Beyond the basics: - Beyond the basic client-server is not peer-to-peer processing, co-operative processing and treatment independent. The peer-to-peer processing a term used to refer to settings in which there is no server platforms and server parts of applications are staff on the platforms. Networks operating in this database, known as "peer-to-peer networks. This is a low cost way of implementing small PC-LAN, etc. but the lack of separate server platforms diminishes the integrity of the system and gives rise to difficulties in managing the system. The term processing is used Cooperation to refer to the settings in which application software distributed on separate server platforms, and the client and server ends of interactions are both in server platforms. This includes the interaction between individual applications, not only between the parties to the same application. The term independent processing is used to refer to configurations in which all parts of an application are in a platform (usually a personal platform.) Any relationship client-server between the parties are not visible externally. People also use the terms "peer-to-peer cooperation and processing interchangeably, and several other meanings. This causes confusion and misunderstanding. There are also several other lesser-known formulas as a server / applicant and the producer / consumer. All main formulations are illustrated together in Figure 11.
Figure 11 different formulations of system server-client structure Unfortunately, many people strongly differentiate the concepts of other client-server (so they really mean basic client-server). This obscures the vital point that all are variants within a structure Unified: client-server architecture. It also leads to misleading claims in the sense that the client-server (meaning core client-server) is idle, and is being replaced by other techniques such as cooperative processing.
General client-server architecture: - A fundamental limitation of the base client-server and all formulations at 3.1 and 3.2 is to define a software configuration depends on the hardware configuration. In addition, it is often ambiguous if the terms client and server refer to the hardware or software. To escape these limitations and ambiguities, server-client relationship must be defined software independently of the software localization, and irrespective of any classification of the underlying hardware as clients or servers. The clarification is essential that client and server are roles that are used and services provided (respectively), and these functions are in a relationship between the building blocks independently. In this regard, one participant uses a service (has the role of client) and another providing the service (it has the server role). This is a client-server relationship. large and flexible configurations can be constructed by combining these simple concepts. This is illustrated in Figure 12.
Figure 12 The principles of architecture client-server as shown on the right side of the diagram, a building block can be both user and service provider. Therefore, the client may have functions server and can participate in many client-server relationships with building blocks. Client or the server is only in the context of the specific relationship under analysis. The implementation of client server software architecture is through programming languages and middleware (not shown in Figure 12). The physical realization of client-server architecture consists of separate computer networks, hence the term client / server tends to become synonymous with distributed processing. client-server architecture is only incidentally about computers, or use of any particular type of technology. However, in the present circumstances is usually desirable for the client-server is seen primarily in terms of exploitation of the technology of PC (as defined by Gartner started in point 1.2 above). This general form of client-server architecture (autonomous building blocks, client-server relationships, the role of client, the function server) is a key ingredient of the open application architecture framework.
Assumptions: -
1.A client is connected to a maximum of one server at a time. [The client later refuted this hypothesis.]
2.Replication is a side effect of the rich client's existing architecture, we assume that updates one server are automatically propagated in a timely manner.
3.A single client can have more than one session. [Replaced Assumption 1.]
4.All calculated columns (Columns that represent the behavior rather than issues) is calculated easily and quickly on the server.
5.Deletion or insertion of a row requires an update window on the client.
6.Transmission client-server traffic is out of range.
