by Dinesh Thakur Category: DBMS & RDBMS

An early proposal for a standard terminology and general architecture for database systems was produced in 1971 by the DBTG (Data Base Task Group) appointed by the Conference on Data Systems and Languages (CODASYL, 1971). The DBTG recognized the need for a two level approach with a system view called the schema and user views called subschema. The American National Standards Institute (ANSI) Standards Planning and Requirements Committee (SPARC) produced a similar terminology mid architecture in 1975 (ANSI 1975). ANSI-SPARC recognized the need for a three level approach with a system catalog.



 
by Dinesh Thakur Category: DBMS & RDBMS

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).



 
by Dinesh Thakur Category: DBMS & RDBMS

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:

 
by Dinesh Thakur Category: DBMS & RDBMS

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

The Database is a shared collection of logically related data, designed to meet the information needs of an organization. A database is a computer based record keeping system whose over all purpose is to record and maintains information. The database is a single, large repository of data, which can be used simultaneously by many departments and users. Instead of disconnected files with redundant data, all data items are integrated with a minimum amount of duplication.



 
by Dinesh Thakur Category: DBMS & RDBMS

SQL statements are divided into two major categories: data definition language (DDL) and data manipulation language (DML).

Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:



 
by Dinesh Thakur Category: DBMS & RDBMS

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.



 
by Dinesh Thakur Category: DBMS & RDBMS

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:



 
by Dinesh Thakur Category: DBMS & RDBMS

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.



 
by Dinesh Thakur Category: DBMS & RDBMS

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.

 
by Dinesh Thakur Category: DBMS & RDBMS

Relation schema: A set of attributes is called a relation schema (or relation scheme). A relation schema is also known as table schema (or table scheme). A relation schema can be thought of as the basic information describing a table or relation. It is the logical definition of a table. Relation schema defines what the name of the table is. This includes a set of column names, the data types associated with each column.



 

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.



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