Relational Database management Models-MCA.pptx
- 2. Data Model • Data Model is the modeling of the data description, data semantics, and consistency constraints of the data. • It provides the conceptual tools for describing the design of a database at each level of data abstraction. • Therefore, there are following four data models used for understanding the structure of the database:
- 4. • 1) Relational Data Model: This type of model designs the data in the form of rows and columns within a table. • Thus, a relational model uses tables for representing data and in-between relationships. Tables are also called relations. • This model was initially described by Edgar F. Codd, in 1969. • The relational data model is the widely used model which is primarily used by commercial data processing applications.
- 6. • Entity-Relationship Data Model: An ER model is the logical representation of data as objects and relationships among them. • These objects are known as entities, and relationship is an association among these entities. • This model was designed by Peter Chen and published in 1976 papers. • It was widely used in database designing. A set of attributes describe the entities. • For example, student_name, student_id describes the 'student' entity. • A set of the same type of entities is known as an 'Entity set', and the set of the same type of relationships is known as 'relationship set'.
- 8. • Object-based Data Model: An extension of the ER model with notions of functions, encapsulation, and object identity, as well. • This model supports a rich type system that includes structured and collection types. • Thus, in 1980s, various database systems following the object-oriented approach were developed. • Here, the objects are nothing but the data carrying its properties.
- 9. • 4) Semistructured Data Model: This type of data model is different from the other three data models (explained above). • The semistructured data model allows the data specifications at places where the individual data items of the same type may have different attributes sets. • The Extensible Markup Language, also known as XML, is widely used for representing the semistructured data. • Although XML was initially designed for including the markup information to the text document, it gains importance because of its application in the exchange of data.
- 10. Data model Schema and Instance • The data which is stored in the database at a particular moment of time is called an instance of the database. • The overall design of a database is called schema. • A database schema is the skeleton structure of the database. It represents the logical view of the entire database. • A schema contains schema objects like table, foreign key, primary key, views, columns, data types, stored procedure, etc.
- 12. • A schema diagram can display only some aspects of a schema like the name of record type, data type, and constraints. • Other aspects can't be specified through the schema diagram. • For example, the given figure neither show the data type of each data item nor the relationship among various files.
- 13. • A database schema can be represented by using the visual diagram. That diagram shows the database objects and relationship with each other. • A database schema is designed by the database designers to help programmers whose software will interact with the database. The process of database creation is called data modeling.
- 14. • In the database, actual data changes quite frequently. • For example, in the given figure, the database changes whenever we add a new grade or add a student. • The data at a particular moment of time is called the instance of the database.
- 15. • Data Independence • Data independence can be explained using the three-schema architecture. • Data independence refers characteristic of being able to modify the schema at one level of the database system without altering the schema at the next higher level.
- 16. • There are two types of data independence: • 1. Logical Data Independence • Logical data independence refers characteristic of being able to change the conceptual schema without having to change the external schema. • Logical data independence is used to separate the external level from the conceptual view. • If we do any changes in the conceptual view of the data, then the user view of the data would not be affected. • Logical data independence occurs at the user interface level.
- 17. • Physical Data Independence • Physical data independence can be defined as the capacity to change the internal schema without having to change the conceptual schema. • If we do any changes in the storage size of the database system server, then the Conceptual structure of the database will not be affected. • Physical data independence is used to separate conceptual levels from the internal levels. • Physical data independence occurs at the logical interface level.
- 19. • Database Language • A DBMS has appropriate languages and interfaces to express database queries and updates. • Database languages can be used to read, store and update the data in the database.
- 21. • Data Definition Language • DDL stands for Data Definition Language. It is used to define database structure or pattern. • It is used to create schema, tables, indexes, constraints, etc. in the database. • Using the DDL statements, you can create the skeleton of the database. • Data definition language is used to store the information of metadata like the number of tables and schemas, their names, indexes, columns in each table, constraints, etc.
- 22. • Here are some tasks that come under DDL: • Create: It is used to create objects in the database. • Alter: It is used to alter the structure of the database. • Drop: It is used to delete objects from the database. • Truncate: It is used to remove all records from a table. • Rename: It is used to rename an object. • Comment: It is used to comment on the data dictionary.
- 23. • Data Manipulation Language • DML stands for Data Manipulation Language. It is used for accessing and manipulating data in a database. It handles user requests. • Here are some tasks that come under DML:
- 24. • Select: It is used to retrieve data from a database. • Insert: It is used to insert data into a table. • Update: It is used to update existing data within a table. • Delete: It is used to delete all records from a table. • Merge: It performs UPSERT operation, i.e., insert or update operations. • Call: It is used to call a structured query language or a Java subprogram. • Explain Plan: It has the parameter of explaining data. • Lock Table: It controls concurrency.
- 25. • Data Control Language • DCL stands for Data Control Language. It is used to retrieve the stored or saved data. • The DCL execution is transactional. It also has rollback parameters. • (But in Oracle database, the execution of data control language does not have the feature of rolling back.)
- 26. • Here are some tasks that come under DCL: • Grant: It is used to give user access privileges to a database. • Revoke: It is used to take back permissions from the user. • There are the following operations which have the authorization of Revoke: • CONNECT, INSERT, USAGE, EXECUTE, DELETE, UPDATE and SELECT.
- 27. • Transaction Control Language • TCL is used to run the changes made by the DML statement. TCL can be grouped into a logical transaction. • Here are some tasks that come under TCL: • Commit: It is used to save the transaction on the database. • Rollback: It is used to restore the database to original since the last Commit.
- 29. ER-DIAGRAM • ER model • ER model stands for an Entity-Relationship model. It is a high-level data model. This model is used to define the data elements and relationship for a specified system. • It develops a conceptual design for the database. It also develops a very simple and easy to design view of data. • In ER modeling, the database structure is portrayed as a diagram called an entity-relationship diagram.
- 30. • For example, • Suppose we design a school database. • In this database, the student will be an entity with attributes like address, name, id, age, etc. • The address can be another entity with attributes like city, street name, pin code, etc and there will be a relationship between them.
- 35. • 1. Entity: • An entity may be any object, class, person or place. In the ER diagram, an entity can be represented as rectangles. • Consider an organization as an example- manager, product, employee, department etc. can be taken as an entity.
- 39. • An entity that depends on another entity called a weak entity. • The weak entity doesn't contain any key attribute of its own. • The weak entity is represented by a double rectangle.
- 41. • 2. Attribute • The attribute is used to describe the property of an entity. Eclipse is used to represent an attribute. • For example, id, age, contact number, name, etc. can be attributes of a student.
- 43. • a. Key Attribute • The key attribute is used to represent the main characteristics of an entity. • It represents a primary key. • The key attribute is represented by an ellipse with the text underlined.
- 45. • . Composite Attribute • An attribute that composed of many other attributes is known as a composite attribute. • The composite attribute is represented by an ellipse, and those ellipses are connected with an ellipse.
- 47. • An attribute can have more than one value. These attributes are known as a multivalued attribute. The double oval is used to represent multivalued attribute. • For example, a student can have more than one phone number.
- 49. • d. Derived Attribute • An attribute that can be derived from other attribute is known as a derived attribute. It can be represented by a dashed ellipse. • For example, A person's age changes over time and can be derived from another attribute like Date of birth.
- 50. • 3. Relationship • A relationship is used to describe the relation between entities. Diamond or rhombus is used to represent the relationship.
- 52. • b. One-to-many relationship • When only one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then this is known as a one-to-many relationship. • For example, Scientist can invent many inventions, but the invention is done by the only specific scientist.