Entity Data Model

Entity Data Model

The Entity Data Model aims in providing a single representation for multiple data sources, used by applications.

Large applications often have to deal with data from multiple data sources like XML files, Flat Files, multiple types of databases etc, hence the application will have to use different approaches to communicate with each of the data sources, this makes the data access complex, the Entity Data Model aims in resolving this issue by providing single a Conceptual representation of the data which the application can use, the mapping between the conceptual layer and the data sources are handled using Entity frameworks.

Microsoft provides the ADO.NET Entity Framework which implements the concept of Entity data Model, in the ADO.Net Entity Framework the Entity Data Model is represented using the Conceptual schema definition language (CSDL).

The framework takes care of the mapping between the Entity Data Model and the Data Sources using Mapping specification language (MSL), thus the users have to deal with only one Conceptual data source and not with multiple data sources.

The Entity Data Model also has the advantage of easy portability, suppose we want to change our data source from one provider to another, then we need not modify the application code to achieve this change, it is sufficient enough to change only the mapping between the Entity Data Model and the data source, the Entity Data Model will remain constant irrespective of whatever data source is used by the application.

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ADO.NET Entity Framework

ADO.NET Entity Framework Architecture

Conceptual Data Model

Logical Data Model

Physical Data Model

Conceptual Vs Logical Vs Physical Data Model

Conceptual Vs Logical Vs Physical Data Model

We had earlier seen the different types of data models

Conceptual Data Model

Logical Data Model

Physical Data Model

We shall now see the comparison between these models.

Conceptual Data Model	Logical Data Model	Physical Data Model
Very high level data model	High level data model	Low level data model
Only Entities (Tables) are defined	Entities & Attributes (Tables & Columns) are defined	Entities,  Attributes & Properties (Tables, Columns, Data Types & Size are defined)
Developed during the initial requirements phase of the project.	Developed during the late requirement / early design phases of the project.	Developed during the final design phase of the project.
Remains constant across databases	Remains constant across databases	Varies based on the target database.
Used to give a high level picture to the Business users.	Used by the Database administrators to Normalize and optimize the database.	Used more by the developers to develop the application.

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Conceptual Data Model

Logical Data Model

Physical Data Model

Conceptual Data Model

Conceptual Data Model

The conceptual data model is a very high level data model which just shows the various entities (Tables) in the model and the relation between the entities.

This data model can be used during the initial high level design phase where the requirement clarity is restricted only to the key entities, the details of their attributes are not known at this point in time.