Chapter-7
Architecture Types: - When considering a measure for client / server computer, either to replace existing systems or introduce entirely new systems, professionals must determine what type of architecture intend to use. The vast majority of end-user applications consist of three components: presentation, treatment, and data. The client / server architectures can be defined by how these components are divided between the software entities and distributed on a network. There are a variety of ways to divide these resources and implementing client / server architectures. This paper will focus on the most popular application of two levels and three levels, client / server computing systems. Two-tier architecture: - Although there are several ways to design a two-layer client / server system, we will focus on examining what the application is overwhelmingly more common. In this implementation, the three components of an application (submission, processing and data) are divided between two software entities (Levels): client application code and database server (Figure 2). A robust client application development language and a flexible mechanism for transmission of client requests to the server is critical for successful on two levels. Presentation is handled exclusively by the client, the processing is divided the client and server, and data are stored and accessed through the server. The PC client assumes the bulk of the responsibility of the application (functionality) logic regarding the treatment of components, while the database engine - with its attendant integrity check, the query capabilities and functions of central repository - Manage data-intensive tasks. In a data access topology, a data engine to process the requests sent by clients. At present, the language used in these applications is typically a form of SQL. The SQL sent from client to server requires a close linkage between the two layers. To send the SQL client should know the syntax of the server or this is translated through an API (Application Program Interface). You must also know the location of the server, how organized data, and how the data is called. The application logic may use the stored and processed on the server, which will centralize global tasks such as validation, data integrity and security. The data is returned to the client can be handled at the client level to select further sub, business modeling, "what if" analysis, information, etc.
Figure 2 - Access to data topology two-tier architecture. Most of the functional logic exists in the level Client The most attractive advantage of a two-tier environment is the speed of application development. In most cases a two-tier system may develop A small fraction of the time it would take a legacy system code comparable but less flexible. Using any of a growing number of tools based PC, a developer can single data model and populate a database on a remote server, paint a user interface, create a client application logic, and include data access routines. Most two-level tools are also extremely robust. These environments support a variety of data structures, including a number of built in procedures and functions, and isolate the developers from many of the more mundane aspects of programming and memory management. Finally, these tools also lend themselves well to iterative prototyping and rapid application development (RAD) techniques that can be used to ensure that the requirements of Users are accurately and completely satisfied. Tools for developing two-tier client / server systems have enabled many organizations is to attack their pending applications, user satisfaction contained up demand for the rapid development and deployment of solutions which are mainly smaller group based work. two-tier architectures work well in relatively homogeneous environments with relatively stable business rules. This architecture is less suitable for scattered heterogeneous environments with rapidly changing standards. organizations, as such, relatively few customers with two levels / server architectures providing cross-border service platform solutions business across departmental or cross Given that the bulk of application logic exists on the client PC, architecture Level two faces a number of version control and possible implementation problems of redistribution. A change in business rules that require a change in logic client in each application in the portfolio of a corporation, which is affected by the change. Amended customers would have to be re-distributed through the network - A potential difficult task, given the current lack of robust control software version of PC and problems related to the improvement of the teams are off or not "docked" to the network. Security system in the two-tier environment can be tricky because a user may require a different password for each SQL server access. The proliferation Query tools end users can also compromise the security of database server. The vast majority of client / server applications developed today are designed without sophisticated middleware technologies, which offer greater security. Instead, end users are provided a password, which gives access to a database. In many cases the same password can be used to access the database with data access tools available in most spreadsheet PC business and database packages. The use of such a tool, a user may be able to access otherwise or possibly tables and fields of data. Customer corrupt tools hidden and software environments used in SQL through two levels are also very own instruments PC market is extremely volatile. The client / server marketing tool seems to be changing at a pace more and more unstable. In 1994, the leading client / server tools developer was bought by a company large database, increasing concern about the ability of the manufacturer to continue working with RDBMS providers that compete with products from the parent company. The number two tool-maker lost millions and has been labeled as a takeover target. A company also in the midst of severe financial difficulties and transition management supply of the tool, which has received some of the brightest praise in early 1995. This kind of volatility raises questions about the long-term viability of any proprietary tool an organization can undertake. All this complicates the implementation of systems of two levels - a proprietary technology migration to another, require the company to scrap most of their investment in application code, as none of this code is portable from one tool to another.
