Data Models

Data Models 

AU: Dec.-14, May-19, Marks 13

Definition: It is a collection of conceptual tools for describing data, relationships among data, semantics (meaning) of data and constraints.

• Data model is a structure below the database.           

• Data model provides a way to describe the design of database at physical, logical and view level.

• There are various data models used in database systems and these are as follows -

(1) Relational model:

• Relation model consists of collection of tables which stores data and also guilatxo represents the relationship among the data.

• Table is also known as relation.

• The table contains one or more columns and each column has unique name.

• Each table contains record of particular type, and each record type defines a fixed number of fields or attributes.

• For example - Following figure shows the relational model by showing the relationship between Student and Result database. For example - Student Ram lives in city Chennai and his marks are 78. Thus the relationship between these two databases is maintained by the SeatNo. Column

Advantages:

(i) Structural Independence: Structural independence is an ability that allows us to make changes in one database structure without affecting other. The relational levsiz model have structural independence. Hence making required changes in thedatabase is convenient in relational database model.

(ii)Conceptual Simplicity: The relational model allows the designer to simply focus on logical design and not on physical design. Hence relational models are conceptually simple to understand.

(iii) Query Capability: Using simple query language (such as SQL) user can get egile information from the database or designer can manipulate the database structure.

(iv) Easy design,maintenance and usage: The relational models can be designed logically hence they are easy to maintain and use.

Disadvantages:

(i) Relational model requires powerful hardware and large data storage devices.

(ii) May lead to slower processing time.

(iii) Poorly designed systems lead to poor implementation of database systems.

1) Entity relationship model:

• As the name suggests the entity relationship model uses collection of basic objects called entities and relationships.

• The entity is a thing or object in the real world.

• The entity relationship model is widely used in database design.

• For example - Following is a representation of Entity Relationship modelin which the relationship works_for is between entities Employee and  Department.

Advantages:

i) Simple: It is simple to draw ER diagram when we know entities and relationships.

ii) Easy to understand: The design of ER diagram is very logical and hence they are easy to design and understand.

iii) Effective: It is effective communication tool.

iv) Integrated: The ER model can be easily integrated with Relational model.

v) Easy conversion: ER model can be converted easily into other type of models.

 Disadvantages:

i) Loss of information: While drawing ER model some information can be hidden or lost.

ii) Limited relationships: The ER model can represent limited relationships as compared to other models.

iii) No Representation for data manipulation: It is not possible to represent data manipulation in ER model.

iv) No industry standard: There is no industry standard for notations of ER diagram.

(3) Object Based Data Model:

• The object oriented languages like C++, Java, C# are becoming the

dominant in software development.

• This led to object based data model.

• To The object based data model combines object oriented features with relationaldata model.

Advantages:

i) Enriched modelling: The object based data model has capability of modelling the real world objects.

ii) Reusability: There are certain features of object oriented design such as inheritance, polymorphism which help in reusability.

iii) Support for schema evolution: There is a tight coupling between data and b applications, hence there is strong support for schema evolution.

iv)Improved performance: Using object based data model there can be significant improvement in performance using object based data model.

Disadvantages:

i) Lack of universal data model: There is no universally agreed data model for an object based data model, and most models lack a theoretical foundation.

ii) Lack of experience: In comparison with relational database management the use of object based data model is limited. This model is more dependent on the skilled egi programmer.

iii) Complex: More functionalities present in object based data model make the design complex.

(4) Semi-structured data model:         

• The semi-structured data model permits the specification of data where individual data items of same type may have different sets of attributes.

• The Extensible Markup Language (XML) is widely used to represent semi- structured data model.

Advantages

i) Data is not constrained by fixed schema.

ii) It is flexible.

iii) It is portable.

Disadvantages

i) Queries are less efficient than other types of data model.

Review Questions

1. Write short note on: Data model and its types. AU: Dec.-14, Marks 8