During requirements analysis, we identify key objects (things of interest) around which the system is designed. In database parlance, these are called entities. They are objects that are capable of independent existence and that can be uniquely identified. While in object-oriented design the focus is on modeling behavior, entity-relationship modeling is concerned more with attributes and the relationships of entities. In entity-relationship analysis, the relationships are derived from static attributes rather than behavior/interactions, as in the case of object-oriented analysis.
Entities can be usually identified from the nouns in the requirements. For example, in the travel website, a Hotel is a key entity. Requirement analysis gives us insights into the attributes of the entities. For example, the Hotel entity might have the following attributes...
