A schema diagram contains a series of interconnected components. To quickly identify the
relation between two connected components, the connection is represented as:
- a thick line to identify a connection with a required component (in the following image,
family is a required element);
- a thin line to identify a connection with an optional component (in the following image,
email is an optional element).
The following topics explain in detail all available components and their symbols as they
appear in an XML schema diagram.