There is no standard for representing data objects in ER diagrams. Each modeling methodology uses its own notation. [Read more…] about E-R NOTATION
What is the Basic Construction of E-R Modeling?
In Entity-Relationship model a database is modeled as a collection of entities and relationship among entities. The ER model views the real world as a construct of entities and association between entities. [Read more…] about What is the Basic Construction of E-R Modeling?
What is ER-Model?Advantages and Disadvantages of E-R Model.
There are two techniques used for the purpose of data base designing from the system requirements. These are:
• Top down Approach known as Entity-Relationship Modeling
• Bottom Up approach known as Normalization. [Read more…] about What is ER-Model?Advantages and Disadvantages of E-R Model.
Relational Model
Relational model stores data in the form of tables. This concept purposed by Dr. E.F. Codd, a researcher of IBM in the year 1960s. The relational model consists of three major components: [Read more…] about Relational Model
Network Model
The Network model replaces the hierarchical tree with a graph thus allowing more general connections among the nodes. The main difference of the network model from the hierarchical model, is its ability to handle many to many (N:N) relations. In other words, it allows a record to have more than one parent. Suppose an employee works for two departments. The strict hierarchical arrangement is not possible here and the tree becomes a more generalized graph – a network. The network model was evolved to specifically handle non-hierarchical relationships. As shown below data can belong to more than one parent. Note that there are lateral connections as well as top-down connections. A network structure thus allows 1:1 (one: one), l: M (one: many), M: M (many: many) relationships among entities. [Read more…] about Network Model
What are Data Models? Type of Data Models.
A model is a representation of reality, ‘real world’ objects and events, associations. It is an abstraction that concentrates on the essential, inherent aspects an organization and ignores the accidental properties. A data model represents the organization itself. It should provide the basic concepts and notations that will allow database designers and end users unambiguously and accurately to communicate their understanding of the organizational data. [Read more…] about What are Data Models? Type of Data Models.
Type of Database System
The DBMS can be classified according to the number of users and the database site locations. These are: [Read more…] about Type of Database System
What are the Functions and Service of DBMS
A DBMS performs several important functions that guarantee integrity and consistency of data in the database. Most of these functions are transparent to end-users. There are the following important functions and services provided by a DBMS: [Read more…] about What are the Functions and Service of DBMS
What are the Components of DBMS?
A typical structure of a DBMS with its components and relationships between them is show. The DBMS software is partitioned into several modules. Each module or component is assigned a specific operation to perform. Some of the functions of the DBMS are supported by operating systems (OS) to provide basic services and DBMS is built on top of it. The physical data and system catalog are stored on a physical disk. Access to the disk is controlled primarily by as, which schedules disk input/output. Therefore, while designing a DBMS its interface with the as must be taken into account. [Read more…] about What are the Components of DBMS?
Database Languages
A DBMS must provide appropriate languages and interfaces for each category of users to express database queries and updates. Database Languages are used to create and maintain database on computer. There are large numbers of database languages like Oracle, MySQL, MS Access, dBase, FoxPro etc. SQL statements commonly used in Oracle and MS Access can be categorized as data definition language (DDL), data control language (DCL) and data manipulation language (DML). [Read more…] about Database Languages
What is Metadata OR Data Dictionary?
A metadata (also called the data dictionary) is the data about the data. It is the self describing nature of the database that provides program-data independence. It is also called as the System Catalog. It holds the following information about each data element in the databases. [Read more…] about What is Metadata OR Data Dictionary?
What is the role of DBA, Data Manager, File Manager, and Disk Manager?
Functions of Data Base Administrator
Data Base Administrator (DBA) is a person or group in charge for implementing DBMS in an organization. Database Administrator’s job requires a high degree of technical expertise and the ability to understand and interpret management requirements at a senior level. In practice the DBA may consist of team of people rather than just one person. [Read more…] about What is the role of DBA, Data Manager, File Manager, and Disk Manager?
What is the Procedure for Database Access?
Any access to the stored data is done by the data manager. A user’s request for data is-received by the data manager, which detern1ines the physical record required. The decision as 10 which physical record is needed may require some preliminary consultation of the database and/or the data dictionary prior to the access of the actual data itself. [Read more…] about What is the Procedure for Database Access?
What is Data Independence of DBMS?