Three: - The most sophisticated level Web-based applications that involve data entry, are based on a client-server architecture of three levels. The three levels are
• The client (web browser)
• The web server / application server
• The database server architecture level of the tree (Figure 3) attempts to overcome some of the limitations of two-tier system, separating the presentation, processing, and data into separate entities other software (levels). The same types of tools can be used for presentation as used in a two-tier environment, however, these tools are now dedicated to handling only presentation. When the client requires the filing calculations or data access, making a call to a server for mid-level functionality. This level can perform calculations or make requests as a client for additional servers. The mid-level servers are usually encoded in a highly portable language, not private, and functionality C. Servers The arches can be multi-threaded and can be accessed by multiple clients, including separate applications. Although three-tier systems can be implemented using a variety of technologies, customer call mechanism to the server in the system, as is more typical of the remote procedure call or RPC. Since most implementations of SQL involve two levels of messaging and most three-tier systems use RPC, it is reasonable to consider the merits of these respective application and response mechanisms in a debate on architecture. RPC calls from client to server middle-tier presentation provide greater flexibility of the system in general SQL calls made by customers in the two-tier architecture. This is because in an RPC, the client requesting it simply passes the necessary parameters for the application and provides a data structure to accept the return values (if any). Unlike most two-level implementations, the client's presentation of three levels not is obliged to "speak" SQL. As such, the organization, names, or even the overall structure of the back-end data can be changed without requiring changes presentation to the PC-based clients. Since SQL is no longer necessary, the data can be organized in a hierarchical, relational, or object format. This flexibility can allowing a company to access legacy data and simplifies the introduction of new database technologies.
Figure 3 - Architecture of three levels. Functionality most servers handle the processing logic. The arches can access the code and used by multiple clients In addition to opening stated above, several other advantages are provided by this architecture. Having separate software entities may allow parallel development of the individual levels of specialists applications. Note that the skill set needed to develop c / s applications differ significantly from those needed to develop systems of character based on mainframe. As examples, the creation of the user interface requires an appreciation for the platform and corporate standards for user interface design and database requires a commitment and understanding of data model of the company. Having experts focus on each of these three layers can increase the overall quality of the application final. three-tier architecture also provides a more flexible allocation of resources. server functionality arches are very portable and can be allocated on a and changed dynamically as the organization's needs change. Network traffic can potentially reduce the functionality of server data strip to the structure exact required prior to distribution to individual customers LAN level. Multiple applications servers and access to complex data may originate from the intermediate layer instead of the client, further decreasing traffic. Furthermore, as PC clients are now dedicated to only display, memory and disk storage requirements for computers potentially be reduced. modular code modules designed middle level can be reused by many applications. reusable logic can reduce subsequent development efforts, minimize the maintenance workload and reduce the costs of migration to changing client applications. In addition, platforms implementation of three-level systems such as OSF / DCE offer a variety of additional features to support the development of distributed applications. This includes security integrated directory and name services, server monitoring and the ability to boot to support dynamic fault tolerance, and distributed time management synchronization systems across networks and different time zones. Of course there are drawbacks associated with a three-tier architecture. Current tools are relatively immature and require more complex 3GLs average generation level server. Many tools have been developed in the facilities maintenance server collections - a potential obstacle to simplify maintenance and promotion of code reuse through a is organization. More code more sites also increases the probability that a system failure will affect a planning application in detail, with emphasis on the reduction or elimination critical path is crucial. Three levels brings a greater need for network traffic management, server load balancing and fault tolerance. To technically IS organizations strong customer service with rapidly changing environments, three architectures can provide significant long-term benefits through increased responsiveness to changing business climate, code reuse, maintenance, and ease of migration to new server platforms and development environments.
Comparing two and three activists tire development: - The graphs in Figures 4-6 illustrate the implementation time of two levels in front of three environments level. Implementation time of the day is forecast for delivery of systems, not man-hours. A study by Deloitte & Touche, faster development time application is cited as one of the main reasons companies chose to migrate to client / server architecture. As such planning decisions and the strategic platform requires an understanding of how the development time for architecture and how changes in development time as one of IS gain experience in c / s.
