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Network Architecture Introduction Tier" can be defined as "one of two or more rows, levels, or ranks arranged one above another" (1) ). So from this, we get an adapted definition of the understanding of what N-tier means and how it relates to our application architecture: "Any number of levels arranged above another, each serving distinct and separate tasks." To gain a better understanding of what is meant, let's take a look at a typical N-tier mode N-Tier is a very broad term, it can mean a lot of things. Below are some examples of n-tier implementation: a computer application containing any number of tiers or logical layers, using a reusable, component based approach. This software type is characterized by flexibility and scalability: it can operate in multiple configurations, using any number of physical systems. These features are vital for dynamic business environment. a strategy for bringing a miscellaneous collection hardware into a unified system.
N-Tier systems may utilize a wide variety of computer languages, operating systems, and platforms. a framework for creating a adaptable, distributed computing environment, that can take full advantage of the infrastructure and resources you currently have, while preparing for whatever changes the future brings. a variation on the traditional Client / Server architecture, which uses Internet/intranet related technology, to make the most of existing skill and equipment, at the same time preparing a reliable, flexible framework for change and growth. a method for centralizing control over increasingly critical information, while while allowing greater freedom for inner-departmental innovations and encouraging input from customers and suppliers The Basics of N-Tier Network Architecture It all started with solitary computers that were accessed by users though terminals. This was a single-tier architecture the programs and data was used only on one machine. The wide-spread popularity of desktop computer has lead to two-tier architecture or client-server systems; workstations has split some work with back-end servers, usually by running the program and leaving servers to carry on with more general and important tasks like company databases.
This differentiation in function worked quite well and was perceived as positive. However, extensive use of the client-server architecture has revealed some inborn limitations. First, roll out and upgrade ordeals client software must be installed and managed on a potentially large number of separate, diverse clients across the entire network. Software installations, updates or replaces can unreasonably costly in terms of money, efforts and downtime. Furthermore, server failures and consequent downtime have become characteristic feature of client-server architecture. Consequently, three-tier systems has been developed to address some of the issues pertinent to client-server architecture . Actually, there are a number of reasons for adding another layer, and two of them are thin clients and distributed processing. In a typical three-tier architecture, the first layer still handles the database or other centralized data stores; the second layer is where specialized application servers running the programs and/or business logic is run; and the third layer is the client.
In the thin client model, the client part is nothing more than the user interface (UI). Here, the client layer is precisely thin; there is not much to maintain, because the business logic is implemented in another layer, typically with the help of some form of middleware product, such as an application server. Actually, if a Web browser employed as a client UI, it can greatly reduce the need to program a custom client , making the applications accessible to a wide range of client types and platforms. Moreover, hardware demands on client part is reduced as well, anything that can run a Web browser is suitable, including PCs, Macs, Network Computers, Unix workstations and Javastations. This boosts portability across platforms, and also allows organizations to better utilize older computers even with most recent state-of-the-art enterprise applications. In addition to the above-mentioned advantages, middle-tier solution confines development, deployment and maintenance of most of the code to a limited number of dedicated application servers, which is much easier compared to serving multitude of desktops.
In a properly implemented three-tier system back-end and middle-tier services can handle the details of data replication and synchronization and automatic load-balancing, providing redundant number of client UI and database copies to cover shortages in case of a component failure. This makes the system more failure-proof, stable and reliable for the end user. Basics of N-tier Application architecture Since no n-tier approach is possible without corresponding application architecture, it is essential to know the basic of n-tier application architecture. As can be seen in the picture below, typical n-tier architecture has 5 layers or tiers: data layer, data access layer, business layer, presentation logic layer and presentation tier. Data layer described above is an important part. Although theoretically the system can work without this tier, most system will require this part. This where Database Management System (DBMS), like SQL Server, Access, Oracle, MySql reside. This layer is solely aimed to deal with the storage and retrieval of information. It doesn't care about how you plan on manipulating or delivering this data.
Data access layer accommodates interfaces for data access. These can be generic like method for creating and opening a Connection object as well as specific ones like "saveProduct". This layer is only a reusable interface to the database. Business tier is the brain of your application; it includes things like the business rules, data manipulation, etc. For example, if you're developing a search engine and you put rate/weight each matching item based on some custom criteria (say a quality rating and number of times a keyword was found in the result), place this logic at this layer. When creating this layer, a developer should not be concerned with code or databases, but only with business logic of the application.
