Data Models, Schema and Instance

Data Models

Data models refers to how the logical structure of a database is made. Data model acts as a conceptual tool that describes the data relationship, data semantics and data constraints. Database uses three tier architecture so we need to design the database at physical, logical and view level.

Categories of data model are −

Relational Data Model

In this model, the data is designed in form of rows and column within a table. The tables are then going to establish the relationship among the data. Tables are referred as relations because the relationship among the table or data is going to be stored in relation only. It is also referred as a record-based model and is most widely used data model. This model was initially described by Edgar F. Codd, in 1969.

ER(Entity-Relationship) Data Model

It consists of a collection of basic objects called entities provided by relationships among the entities. A entity is a real world object and is distinguishable from other objects. This model was designed by Peter Chen and published in 1976 papers.

Object-based Data Model

It is actually using the ER Model with object-oriented features like encapsulation, inheritance etc. This model is used in systems with structured and collection types.

Semistructured Data Model

It deals with the specification of data. i.e. individual data items of the same type may have different sets of attributes. This data model is mainly used for transferring the data among the applications. The language that supports is XML(Extensible Markup Language).

Schema

It is used to logically represent the structure of a database along with the relationship and organisation between them. It is considered as a blueprint of a database which shows the relationship between tables.

Types of Schema

Conceptual schemas

It is used to gather initial requirements of projects by offering a detailed view of the system.

Logical database schemas

It implies the rules that govern the database and define schema with tables, view, relationship and integrity constraints.

Physical database schemas

Data gets stored within disk storage i.e. this schema refers to actual storage of data.

Instance

The collection of information stored in the database at a particular moment is called instance. It contains a snapshot of database. The data present in the database can be changed frequently. Database instance is equal to the value of the variable.

Conclusion

This article consists of data model, schema and instance. Data model refers to the structure of database. Data model consists of four categories i.e. Relational datamodel, ER model, object-based model and semistructured model. Schema refers to the logical representation of database provided with relationship shown. Types of schema are conceptual, logical and physical schemas. Instance is a snapshot of a database i.e. information stored in a particular moment.