Figure 4 - Initial development effort Figure 4 shows the initial development effort intended to create comparable distributed applications using the common two-level, three approaches levels discussed above. The three-tier application takes much longer to develop - this is mainly due to the complexity involved in coding the bulk of the application logic in a lower 3GL such as C and the difficulties associated with the coordination of multiple independent software modules on platforms different. By contrast, the two-tier system allows most of the logic of the application to develop a high level language within the same tool used to create the user interface.
Figure 5 - Development posterior development efforts subsequent efforts can see three levels deployed applications faster, two-level systems (Figure 5). This is entirely due to the amount of mid-level code that can be reused from previous applications. The speed advantage favoring the three-tier architecture will only result if the three-tier application can use a considerable part of the existing logic. Experience indicates These savings can be significant, especially in organizations that require separate but related applications close for several business units. Reuse is also high for organizations with a strong company data model as the data access code can be written once and used again whenever the need similar access arise in many applications. The degree of reduction of development time on subsequent efforts to grow as an organization deploys more c / s applications and developed a substantial collection of re-usable application logic to be average.
Figure 6 - Migration Tool customers can be found 6 presents the major arguments for saving code when migrating from a client development tool to another. It said earlier that the client tools are themselves and code is not portable between packages of major brands. It was also noted that the PC market is very volatile tools with the vendor and technical shakeouts "Leapfrogging" commonplace. In a two-tier environment, IS organizations wishing to move from a development platform based on client PC to another will have scrapped its previous investment in the application logic because most of this logic is written in the language of the tool itself. In the three-tier environment this logic is written in a medium-level reusable, therefore, when migration to the new tool, the developer only has to create the presentation and add RPC calls to the layer of functionality. Flexibility in the reuse of existing mid-level code can also help organizations to develop applications the client PC of different OS platforms. Until recently there were very few customers cross-platform development environments and tools to most of today cross-platform solutions are not considered "best in class." In an environment of three different levels of client tools can access platform-independent functionality of the middle layer level. Coding application logic once in a medium accessible reduces overall development time in the cross-platform solution and provides the organization more flexibility to choose the best tool on any platform.
The characteristics of the client / server architecture: -
The basic characteristics of client / server architectures are:
1) The combination of a client or a part of front-end that interacts with the user, and a back-end server or portion that interacts with the shared resource. The client process contains the logic of specific solutions provides the interface between the user and the rest of the application system. The server process acts as a software engine that manages shared resources such as databases data, printers, modems, or high-power transformers.
2) The task of the front-end and back-end tasks have different requirements resource implications computer, such as processor speed, memory, disk speeds and capacities, and input / output.
3) The atmosphere is often heterogeneous and MultiFinder. The hardware platform and operating system of the client and the server is often not the same. Client and server processes communicate through a well defined standard programming interfaces (APIs) and the PRC.
4) An important feature of client-server systems is scalability. It can be scaled horizontally or vertically. Horizontal scaling means adding or removing client workstations with only a slightly higher performance impact. Vertical Enlargement means migration to a server computer bigger and faster or multiservers.
Client-server applications: -
We define an application client-server as:
An application system in which, logically, independent software components are integrated together through client-server relationships.
In a client-server relationship, a part of an application (the end user) uses a service provided by the other (server side). The latter is usually a shared resource used by many customers. Although it built through the client-server relationship, the parties remain separate. We refer to them as naturally different, since need not be physically distant from each other (perhaps on your computer). We describe the implementation of client-server software here, in three steps: the division of an application, joining the separate applications to it, and distributed the same application structure
The division for an application: -
Figure 5 modular application software There are many ways of partitioning software into separate components. However, the content most applications usually fall into three categories with different techniques: data management, application logic and presentation. This illustrated in Figure 5. If the application is divided into two parts (one part in a client platform and the other on a server platform), the division can be made in any of the two boundaries between the functions, or within one of the three functions. Consequently, there are five main ways of dividing a centralized or personal application into two parts between which there is a client-server relationship. This is the basis for classification in five styles popular client-server, which is promoted by the Gartner Group. Illustrated in Figure 6.
