A data modelsays what informationis to be contained in a database, how the information will be used, and how the items in the database will be related to each other.
For example, a data model might specify that a customer is represented by a customer name and credit cardnumber and a product as a product code and price, and that there is a one-to-many relation between a customer and a product.
Itcan be difficult to change a database layout once code has been written and data inserted. A well thought-out data model reduces the need for such changes. Data modelling enhances application maintainability and future systems may re-useparts of existing models, which should lower development costs.