Data Model means, to give a SHAPE to the data. A Data Model Makes it easier to understand the Data. We can define the data model as "The Collection of High-Level data description that hide many low level storage details".
The Data Models are divided into THREE different groups. They are,
- Object - Based Logical Models
- Record - Based Logical Models
- Physical Data Models
1. Object Based Logical Models : These are used in describing data at Logical Level and View Level. ( Logical level describes what data are stored in the database and what relationships exists among those Data. This logical level is used by the DBA (Data Base Administrator). He must decide what information is to be kept in the Data Base. The View level describes Only part of the entire database to be viewed by the user of the database hiding the details of the Information Stored.
The Object based logical models are described in the different following models.
- The E-R (Entity-Relationship ) Model
- The Object-Based Logical Model
- The Semantic Data Model
- The Functional Data Model
E-R Model : The entity is a "Thing" or " Object" in the real world that is distinguishable from other objects. The E-R model is based on the collection of basic objects called Entities and the Relationship among them. Consider the following Diagram.
In the above diagram, RECTANGLES represents ENTITIES, DIAMONDS represents RELATIONSHIP among those ENTITIES. LINES represents links of Entities to Relationships.
Object - Oriented Model : The Object Oriented model based on a collection of OBJECTS. An object contains values stored in Instance Variables and Bodies of Code that operates on the Object. (These bodies of Code is called Methods).
Objects that contain the same types of values and the same methods are grouped together into classes. (A class is the definition of the object).
Semantic Data Model : A Semantic data model is a more high level data model that makes it easier for a user to give Starting Description of the data in an organization. (Semantic is nothing but the Meaning). These models contain a wide verity of relations that helps to describe a real application scenario. A DBMS cannot support all these relations directly. So it is build only with few relations known as relational model in DBMS. A widely used semantic data model is the Entity-Relationship (ER) data model which allows us to graphically denote entities and relationship between them.
Functional Data Model : The functional data model makes it easier to define functions and call them where ever necessary to process data.
2. Record - Based Logical Models :
In this type of models, the data is kept in the form of RECORDS (documents). Thse models describes data at Logical and View Levels. When compared with Object Based Data Models, the record based logical models specifies the overall logical structure of the database and provides higher-level implementation.
These are of 3 types. Those are,
- Relational Model
- Network Model
- Hierarchical Model
Relational Model : The relational model represents both Data (entities) and Relationships among that data in the form of Tables. Each table contains multiple columns and each column contains a unique name. Have a look at the following table.
Network Model : Data in the network model are represented by collection of Records and Relationships among data are connected by LINKS. These links can be viewed as Pointers. Have a look at the following diagram.
Hierarchical Model : This is also same as Hierarchical model, the difference is the records in the database are represented in the form of TREES (in Hierarchical way)
3. Physical Data Models: Physical data models are used to describe data at the lowest level, which explains how the data is actually stored using complex low-level data structures. Actually, the physical data models are rarely used.
There are two types in Physical Data Models.
Hierarchical Model : This is also same as Hierarchical model, the difference is the records in the database are represented in the form of TREES (in Hierarchical way)
3. Physical Data Models: Physical data models are used to describe data at the lowest level, which explains how the data is actually stored using complex low-level data structures. Actually, the physical data models are rarely used.
There are two types in Physical Data Models.
- Unifying Model
- Frame-Memory Model
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