It is abstract data model, used to represent the data from different data source in single format using Entity Data model (EDM). Entity Data Model represents the logical structure of the data and it does not care how physically data are stored.
It is part of developers to decide how data from different data source is mapped to Entity Data Model. In EDM, each row in a table is mapped to Entity and relationship between tables is represented using association. Association can be unidirectional or bidirectional.
Entity represents the simple structure using Property (column information of row in table) which holds the common data type like Int32, Boolean, String etc
Each Entity has a special type of property called "Navigation Property" which is used to represent the association.
Entity Set stores the collection of Entity and collection of Entity Set are belong to Entity Container. Structure of the EDM is mention below.