Data Entity represents a data subject from the common data model that is used in the logical data model.
A Data Model has three theoretical components. The first is the structural component which is a collection of data structures which will used to represent entities or objects in the database. The second is the integrity component referring to collection of governing rules and constraints on data structures. The third is the manipulation component referring to a collection of operators that can be applied to data.
Data Entity is one the components defined in a logical data model. A logical data model is a representation of all of the organizations data which are being organized in terms of data management technology. In today’s database technology, there exist choices for logical data models relating to relational, object oriented or XML. Relational refers to the Data Entity as described in terms of tables and columns in the database. Object oriented Data Entity refers to the terms used in classes, attributes and association. XML Data Entity refers to terms described in tags similar to the web’s HTML.
But whether it is relational, object oriented or XML, a Data Entity is the computational equivalent of a real life person, object, events or activities. A Data Entity should strictly adhere to the structures identified and defined in the conceptual data model because it describes the semantics of a business.
An entity defined in the conceptual data model may be any kind of thing about which a company wants to contain formation, attributes pertaining to the information and relationships among the entities. For example, a company may have a person entity stored as "CUSTOMER" Data Entity in its database. Or it could be the other way around as having an abstract entity "PERSON" which may represent different real life entities such as customers, vendors, managers, suppliers and many more which are being defined in the conceptual data model. Conceptual data model is about definition of abstract entities and these definitions are being done in a natural a language.
The Data Entity is actually defined in the logical data model which is actually the underlying layer to a physical implementation of a database. Based on the abstract entities from natural language defined entities of the conceptual data models, the placement of data entities in columns is specified. The logical data model allows an end user to access and manipulate a relational database without him or her having to know the structure of the relational database itself. As such, the first part in creating a logical data model is in fact specifying which tables are available and then defining the relationships between the columns of those tables. It is in the logical data model where the definition of the structure for the data field of the Data Entity having a master level and a plurality of detail levels can be found.
As good illustration of a Data Entity is a relational model. From the abstract entity defined in the conceptual data model, a logical Data Entity is laid out in columns of a relational table.
The table is the basic structure of a relational model and this is where information about the Data Entity, for instance, an employee, is represented in the columns and rows. The values of a named columned are called attributes of the Data Entity. The term relation refers to the many tables within the database. For example, a column in the employee table enumerates all the attribute pertaining to the employee such as name, gender, age, address, marital status and others. The row is actually an instance of an entity represented in the relation.