Figure 6 Five styles of the basic structure generic client-server
The details do not concern us here. The important point is that suit different different styles, needs and circumstances:
• The two styles to the left of the diagram are typical of a centralized interactive applications that have adapted client-server through the graphical interface technology, terminal emulation, etc.
• The style in the center of the diagram is typical object-oriented distributed applications and distributed TP applications where the data is encapsulated and function together after application interfaces
• The two styles to the right of the diagram are typical of the data focused on client-server applications using 4GL development tools and relational products Some database applications to combine the three areas of function (presentation, application logic and data management) in the personnel platform. In addition, different styles may occur alternately on the same platform.
Join applications together - one of the great strengths of client-server is the ability to join together separate applications. This can be done in many ways, but the principles used in 2.4.1, there are essentially three levels in which applications can interact with each other. This is illustrated in Figure 7.
Figure 7 Three levels at which applications can be joined
The main characteristics and advantages and disadvantages of these three approaches are:
• A presentation layer: Interaction at this level is achieved through exchange Data Direct (DDE) within a window management system, or through scripts, see Duxbury [1994], which uses software from a user interface application by simulating a human user. This type of technique is often referred to as screen scraping. It is very useful for accessing legacy applications but leads to software maintenance problems if the user interface needs to change.
• Depending on the level of implementation: The interaction in this level is in terms of business functions. Therefore, applications are applications among business about the meanings of the application (and not its presentation or database coding). This has the advantage of maintaining their internal designs separated from their external interactions. There are fewer problems with software maintenance.
• A level Data Management: The interaction at this level is, with direct access to the other database application. This is a common practice, but leads to problems software maintenance data with an application to change the structures.
The first and third approaches inhibit the possibility of change, the second not. distinctions can be made between direct and indirect interaction between applications, synchronous and asynchronous interaction, and externally programmed interaction and interaction programmed internally.
Structure of the distributed application: - Distributed applications are evolving towards networked structures such richly illustrated in Figure 8. The circles represent individual software components, and the lines represent the client-server relationships between them. This is typical of the kind of structure resulting from the use of object-oriented design and distributed object management.
Figure 8 Distributed Applications compound is also found in large-scale structure systems of distributed applications (in which individual relationships occur client-server). Generally, three levels of application software can be discerned in large-scale structure:
• Front levels: the application software (and databases) for personnel platforms, providing all the services and applications, using local resources and remote resources. In general, platforms are PC. This level is where the greatest amount of computing power and development of computer applications is unfolding.
• Middle level: The application software (and databases) in server platforms, providing the back-end personal applications, Workgroup shared services and service-oriented tasks. Typically, the platforms are UNIX or PC. This level provides a quick adaptation to change business process, without changes in the level back. It puts boundaries around the turbulence and uncertainty generated in the volatile world in the first level where all users are. It also provides links across the enterprise side (eg, email services).
• Return levels: software Application and database server platform providing corporate information services. These tend to be functionally partitions (for example, accounts, production, staff). Typically, the platforms are mainframes. This level provides the core of shared information assets and long life that everything else depends. There strong guarantees on the integrity of data and applications and databases are stable, and design changes rather slowly.
