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What Are Data Models In DBMS ?

Data models are a collection of conceptual tools for describing data, data relationships, data semantics and data consistency constraints. A data model provides a way to describe the design of a database at the physical, logical, and view levels. There are main three different data model Types and they may further divided into subcategories which are as follows :

1. Object-based Logical Models

1.a.   The E-R Model  (Entity-Relationship)
1.b.  The Object-Oriented Model  

2.Record-based Logical Models

2.a. The Relational Model.
2.b. The Network Model.
2.c. The Hierarchical Mode.

3. Physical Data Model.

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1.  Object-based logical models:

    • Describe data at the conceptual and view levels.
    • Provide fairly flexible structuring capabilities.
    • Allow one to specify data constraints explicitly.
    • Over 30 such models, including
      • Entity-relationship model.
      • Object-oriented model.
      • Binary model.
      • Semantic data model.
      • Infological model.
      • Functional data model. 

­1.a. The E-R Model

  1. The entity-relationship model is based on a perception of the world as consisting of a collection of basic objects (entities) and relationships among these objects as it's name itself suggests .
    • An entity is a distinguishable object that exists.
    • Each entity has associated with it a set of attributes describing it.
    • E.g. number and balance for an account entity.
    • A relationship is an association among several entities.
    • e.g. A cust_acct relationship associates a customer with each account he or she has.
    • The set of all entities or relationships of the same type is called the entity set or relationship set.
    • Another essential element of the E-R diagram is the mapping cardinalities, which express the number of entities to which another entity can be associated via a relationship set.
We'll see later how well this model works to describe real world situations.
  1. The overall logical structure of a database can be expressed graphically by an E-R diagram:
    • rectangles: represent entity sets.
    • ellipses: represent attributes.
    • diamonds: represent relationships among entity sets.
    • lines: link attributes to entity sets and entity sets to relationships. 

The E-R Model Example

1.b Object-based logical models:

Object-oriented programming (especially in Java, C++, or C#) has become the popular software development methodology. This led to the development of an object-oriented data model that can be seen as extending the E-R model with notions of encapsulation, methods (functions), and object identity. The object relational data model combines features of the object-oriented data model and relational data model.
  • Describe data at the conceptual and view levels.
  • Provide fairly flexible structuring capabilities.
  • Allow one to specify data constraints explicitly.
  • Over 30 such models, including
    • Entity-relationship model.
    • Object-oriented model.
    • Binary model.
    • Semantic data model.
    • Infological model.
    • Functional data model.

2. Record-based logical models:

    • Also describe data at the conceptual and view levels.
    • Unlike object-oriented models, are used to
      • Specify overall logical structure of the database, and
      • Provide a higher-level description of the implementation.
    • Named so because the database is structured in fixed-format records of several types.
    • Each record type defines a fixed number of fields, or attributes.
    • Each field is usually of a fixed length (this simplifies the implementation).
    • Record-based models do not include a mechanism for direct representation of code in the database.
    • Separate languages associated with the model are used to express database queries and updates.
    • The three most widely-accepted models are the relational, network, and hierarchical.
    • This course will concentrate on the relational model.
    • The network and hierarchical models are covered in appendices in the text.

2.a The Relational Model.

  • Data and relationships are represented by a collection of tables.
  • Each table has a number of columns with unique names, e.g. customer, account.
The Relational Model Example.

2.b The Network Model.

  • Data are represented by collections of records.
  • Relationships among data are represented by links.
  • Organization is that of an arbitrary graph

The Network Model Example.

2.c The Hierarchical Model.

  • Similar to the network model.
  • Organization of the records is as a collection of trees, rather than arbitrary graphs.
The relational model does not use pointers or links, but relates records by the values they contain. This allows a formal mathematical foundation to be defined. 

The Hierarchical Model Example.

3. Physical Data Models

  1. Are used to describe data at the lowest level.
  2. Very few models, e.g.
    • Unifying model.
    • Frame memory.
What Are Data Models In DBMS ? Reviewed by Hardik Pandya on 12:04:00 AM Rating: 5

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