At presentation tier the system meets its end user. The interface should provide the user with meaningful output, it can include standard ASP documents and Windows forms. Below is the drawing of a typical n-tier application architecture. References: Robert Chartier. Application Architecture: An N-Tier Approach - Part 1 October 21, 1999 November 27, 2002 http://www.internet.com/icom_cgi/print/print.cgi?u rl=file:///E:/Documents%20and%20Settings/Administr ator/Desktop/N-tier/An%20N-Tier%20Approach%20-%20P art%201.mht N-tier.com N-Tier -- The Future of Computing November 21, 1999 November 27, 2002 http://www.n-tier.com/future_print.html#nbc N-tier.com N-Tier vs. 2-Tier July 21, 2000 November 26, 2002 http://www.ilt.com/AEDIS/Ntier/ The thin.net Thin client technology overview July 21, 2000 November 26, 2002 http://thethin.net/whitepapers/PRESENTATIONS/ThinC lientPaper.htm 5. Bruce Robertson Middleware: MOM's Not the Word October 2, 2000 November 27 http://www.networkcomputing.com/1119/1119f1guestco l_1.html N-tier implementation N-Tier implementation means using whatever mix of Computer Hardware and/or Software Layers you need, in order to achieve desired results.
N-tier architecture can be compared to a Lego constructor set any number of component-based clients, interfaces, agents, transactions, middleware and data servers flexibly can be connected to get a desired network. Like in Lego, all building block are modular and independent. That is the beauty of n-tier. The rapid move to the N-Tier network computing model, indicates a powerful computing trend and is currently having a huge impact on both Enterprise and Web-based applications. These systems are also called as: thin-client, browser-based, network-centric or multi-tiered computing, N-Tier computing encapsulates all of these concepts, which in turn sprout in infinite number of network configurations matching almost any business situation. Despite the overall and rather steep decline in IT budgets of most business that can be attributed to poor economic climate, N-tier solutions has shown a steady growth.
Companies are somewhat reluctant to invest in completely new and unproven technologies, but N-tier or solutions gained wide-spread acceptation; they allow companies to make most of their investment. Nearly two thirds of respondents in research conducted by Giga Information Group have already deployed n-tier technology in one or another way. Although only 32 percent believe it is strategic technology, almost all of the surveyed see short-term return on investment (ROI). The upcoming years will introduce more of Web Services and Web portal elements into n-tier architecture. Some systems that once employed thin client as an isolated operating environment, will be integrated with Web Services. Due mainly to the financial benefits that brings n-tier architecture, Giga expects the market to grow by 10 percent to 20 percent annually through 2004 to as much as $2.4 billion.
If n-tier technology, particularly middle-ware solution, was initially realized as a primary workgroup and remote access solution, now it is making its way right into large enterprise deployments. Citrix, which is a leading vendor in SBC product niche, has enjoyed fast growth: if in 1999 it installed 300 seats than in 2000 they supplied approximately 1000 seats. Application integration and re-engineering software market is hard to imagine without n-tier technology. According to Framingham, Mass.-based market research firm, this niche will reach around $10 billion by 2004. A good example of a growing company in this sector is Relativity Technologies, the company's strategy is to adapt legacy applications to n-tier and e-business architectures, rather than just inventorying the older Cobol, PL/I, and Natural Adabas programs, says Len Erlikh, CTO of Relativity, in Research Triangle Park, N.C. He also stressed that the key is seeing business rules and making the components reflect these rules.
The companys RescueWare 6.0, a package for automating the transformation of legacy business assets to modern e-business architectures aimed to do exactly that. The tool helps to alter original systems' rules and workflow to meet the design goals of the newer applications. A number of companies choose services similar to Relativitys to rewrite existing code rather than create new for economical considerations, said Dana Gardner, an analyst at Aberdeen Group, in Boston. For example, National City, a Cleveland-based bank holding company encountered problems with its client server application that was internally developed. The software was difficult to support, besides it had Y2k problems. Jim Hughes, CIO, said "We had to keep the application but didn't want to pay for a rewrite." The company opted for Rescue Ware, Relativitys software, which helped to convert the application to provide thin client interface, so that back-end data can be accessed trough browser interface. Flexibility of n-tier architecture helped National City to save around $3 million had the company decided to purchase a application.
