The need for methods
The design of an information system is not obvious because itmust consider the entire organization that we must implement.The design phase requires methods toup a model on which it will rely.The modeling is to create a virtual representation of a reality so to emphasize the points that are of interest.
This type of method is called analysis. There are manymethods of analysis, the most common method being the method in France MERISE.
Introducing the method MERISE
MERISE is a method of design, development and implementation of IT projects.The goal of this method is to get to design an information system. MERISE method is based on the separationand data processing to be performed in a number of conceptual and physical models.
The separation of data and processing ensures longevitymodel. Indeed, the arrangement of data need not be oftenredesigned, while the treatments are more frequently.
The method MERISE date of 1978-1979, and follows a national consultationlaunched in 1977 by the Ministry of Industry in order to select companiesIT consulting to define a system design methodof information. The two main companies that have developed this methodare the CTI (Computer Technology Center) to manage the project,CETE (Center for Technical Studies of Equipment) based in Aix-en-Provence.
abstract design cycle of information systems
The design of the information system is done in stages in order to achievea functional information system reflecting realityphysical. It is therefore to validate one by one each step takinginto account the results of the previous phase. On the other hand,data being separated treatments, checkthe correlation between data and processing to ensure that alldata required for processing are present and there is no unnecessary data.
This sequence of steps is called abstraction cycle for system designof information :
The expression of needs is a step to definethat is expected of the automated information system, this requires:
- to inventory the elements necessary information system
- delimit the system by learning from the future users
This will create the MCC (Conceptual model of communication) whichdefines the information to take into account flows.
The next step is to develop the MCD (Modelconceptual data) and MCT (Conceptual Model of treatment)describing the rules and constraints to consider.
The organizational model is to define the WORD (Modelorganizational treatment) describing the constraints due to the environment (organizational, spatial and temporal).
The logic model is a software option for the information system.
The physical model reflects a material choice for the information system.
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