Let’s look at another simple example of data modelling. EPANET is a public domain software package which models water distribution systems. Written by the Water Supply and Water Resources Division of the US Environment Protection Agency (EPA), it is available as either an interactive network editing program, or a toolkit that allows the analysis engine [...]
We have now looked at the background of data modelling and where it all began. Clay tablets, lists, books and now databases. But behind all of these is the need to model the data in a way that makes it easy to use. In this way, data modelling is both a simple and complex area [...]
We have reviewed data modelling connection types over the past several weeks (see Connections) and seen that a few simple names can describe different types of connections in a general way: One-to-one (mandatory or optional). One-to-many (see One-to-many-relationships). Many-to-one. Many-to-many (see Many-to-many relationships). […]
A many-to-many relationship is also best shown by example. One author can write many books – this is a one-to-many relationship. However, one book can also have many authors. Putting these two facts together, we see a many-to-many relationship. Two “one-to-many” relationships in opposite directions. Since this is not always easy to understand, let’s look [...]