Chapiter 7: IT project management in the client/server environment.
Evoluation of a noun.
Are IT projects easier or more difficult to than other kinds of projects? In the first place, that depends on your realization of a development in the frame or in manner of a frame. In another terms, is your client/server system your environment of development or a cible environment?
In the second place, does your project function well with this type of environment repartition or is it imposed by the circumstances(in another terms, do you have the choice?)we will all agree explain how and why this forme of architecture repartition is evaluated.
Someones of the big computer of 20 years ago have easily to be red in front of the personal computer today. The gigant chronologic series of CDC6000 or IBM 370 have the bad to compete with numbers of characteristics of a PC 486 66 MHz, not speaking about Pentium Intel or of the power PC of Motorola.
One of the first faults of the gross computer became the mini computer like PDP and the VAX of the digital equipment. The mini computer are competitive to the technic and economic level, but in term of the performance, they can’t compare to the strong cousins. The lack of power of the small computers are firstlq evident in these 2 areas: that of calculation and that oF number of users. The computers became mobe smaller, cheaper and multivalued, the idea of their connection between them began to take the form. DEC got these grappes, IBM their networks and in all phe ID industry, the competition between partisans of repartition treatment and centralized treatment partisans. When the smoke disappeared, the partisans of repartition computer connected by the networks became the lead.
The repartition of the calculation power is in the origin of the evolution into the client/server system. For the chief of IT project, that pose one new kind of defi. When the repartition system place one computer in each service, client/server system in place one on each office.
The client/server concept places the calculation power between the mains of the final users, in their allowing of choosing their own computer terminal. This new architecture poses the new defi and offer the new opportunities for the project development management from ITproject chief. If our readers desire acquire one client/server system basis knowledge generally, we send it to one of the multiple test existed on the subject.
7.1.One introduction to the client/server environment.
The client/server concept can apply to 2 modal of basis: the modal development environment and the modal application environment. In one development environment, one cl;ient/server system is a tool of development faciliating the IT project development. In the application environment, one client/server system supplies one specific service. In the point of vue more general, one can consider that 2 modal appeared, one development tool focus them also a specific service. The following examples indicate the difference between 2 modals.
The client/server network is a good environment example of client/server development. In this example, each developer has one client computer. The developers communicate due to the server network and client computer and partage these resources(for example, espace disc or the printers) reliant to servers.
One automatic distributor network is an example of client/server application environment, where each client is a distributor and each server is a regional computer(or central). Here, the client/server concept is pplied to one architecture existed before client/server term apparition. Although this example includes the basis elements of basis of one client/server application system, it has not someone of gadgets following the modern client/server system(like the direct communication between clients).
One other example of client/server application environment is that o9f stock system where computer clientare used for the setting up all transactions and demands and computers server(it can have a lot)to make access to the given bank and printing.
7.1.1.Definitions and terminology
One client/server environment is one multitreatment environment together with command computer(clients) and divided treatment computer where each user has one personnalised rapport to the system.
The key words of this definition are:
-“associated”, making accent of one good definition of communication protocole
-“divided” is defined the specific character of client/server environment.
-“personnalised” implicates that each user(client) don’t have knowledge of resources used by other users.
By the ideal manner, users have one image of the unique system(ISU) make them believe that they have the total system for them. This rapport personnalised to system, in the most of cases, still one ideal dream. In reality, only targets of associated environment and divided resources are completely attaint.
It exists numerous variations of client/server environment. The postes of work Sun are frequently used as client/server development environment, and PC network(like Novell) are always used as application environment. These environments woule become client. In reality, in certain client/server environment, all client can also be configured as server.
The servers can communicate between them, such as interior of unique client/server system, or between different client/server systems. In the larger context, the client/server system can be connected between them by the biais of long distance networks(RLD) and form logically client/server systems extremely important. Conbsidering, for example, the case of multinational society having the development centers in a lot of countries. Whe each country can have their own client/server own system, the society in all the ensembly can be connected to one international long distance network. Then, one client in France, can divide resources situated in United States. In the frame of important ameliorisation of world communications and with expansion of big international societies, this kind of development environment become preponderant.
In the IT development environment, we will compare one client/server system to centralized IT system(minicomputer of gross computer) and to decentrialised IT system(micro computer). In the last case, a lot of advantages appear: the possibility of divide of fiches of given and of information transfer in real time between users.
