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.
7.1.2.client/server
targets.
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)
7.2. Network
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
|
Tên-Name
|
Lọai
thong tin –information kinds
|
Mô tả
-Description
|
|
7
6
5
4
3
2
1
|
Application
Presentation
Session
Transport
Network
Phisical
interface
|
Messages
Messages
Messages
Messages
Paquets
Trame
Bit
|
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
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