This structure separates the different types of concerns, once together in centralized computing
Chapter-8
Important Client Server: -
Benefits Client-server: -
Low cost ØPotential
ØImproved performance
ØIncreased security
Omora GUI Application
People warheads the opportunity to make a change for the better
ØBetter SW development tools once established
ØExploits existing H / W, S / W configurations
ØMatches distributed business models
Oscal
ØFlexibility and cost savings
ØFlexibility business models
technology choice component ØMaximum
ØEfficient use of computer resources
Odate interoperatability interchangeability and
ØEnhanced data exchange
ØIntegrated services
ØSharing platform resources between devices
ØLocation data independence and the process of
ØTechnology revolution
ØFuture technology
ØRelational databases
ØDisadvantages client-server: -
Upfront cost ØHeavy
ØInitial performance decrease
ØLack qualified professionals
ØNeed to rewrite a lot of software
ØNeed user Recycling
ØDependability, when the server falls, where operating
ØLack mature tools
ØLack scalability of the network operating system (for example, the novel by NetWare, Windows Server NT) are not very scalable
ØHigher than expected costs
ØHarder to build
Stable ØLess
ØSusceptible network load
ØLacking specialists in
ØDifficult to debug
ØDifficult to test
Client / Server Business Application Architectures:
application architectures their traditional function based on today to meet the needs of the enterprise application architecture should reflect the full range of business requirements.
Therefore, the client / server computing requires a view of three layers
organization.
1 The user interface layer, which implements the model functional
2 The business function layer, which develops the process model
3 The data layer, which implements the information model should be noted that this application architecture does not require multiple hardware platforms, although the technology can be used, if the environment is sufficiently robust and reliable and company is willing to pay the additional costs associated with workstation and LAN technology.
Business Benefits: - There is a perceived need for independence the seller. This includes application development methodologies, programming paradigms, products and architectures. - Organization have changed from steep hierarchies to flat hierarchies - Network management is replacing vertical management - There is a change based management team - The client must have a single point of contact for all business with the organization - the customer is faced with the same person over multiple contacts. - The user will perform the processing as possible during the time contact with the customer - The time needed to complete the work will be minimized - There is a need for staff training and audit trail of actions - Multi-skilled and multi-function teams need access to multiple applications
Different types of servers: -
The easiest way servers are disk servers and file servers. With a file server, the client passes requests for files or records of more than a network file server. This form data service requires high bandwidth and can slow a network with many users significantly. Traditional LAN computing allows users to share resources such as data files and peripheral devices, moving independently of UCP a file server (NFS). The more advanced form of servers are networked database servers, transaction servers and application servers (Orfali and Harkey, 1992). In database servers, customers move from SQL (Structured Query Language) as messages on the server and the results of the query is returned by the network. The code that processes the SQL application and data reside on the server that allows use its processing power to find the requested data, instead of passing all the records and allow a customer to find their own
Data as was the case File Server. In transaction servers, clients invoke remote procedures that reside on servers, which also contain a database engine of SQL. There are statements procedure on the server to run a group of SQL statements (transactions) which either all succeed or fail as a unit. The server-based applications transactions are called on-line Transaction Processing (OLTP) and tend to be mission-critical applications that require response time of 3.1 seconds, 100% of time and require tight controls over the security and integrity of the database. The communication overhead in this approach is kept to a minimum as the exchange typically consists in a single request / response (as opposed to multiple SQL statements in database servers). The application server databases are not necessarily centered but are used to server user needs, such as.
Download the capabilities of Dow Jones or regulating a electronic mail process. Base resources on a server allows users to share data, while security and management services, which are also based on the server, ensure data integrity and security.
Special types of architecture:
IBM System Application Architecture: AEA is a collection of selected software interfaces, conventions and protocols that are used as a framework for the development of compatible applications, integrated through IBM mainframe environments.
Four main components of this architecture are: - Common User Access (CUA) defines conventions for GUI appearance. - Common Programming Interface (CPI) provides languages, tools, APIs and applications that offer greater portability and more consistent user interfaces across multiple platforms. - Support joint communication (CCS) is compatible with existing communications standards, such as LU 6.2. - Typical applications written by IBM, will serve as demonstrations of SAA concepts and facilitate users migrate between systems.
APPLE Architecture is vital - VITAL provides a way of building information systems constructed from generalized About the Author
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