The centralialised system don’t supply strongly one environment of development worser than one client/server environment. Centralialised environment has the advantages, like the weak cost of one supplementary user(the cost of one non-intelligent terminal) and the relatively strong power of central computer. Therefore, this is in term of polyvalue and weak cost of entry that client/server system are advantageous. By the ideal manner, the client/server environment development is to focus the posts to work for the development at the weak cost and at the high integration degree. In entry, client/server environment is very cheaper. The investment of depart is weak and the complementary of new posts of works is relatively cheaper(although superior at the cost of one non-intelligent terminal). Virtually, the environment can make big infiniment.
The integration degree between posts of development works is function of kind of client/server system, by the manner that it is configured, the used progiciel and norms of applied development. Certain specific progiciel (like the configuration management) ask one high degree of enterprise determining finally of development activities have to be cordoned strictly.
Same in outside of development environment, client/ser application system have the similar targets. They offer one high integration level and one weak entry cost for the small systems. Taking example of automatic ticket distribution system. The smalls like the big banks can same take on place similar distribution systems and better, can communicated between them for possible crossed transactions.
It is clealy that the distributor network is integrated highly and the complement of one new distributor is relatively simple and cheaper.
7.1.3.Functions of client.
The client computer assure the interface between the system and the user. The composants of modern computers client use classically one graphic user interface(IUG) like that of windows, windows NT, X-windows or motif. This kind of interface allows user one form of communication intuitive with the system, at the same time easy to the user and to manage.
The client is the mediator between the user and the server; it needs of server services. At the most elementary level, the architecture is similar to this:
user↔client computer↔server computer.
One of the principal differences between the simple terminal and one client is that the client has the authority to execute their own logiciel applications. The client stay habitually the module of logiciel general system presentation; this is why it is responsible of reforming and attaching informations in the exit of system. The client realize also the initial conversion and also if that is possible to treat initially of entries of user.
Different computer clients one the same client/server system can have different logiciel of presentation and IUG different user. It is not rare that rely one post of work Xerox, one post PC MS-Windows and one Macintosh at the same client/server network. In reality, all the terminal computer can function like one client computer for more client/server interface norm respectation(designated commonly by interface API).
7.1.4.Functions of server.
One of the principal functions of server is to supply services to their clients. These services will access to peripherics and networks, at the teletreatment on the same server. Ideally, the server hide client the complexity of client/server network.
Other major functions of server, it is the access control to the given. The servers manage important bases of the given, to which clients or same of other servers, in certain cases, have access, by the biais of important complex networks. The server has the control of given manage the access control(for example, the protection incompatible or concurrents, at the first place outside of the setting up of the given.
In the frame of the local RL networks and long distance networks RLD, the server functions like the passerelle give to the computer client one access to the whole world. This important characteristic authorize also access from the exterior world to the client/server system virtually from some place. The access is made possible,such as the accorded networks in permanence to others or by connecting(by one modem) to other networks. And then all computer with one modem can virtually function like one far client.
Multiple server is not strongly synonymous multiple client/server system. One unique system can have more than one server. In the frame of one system at multiple server, the server function like one associated system gone the tasks between servers, by the kind that one of servers could manage the basis of the given, one other transmissions and one third treatment of applications. The complexity of this kind of system is dissimulated to clients by each server, clients then don’t conscience to the existence of a lot of servers.
Noting that clients can also be servers. All peripheric unity connected to one client, or all other resource client, can be sent disponible to other clients by positioning client computer on the double mode client and server. Although all the architectures client/server don’t represent this characters of double mode, numerous are that the font(like network PC of IBM)
The network is the principal axis of all client/server system allowing one easy access and connections between button. This concept of network in couches (see the table 7.1) that people design by the term of architecture in interconnection of open system OSI(open system interconnection). OSI architecture is conceived for leeting interconnextion of different kinds of systems. Not making apanage of client/server system, possible to rely the networks at the stages of one societies, of one state and same globe. OSI architecture is common, by not being indispensable, in the client/server system.
Table 7.1. The modal in couches OSI.
Số couche- couche numero
Lọai thong tin –information kinds
Mô tả -Description
Supplying one API interface to the client/server application
Translation of the given in format of representation for user
Allowing communication between applications of different processors.
Allowing information of one point to another by the network
Transfer of information sequences by physical lines.
Transmission of bit trains by physical liaison
7.2.1. Network protocole
The liaisons of network that the connect clients and servers or networks between them, necessitate the protocols: the regulations on the coopratioon between the networks and composants of networks. One of the most classical protocole of communication is the protocol designated by the sigle TCP/IP( transmission control protocol/internet protocol). TCP/IP is in reality one serie of protocols for locals networks and big distance, it is developed at the origin for the systems under Unix. For the client/server architectures,there are the IP(internetwork protocol) client/server protocol functioning with TCP/IP.
