4. Data models : DTDs and schemas

4.1 Notion of generic model (or schema)

Taking the example of figure 1 , we can imagine that the creation of a weather report is subject to a certain number of constraints concerning its structure (the type of data it contains and their relative organization) and possibly its content (the values of these data). For example, it can be assumed (as a structural constraint) that information on date, time and geographical location is essential, but that the list of measured parameters may vary within certain limits, depending on the weather station's equipment. We can also assume (content constraint) that the data measuring relative humidity...