A major objective for three-level architecture is to provide data independence, which means that upper levels are unaffected by changes in lower levels. [Read more…] about What is Data Independence of DBMS?
What are INTANCES, SCHEMAS AND SUBSCHEMA in DBMS?
Database changes over time when information is inserted or deleted. The collection of information stored in the database at a particular moment is called an instance of the database. The overall design of the database is called the database schema. [Read more…] about What are INTANCES, SCHEMAS AND SUBSCHEMA in DBMS?
What is DBMS? Advantages and Disadvantages of DBMS.
DBMS A database management system is the software system that allows users to define, create and maintain a database and provides controlled access to the data. [Read more…] about What is DBMS? Advantages and Disadvantages of DBMS.
Database Approach
In order to remove all limitations of the File Based Approach, a new approach was required that must be more effective known as Database approach. [Read more…] about Database Approach
Traditional File Processing System
File processing systems was an early attempt to computerize the manual filing system that we are all familiar with. A file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. File systems may use a storage device such as a hard disk or CD-ROM and involve maintaining the physical location of the files. [Read more…] about Traditional File Processing System
Database Model
Hierarchical Database Model
Hierarchical Database model is one of the oldest database models, dating from late 1950s. One of the first hierarchical databases Information Management System (IMS) was developed jointly by North American Rockwell Company and IBM. This model is like a structure of a tree with the records forming the nodes and fields forming the branches of the tree. [Read more…] about Database Model
What is a Database Users
The Database Users fall into several categories:
• Application Programmers are computer professionals interacting with the system through DML calls embedded in a program written in a host language (e.g. C, PL/1, Pascal): These programs are called Application Programs. The DML Precompiled converts DML calls (prefaced by a special character like $, #, etc.) to normal procedure calls in a host language. [Read more…] about What is a Database Users
Database System Structure
Database System Structure are partitioned into modules for different functions. Some functions (e.g. file systems) may be provided by the operating system. Components include: [Read more…] about Database System Structure
Advantages of Database
There are four basic components of Database Management System:
(i) Data: Raw facts which we want to feed in the computer. [Read more…] about Advantages of Database
What is DBA?
A Database Administrator, Database Analyst or Database Developer is the person responsible for managing the information within an organization. As most companies continue to experience inevitable growth of their databases, these positions are probably the most solid within the IT industry. [Read more…] about What is DBA?
What are the Difference Between DDL, DML and DCL Commands?
SQL statements are divided into two major categories: data definition language (DDL) and data manipulation language (DML). [Read more…] about What are the Difference Between DDL, DML and DCL Commands?
what is a Database Concurrency Control
When multiple transactions are trying to access the same sharable resource, there could arise many problems if the access control is not done properly. There are some important mechanisms to which access control can be maintained. Earlier we talked about theoretical concepts like serializability, but the practical concept of this can be implemented by using Locks and Timestamps. [Read more…] about what is a Database Concurrency Control
What is a Database Server
What is a database server? It is similar to data warehouse where the website store or maintain their data and information. A Database Server is a computer in a LAN that is dedicated to database storage and retrieval. The database server holds the Database Management System (DBMS) and the databases. Upon requests from the client machines, it searches the database for selected records and passes them back over the network. [Read more…] about What is a Database Server
What is a Database View
What is a Database View, A view can join information from several tables together, or we can say that Views are useful for Hiding unwanted information for example adding the ename field to the Order information. Database View is a subset of the database sorted and displayed in a particular way. A database view displays one or more database records on the same page. A view can display some or all of the database fields. [Read more…] about What is a Database View
What is a Database Instance
The environment of database is said to be instance. A database instance or an ‘instance’ is made up of the background processes needed by the database software. These processes usually include a process monitor, session monitor, lock monitor, etc. They will vary from database vendor to database vendor. [Read more…] about What is a Database Instance
What is a Database Object
A database object in a relational database is a data structure used to either store or reference data. The most common object that most people interact with is the table. Other objects are indexes, stored procedures, sequences, views and many more. [Read more…] about What is a Database Object
What is a Database Schema
A database instance controls 0 or more databases. A database contains 0 or more database application schemas. A database application schema is the set of database objects that apply to a specific application. These objects are relational in nature, and are related to each other, within a database to serve a specific functionality. [Read more…] about What is a Database Schema