It describes HOW the data is structured on the storage devices and HOW it will be accessed. For information systems that are not event-driven, therefore, the process and data models, in an important sense, complement each other. They represent sets of objects and are represented by rectangles on the entity-relationship diagrams. For example, employees, invoices, purchase orders, customer orders, remittance advices, customers, vendors, products, are all entities in the accounting context. It should be clear that the thing of interest to us are sets of objects.
Individual object belongs to a set.
They represent relationships between entities and are represented by diamonds on the entity-relationship diagrams. These are characteristics that describe entities. Similarly, a vendor has a name, address, Fax number, and so on. These characteristics that describe individual objects in an entity set and are called attributes. The attributes take value for a particular object from a domain of values for such attributes.