The above are only few examples of successful employment of n-tier architecture. The fact that around eighty percent of 1000 Fortune companies have adopted n-tier architecture speaks for himself. Yet, with the growing popularity of hand-held computing devices, n-tier or thin client architecture is going to get a new momentum. Mobile N-tier Mobile devices is something IT industry is buzzing about; this small computers are inexpensive allow access to critical data in increasingly mobile business world, allowing companies be closer to the customer. This means better service, more efficient resource management and consequently competitive advantage on the market place. N-tier architecture has great potential delivering business data and processes in the real of mobile computing. Today's n-tier architectures usually incorporates a business object layer based on a distributed object technology like Common Object Request Broker Architecture (CORBA), Distributed Common Object Model (DCOM), or Enterprise JavaBeans (EJB). Mobile computing has its own requirements on middle ware solutions that are most popular n-tier formular today.
Mobiles require small-footprint applications that can access business objects deployed in existing middleware servers. The most common answer to this need is a copy and sync architecture. Data copied to and received from the PDA application is later synched with the main system by a serial connection and proprietary synching software. Obviously, this system has serious flaws: the applications tend to be bulky and resource demanding, data consistency is unsatisfactory due to multiply users making changes offline. Moreover, live access to critical data is denied, limiting key benefits of mobile computing. There is a growing need for a lightweight, easy-to-implement architecture that allows smooth access to distributed objects from an Internet-enabled PDA.
Developing applications for mobile platforms, like PDA, clearly put unique requirements. Such a device usually has 1-4MB of memory, so minimizing hardware requirements for such application is critical. Low-bandwidth is still a sad reality for many places and situations, so firewall security can mean no access at all. In addition, the toolkits for developing PDA applications are scarce, even without considering access to EJBs or CORBA. Once typical practice was usage of a socket connection, but as security concerns grow, systems administrators are reluctant to provide that type of connection. In addition to the above-mentioned narrow points, PDA has no inherent security, so developers must take this into account since no mobile device will ever be popular if it a potential vital information leakage.
Also it should not be forgotten many proprietary data transfer formats that should be brought to a unified one, otherwise application development for such devices will be greatly obscured. Once the above-mentioned bottlenecks eliminated, mobile and distributed computing will create a powerful wireless networks, Wireless Application Framework (WAF) is concept currently being developed should bring an array of applications, interaction protocols into a unified system , .Main components of mobile distributed system will be different platform PDA and other mobile devices, communicating with distributed server environment. Although the main task of WAF will be used to instigate online processing, the main goal of WAF is to provide framework for creating loosely connected and asynchronous distributed systems. Data consistency and integrity will be achieved through periodic asynchronous data exchange between WAF server environment and mobile devices. The history clearly shows that the future of computing is not with a desktop computer as we know it today, it will be with a network computer and Internet. The popularity of the Web has urged creation of "Browser/Network Computing" and n-tier architecture perfectly fits this vision providing necessary means to create upcoming flexible, readily available networks. N-Tier architectures are truly Net-Centric, these technologies quickly become indispensable for enterprise application development and companies around the world are adopting it in order to get ahead in the emerging net economy. N-tier technology will empower and popularize a great variety of network-based devices, such as Internet Browsers, Web-TV, Smart-Phones, Personal Digital Assistants (PDA's), to meet the need of businesses and individuals alike. References Brad Williamson Thin Client Technology July 2001 November 26, 2002 http://thethin.net/whitepapers/PRESENTATIONS/ThinC lientPaper.htm Erika Morphy Siebel Adds Mobile CRM to the MixMarch 15, 2002 November 26, 2002 http://www.crmdaily.com/perl/story/16795.html Daniel Mrep Extended Systems Releases Middleware Application Server October, 2001 November 26, 2002 http://www.extendedsystems.com/ESI/Company+Info/Ne ws+-+Events/ John Allen Merging Mobility and Middleware May, 2001 November 26 http://www.inquiry.com/techtips/xml_pro/ 5 Sean Sorceback Wireless Application Framework (WAF) April, 2001 November 26http://www.rim.com/.
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