General: Information Systems/Example of a production company and General description

The information systems are declined according to the nature of the information which they manage and according to the use which is made of it:

 *that can concern the activities of a company or an administration or the technical data of a laboratory or the elements of documentation of an information center.

 *The organization of data can be realized in many ways and take many forms.

 *The realization of such a system must meet the needs of the users and its implementation requires the adoption of an approach that will allow defining precisely its characteristics so that the expected functionalities exist.

  *An accounting-invoicing application will not the same audience and will not require the same organization, nor the same information as an information as a production follow-up application.

 Even if these two types of applications

sometimes share common data.

 *They can also be declined in a single system managing all the information in a centralized way or

in several practically independent sub-systems that may have gateways. 

 *The degree of sophistication varies from one system to another depending on the needs

 and resources of each one.

In the case of a company, for example, all departments handle information:

1) the purchasing department;

2) the production department ;

3) the sales department;

4) the personnel department;

5) the support departments.

 internal to the department for its own operation, internal to the company but external to the department when it is a question of exchanges with other departments

and strictly external when this flow leaves the company: 

with customers, suppliers, and banks for example.

 The data strictly internal to the department only depend on its own organization, while the other types of data must take into account the constraints of other related to the other parties involved. 

The purchasing department is thus concerned about exchanges between internal departments for requests, and suppliers and banks for responses. In order to function, it is necessary to have access to all the information concerning these exchanges.

 In this way, This is how it builds up its own information system. It needs a minimum of data to trigger operations such as a request from another department and creates its own information for suppliers in the form of information to suppliers in the form of purchase orders. 

The data that it for its own needs, for example, to trigger an action, is referred to as input data and the data it and the data it creates is called output data. 

It must also provide reports summary reports to the company's managers, reports obtained by synthesizing the elementary information that he has manipulated to carry out his missions. 

These statements can be calculated by the service itself and be transmitted in one form or another to the requesting parties, but they can also be directly available if the latter has access to the data.

 It thus participates in the information system of the company by enriching the description of its functioning.

The constitution of an information system requires a thorough reflection in order to meet the expectations of future possible to the expectations of future users.

 For this reason, we must distinguish three approaches to information systems corresponding to three levels of concern.

 The first level is called the conceptual approach, the second the logical approach and the third corresponds to the concrete realization of the latter. 

These three levels can correspond to three types of the project owner who wants to set up a system in order to solve operating problems, the problems, the project owner who has to find a solution to meet the project owner's request, and that of the developer who will create the system.

 These levels of concern are translated into action by the main steps of a process aimed at ensuring the success of the system to ensure success the system, steps that are recommended when a study is launched to implement or improve an application using an information system. 

The conceptual level specifies the actors involved and the functions performed by the information system as well as The conceptual level specifies the actors involved and the functions performed by the information system as well as its limits of use, i.e.

 the functions that it does not perform (What do we want to do?). 

 what is the

realized: what is the necessary information and which treatments are going to use it in order to realize the objectives (How are we going to do it?). 

The design at this level of the system only takes into account

the requested functionalities independently of the technical means used for its realization. 

The last question is: With what do we realize the information system? It is intended to intended to specify the tools used and to estimate the developments to be made.

There is a fundamental principle to be applied in all circumstances: the independence of processing and data to ensure the scalability of the system. 

Indeed, this principle, which is simple to state but more difficult to achieve guarantees that if it is applied the form of the data does not interact with the developments and vice versa.

 This means that if the data changes, the existing processes will continue to work and in the same way, any modification of the processes will be possible with the existing data.

The independence between the two components of a system will not be realized if for example the data a particular structure or specific properties such as a particular order in the list of attributes.

The MERISE or UML methods are perfectly adapted to the implementation of an information system and include the three previous levels: conceptual level, logical level, and realization level.

 The MERISE method, for example, imposes a study according to these three levels for both the treatments and for the data.

 By carrying out this double approach we respect by default the principle of independence since the study on the treatments will be carried out independently of that on of the one on the data. 

The conceptual data model (CDM) specifies the necessary elements,

The logical data model (LDM) translates the conceptual model into concrete terms by indicating the properties of each element.

The conceptual processing model (CPM) indicates the functionalities to be provided and the methods to achieve this.

The logical processing model (LPM) describes the different operations necessary to obtain the previous functionalities.

The implementation of the data and the development of the processes constitute the remaining levels.

The step-by-step approach allows, in particular, to take into account the hardware constraints only at the end. 

This guarantees the reuse of the conclusions of the previous stages, which is particularly interesting in order to ensure the This is particularly interesting in order to ensure the maintenance of the system. 

A modification of a conclusion of a step will only have an influence on the following steps.