Data Models

The structure of the database is called the data models.A Collection of conceptual tools for describing data, data relationship, data semantic and consistency constraint.

There are three different groups.
  • Record-based logical models
    1. Relational model
    2. Network model
    3. Hierarchical model
  • Object-based logical models
    1. The entity-relationship model
    2. The object-oriented model
    3. The semantic data model
    4. The functional data model
  • Physical models
    1. Unifying model
    2. Frame-memory model

Record-based logical models

  • Record based logical models are used in describing data at the logical and view levels.
  • Record-base models are named as database structure have fixed format records of several types.
  • Each record type define a fixed number of fields or attributes.
  • Each attributes and each fields is a usually of a fixed length.

  • There are three most widely used record-based models are:    
    • Relational model:
      • The relational model uses a collection of tables to represent both data and the relationships among those data.
      • Each table has multiple columns, and each column has unique name.
    • Network model:
      • Data in the network model are represented by collections of record and relationships among data are represented by links, which can be viewed as pointers.
      • The records in the database are organized as collection of arbitrary graphs
      • Advantages Network model :
        1. Conceptual Simplicity
        2. Ease of data access
        3. Data Integrity and capability to handle more relationship types
        4. Data independence
        5. Database standards
    • Hierarchical model:
      • In hierarchical model the data and relationships among the data are represented by records and links.
      • It is same as network model but differs in terms of organization of records as collections of trees rather than graphs.
      • Advantages Hierarchical model :
        1. Simplicity
        2. Data Security and Data Integrity
        3. Efficiency
      • Disadvantages Hierarchical model :
        1. Implementation Complexity
        2. Lack of structural independence

Object-based logical models

  • Object-based logical models are used in describing data at the logical and the view levels.
  • They provide fairly flexible structuring capabilities and allow data constraints to be specified explicitly.
  • There are many different models more widely know ones are:
    1. Entity-relationship model
    2. Object-oriented model
    3. Semantic model
    4. Functional data model

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