DATA MODELS

A model is a representation of reality or real world, where objects/events and their association exists.

Data model is the organisation of database in DBMS. It is the way in which data is structured and planned.

Data model provides the basic concepts and notatations that are used to describe the structure of the database including types, relationships and constraints which should apply on the data.

Data Models fall into three basic categories:-

  • Object Based Data Models

  • Physical Data Models.

  • Record Based Data Models.

  • Sorting the information in ascending/ descending order.

Object Based Data Models:

Object Based Data Models are also called Conceptual Models.

These are used for defining concept such as entities, attributes and relationships.

These models are used in describing data at the logical and user view level, commonly used object based data models are:

  • Entity-Relationship Model

  • Object Oriented Model

  • Semantic Model

  • Functional Model

Physical Data Models:

Physical Data Models are used to describe the concepts that describe the details of data storage, i.e. how data is stored in the computer along with record structures, access paths and ordering.

The most commonly used physical data model being the unifying model.

Record Based Data Models:

Record Based Data Models are used to describe the data at the conceptual view level, here, database is structured in fixed format records of several types.

Each record type defines a number of fields and each field is usually of a fixed length. The various types of record based data models are:-

  • Hierarchical Model
  • Network Model
  • Relational Model

Hierarchical Model:

A hierarchical database model is a data model in which the data is organized into a tree-like structure.

The data is stored as records which are connected to one another through links.

It employs two basic concept: Record and Parent Child Relationship

A record is a collection of field values which provided information of an entity and parent child relationship is 1: N relationship between two record types.

This model requires that each child record can be linked to only one parent and child can be reached through its parents only.

Advantages of Hierarchichal Model:

  • Since the records are in the form of parent-child relationship, performing various operations is simple.

  • Each child is linked to only one parent, nd child can be reached through its parent only, so data integrity is promoted.

  • It is very efficient to handle large number of transactions using this model.

  • A child can be reached through the parent, and for deleting a child record, parent segment is needed, thus security is maintained.

Disadvantages of Hierarchichal Model:

  • This model is not flexible to represent all the relationships which exist in real world.

  • Many to many relationship cannot be represented.

  • It cannot demonstrate the over all data model for the whole of the enterprise because actual data is not available at the time of designing of model.

  • A good knowledge of physical data storage is required for its implementation.

  • Additions, deletions and updations are not easy.

  • Querying facilities are not efficient and adequate.

Network Data Model:

Network data model is similar to hierarchical model, but it has slight improvements.

Here we can have multiple parent-child relationships, i.e . many to many relationships can be represented.

It allows a record to have more than one parent.

Here, directed graphs are use instead of tree structures in which node can have more than one parent.

Therefore, it is best suited for handling non-hierarchical relationships.

Advantages of Network Model:

  • In this model, a record occurs only once without repetition, so lesser storage requiremnts are needed

  • A large number of different relationships like one to one, one to many, many to many etc. exists, so many types of relationships can be handled.

  • The data access is easier and flexible.

  • It is conceptually simple, so it is easy to design.

  • A member record cannot exist without an owner record, so integrity is maintained.

Disadvantages of Network Model:

  • Querying is difficult because the programmer has to think about links and how to traverse the links.

  • All the records are maintained through pointers, hence database structure becomes complex.

  • Additions, deletions and updations require a large number of adjustments.

Relational Model:

It is considered to be the most significant development in database technology because it is used for representing most of the real world objects. and the relationships amongest by Dr. E.F. Codd, a researcher of IBM in 1970.

The relational model consists of three major components:

  • The set of relations also called tables and set of domains, which define the way data can be represented.

  • The set of rules for maintaining the integrity of the database.

  • the set of high level operations that can be performed on data.

It is defined as a database which allows you to group its data items into one or more independent tables that can be related to one naother by using fields common to each related table.

each table consists of rows, also called tuples and columns, also called attributes.

This model does not require any information that specifies how the data should be stored physically.

Therefore, it is best suited for handling non-hierarchical relationships.

Basic terminology used in Relational Model:-

List of relational terms and their meanings are given below:

Relation——Table 
Attribute——Field
Tuple———-Row/Record
Domain——-Set of Legal values
Degree——–Number of columns
Cardinality—Number of rows
Primary Key—Unique Identifier

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Advantages of Relational Model:

  • It provides flexibility which allows frequent change to databse structure.

  • It is simple to design and implement. The user has to concentrate on the logical view of the database rather than how it is stored.

  • In relational database, it is possible to make changes to the database structure without changing application based on structure.

  • It has the presence of powerful, flexible and easy to use query capabilities.

  • It is useful for representing most of the real world objects and the realtionship among them.

Disadvantages of Relational Model:

  • Relational database system needs more powerful hardware and store devices to run smoothly.

  • The ease of design and use can lead to the development of poor design database systems.

  • Relational database are not sutitable for large databases.

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