Found 115 Articles for RDBMS

Edgar F Codd was a Computer Scientist who invented the Relational model for Database management. He is also credited with creating the foundation for relational databases as well as relational database management systems.Codd’s twelve rules define the characteristics required by a database management system to be considered relational i.e  a relational database management system.Rule 0: Foundation ruleFor any system to be qualified as a relational database management system, it should manage its data using its relational capability.Rule 1: Information ruleAll information (including metadata) is represented in tables using rows and columns. The rows and columns have to be strictly unordered.Rule ... Read More

GeneralizationGeneralization is a process of generalizing an entity which contains generalized attributes or properties of generalized entities. The entity that is created will contain the common features. Generalization is a Bottom up process.We can have three sub entities as Car, Truck, Motorcycle and these three  entities can be generalized into one general super class as Vehicle.It is a form of abstraction that specifies two or more entities (sub class) having common characters that can be generalized into one single entity (super class) at higher level hiding all the differences.SpecializationSpecialization is a process of identifying subsets of an entity that shares ... Read More

A given ER model can be converted into Relational model. A Relational model includes Relations, Tuples, Attributes, Keys, and Foreign keys.Relation is a table made from tuples.A Tuple is a row of data.An Attribute is a characteristic of the relation.There is a direct mapping between ER model and Relational model.Consider the following example −Rules of converting ER model to Relational Model-Entity type is converted to a Relation table.1:1 or 1: N relationship type is converted to foreign key.M: N relationship type is converted to a relation with two foreign key.Simple attribute converted to an attribute.Value set converted to a domain.Key ... Read More

EER is a high-level data model that incorporates the extensions to the original ER model. Enhanced ERD are high level models that represent the requirements and complexities of complex database.In addition to ER model concepts EE-R includes −Subclasses and Super classes.Specialization and Generalization.Category or union type.Aggregation.These concepts are used to create EE-R diagrams.Subclasses and Super classSuper class is an entity that can be divided into further subtype.For example − consider Shape super class.Super class shape has sub groups: Triangle, Square and Circle.Sub classes are the group of entities with some unique attributes. Sub class inherits the properties and attributes from ... Read More

SQL (Structured Query Language) is a specialized programming language which is standardized to be used for managing relational databases and performing various operations on the data. There are various uses of SQL which includes modifying database table and index structures; adding, updating and deleting rows of data; and retrieving various subsets of information from a database for transaction processing and analytics applications. There are specialized queries and operations which operates in the form of commands and commonly known as SQL statements like select, add, insert, update, delete, create, alter and truncate.SQL became standard programming language for relational databases after they ... Read More

A hierarchical model represents the data in a tree-like structure in which there is a single parent for each record. To maintain order there is a sort field which keeps sibling nodes into a recorded manner. These types of models are designed basically for the early mainframe database management systems, like the Information Management System (IMS) by IBM.This model structure allows the one-to-one and a one-to-many relationship between two/ various types of data. This structure is very helpful in describing many relationships in the real world; table of contents, any nested and sorted information.The hierarchical structure is used as the ... Read More

In a "product sales" database, a product may have optional supplementary information such as image, more description and comment. Keeping them inside the Products table results in many empty spaces (in those records without these optional data). Furthermore, these large data may degrade the performance of the database.Instead, we can create another table (say ProductDetails, ProductLines or ProductExtras) to store the optional data. A record will only be created for those products with optional data. The two tables, Products and ProductDetails, exhibit a one-to-one relationship. That is, for every row in the parent table, there is at most one row ... Read More

In a "product sales" database, a customer's order may contain one or more products; and a product can appear in many orders. In a "bookstore" database, a book is written by one or more authors; while an author may write zero or more books. This kind of relationship is known as many-to-many.Let's illustrate with a "product sales" database. We begin with two tables: Products and Orders. The table products contain information about the products (such as name, description and quantityInStock) with productID as its primary key. The table orders contain customer's orders (customerID, dateOrdered, dateRequired and status). Again, we cannot ... Read More

In a "class roster" database, a teacher may teach zero or more classes, while a class is taught by one (and only one) teacher. In a "company" database, a manager manages zero or more employees, while an employee is managed by one (and only one) manager. In a "product sales" database, a customer may place many orders; while an order is placed by one particular customer. This kind of relationship is known as one-to-many.The one-to-many relationship cannot be represented in a single table. For example, in a "class roster" database, we may begin with a table called Teachers, which stores ... Read More

Relational database design (RDD) models’ information and data into a set of tables with rows and columns. Each row of a relation/table represents a record, and each column represents an attribute of data. The Structured Query Language (SQL) is used to manipulate relational databases. The design of a relational database is composed of four stages, where the data are modeled into a set of related tables. The stages are −Define relations/attributesDefine primary keysDefine relationshipsNormalizationRelational databases differ from other databases in their approach to organizing data and performing transactions. In an RDD, the data are organized into tables and all types ... Read More