$1.$ There are many database models. What characterizes the relational database model compared to the other? Name two and briefly explain$/2.$ Besides the relational database model, what other database models are available? Name two and briefly describe them$\mathrm{.}3$How different are conceptual, logical$,$ and physical database models? Give a few examples and explain.What are two examples of structural constraints we use in designing relational database models? Briefly explain each. Provide answers for this as short answers