It exists numerous other protocol of communication at the different level, such as SNA(systems network architecture) used by IBM, the Netware of Novell and Lan manager protocol of Microsoft. While OSI architecture, defined by ISO(international normalization organization), is interesting particularly in the client/server environment because it represents the heterogene system connection possibility. There are 7 couches OSI, determining different levels of management, of access and network application. These couches are described in the table 7.1.
OSI don’t signify unique “interconnection”; that signifies also “open”. The open networks offer one easy access at all network element respecting one ensembly of fundamental regulations or norms. These ones manage the stockage and access to the given, same as the functioning of network elements. “open” signifies fundamentally that all network element forms to regulations of functioning and access can have access to all other elements of the networks(there are not the restrictions for the security reason). This is why OSI is considered like being the ideal architecture of one client/server network.
7.2.2.Reflexions on the networks
One easily made interconnection is one significant advantage for the geographically gone project management, it means when development equip members are situated on far sites. Associated to the development tools appropriated gone(for example, the managers of configuration, registering of errors, access control, electronic correspondence), one interconnection can supply necessary environment for creating from the distinct groups.
For the project chief, the open networks allow also not imposing platform of identical development. One open network can have the far developers using posts of work Sun, PC or Informix. It is not any case here to advice to project chiefs to encourasge the utilization by their developers of different platforms, but to signal that it is possible.
In the application environments, the network supplies also one excellent infrastructure for the gone destinary systems,such as:
– IT network: professional bibliographic reseaches
– Financial system: bank, credit octroi
– Access control: identification system, immigration control
There are fundamentally articulated systems around the given basis and don’t have the unique central given bank. This is the network relying the different stockage centers of given and integrate in one unique access system. The client/server architectures are well appropriated in order to manage the application type in network.
7.3. The advantages and inconveniences of one client/server environment.
For the project chief, client/server architecture, at other architecture of IT system, including at the same time the advantages and inconveniences. The system qualities(or their absence) can have one impact on the manner which project is developed. They influence, at the same time the cible environment, and development environment.
The client/server architecture advantages include:
-the dividing of resources
The resources are used more efficace due to the possibility of divide their using between users.
– The less costs: the initial cost of one client/server system is less than other kinds of mini user systems for the most. Furthermore, the cost of one augmentation of the capacity of system can be inferior also.
– Beginning small and grow: it is not necessary that the project chief fixed from the beginning of the system form; it can begin small and grow in functioning of demands.
– The reduction of systems(decentralisation of treatment)
– Not of falling down due to the unique fault: the risk of falling down of the ensembly of system in the reason of one unique fault is less important than other kinds of systems, also fault of one client computer of not having habitual incidence based on the others.
– Access ton gone given: client/server architecture is one excellent means to supply one access to the gone given for one important number of users in allowing access to the basis of server given due to the important networks.
– -facility of supplementing one new client: the client/server system can bigger easily and not limited theorically, in connecting the client computer supplementary to the network.
– Completing to the relatively simple server: There is not the limite to the server number which counld be connected to the client’server system supplying one power of supplementary treatment, peripherics, one power of accessing to given and functions of system management.
Unhappily, client/server architecture present also some inconveniences:
– System administration: the system administration regulation could be difficult to set up in the reason of high liberty degree existing always at the level of client station./ For example, the given can be stocked locally on the client computer not connected into the global system saver.
– The server surcharge:
– The complementing to server easily signifies not strongly that the servers are supplemented or retired frequently. Then, the servers stay surcharged, that provoke long files of attendant while the capacity of CPU is surpassed, or the local network or transmissions are surcharged, or espace disc is surpassed. In generally, the response time at the time that the demand is stronger, can become mediocre. Although these problems could appear in all kind of systems, they have intention of growing client/server environment.
– The number limited of users having access to modules: When the clients divide the using one of the application module(for example), one graphic module or one tool GLAO), they can be limited by the computer number having the authorization of using simultaneously the module. That signifies that one essay for charging one application sometimes negative.
– One difficult maintenance: Client/server important can understand different computers, peripherics and other material composants: servers,clients, imprimants, discs, routers etc… The plethora maintenance of IT material is one always extremely laborious task.
– One difficult management: The client/server development environment management can be difficult, almost when the servers confers to developers in important independence degree. That is paplrticularly right for the geographically gone development environments.
– Security: The access control security can be difficult to be controlled. It can have a lot of given bases to be protected in different places. The important number of user having access to system can send also extremely difficult the surveillance and the control. That is why it must more than one or 2 measures of security in order to protect one client/server complete network