We already know that the classic approach of an IT project includes the following stages:
- Analysis of the existing situation and needs;
- Creation of a series of models, which allow to represent all the important aspects;
- From the models, implementation of a database.
Regarding the first step, we are not going to introduce real rules, but simply use our knowledge of running a business, our open mind and even our fantasy to properly analyze the existing situation and the needs of users. The result of the analysis is generally one or more documents, which contain the main indications on the desired functioning of the computerized system. The analysis document often already contains prototypes of certain important documents, which the future system should be able to produce.
Once the analysis is complete, the next step is to develop a series of models, based on the analysis document. These models will allow us later to implement a database, which will contain all the information necessary for the proper functioning of the computerized system.
Every analysis method contains the following three-level of analysis
The conceptual level
The conceptual level, which is based directly on the analysis, describes all the data in the information system, without taking into account the IT implementation of this data. This level, which therefore represents the meaning of the data, results in a formalism that we call : Conceptual data model
The logical level
The logical level, which is based on the conceptual data model, takes into account the implementation of the information system by a DBMS. This level introduces the notion of logical tables, and therefore constitutes the first step towards the DBMS tables. This level is represented by: Logical data model
The physical level, which is based on the logical data model, finally contains the tables defined using a specific DBMS (eg MS Access, dBASE, Oracle, etc.). This level is represented by: Physical data model
Here are the 4 steps necessary to translate a natural information system into a database: