Database Fundamentals must be prepared to all the computer professionals and users. If you lack in their actual meaning, you would always find an uneasiness and uncomfort when these concepts come to you. This article is targeted to a novice and expert both, sothat novice can prepare and an expert can revise things as well. With all these thoughts, moving forward to Database Fundamentals.
[ 1 ] Entity and Entity Relationships
Entity :
An Entity is place, object or thing for which we can collect information.
Such as Student is an Entity and we can collection informations like Name, Phone and Address. Here, Name, Phone and Address are the Attributes of entity 'student'.
Entity Relationship Diagram :
Also called as E-R Diagram. E-R Diagram is the graphical depiction of the entity, its attribute and relationship between entities.
[ 2 ] Data and Database
Data :
Data are the single unit of an information.
Such as if name of an employee is 'Som Dutt', then 'Som Dutt' is a data. His telephone no. is '+9109880959706', then, this is also a data. The value of the attribute of any entity can be said as data.
So, Data are the known facts that can be recorded and have their implicit meaning. e.g. name, telephone, address etc.
Data is a plural and 'Datum' is the singular form of the data.
Information :
When the set of data are collected together in a meaningful manner, an information is generated.
Such as if we take example of an employee 'Som Dutt'. The Name is 'Som Dutt' , Telephone no. is '+9109880959706' , designation is 'DBA'. So, if we collectively analyze these, we get information that Som Dutt is an employee with telephone no. 898898 and he is designated as DBA.
So, When the some set of data are collected together, information get produced. The information is not for computer, this is just for humans only.
Database :
Database is the collection of related data.
Database is logically coherent collection of data with some inherent meaning. A random assortment of data can not be said as database. Such as a Telephone Diary is also a database, but, if it is randomly stored then, it can not be said as database. Database can be generated manually or in computerized manner. The Library catalog is also a database.
[ 2 ] Database Management System (DBMS) :
Database Management System is the collection of programs and tools that enables users to create and maintain the database.
A DBMS is also a general purpose software system that facilitates the process of defining, constructing and manipulating databases for various applications.
Characteristics of Database Management System :
[1] Self Describing
[2] Insulation from Programs and Data Abstraction
[3] Support of Multiple views to Database.
[ 3 ] Advantages of DBMS:
1- Controlling Redundancy :
There are provisions in all database models that redundant storage of the data can be avoided.
2- Security Over Unauthorized Access :
This is the feature found in the database that without proper login, no one can modify or store database. The security can not be achieved with the flat file (Sequential) approach.
3- Providing Persistent Storage for Database Objects :
Database can be used as the persistent storage of Program objects, Database and Database structures. This meant that a complex object of programming languages can be stored in the database. This gives more flexibility and compatibility of database over the programming languages.
4- Permitting Inferencing and Actions using Rules :
Inferencing is the method for defining deducing rules for inferencing new information from stored database. Such database are called as Deducible Database. In other words, there must be some methods to provide information by logical implementation on the stored database.
6- Allowing Multiple User Interface :
DBMS has the capability to provide concurrent execution of various parts of the database. In this approach, Deadlock and other anomalies are also handled by the DBMS.
5- Backup and Recovery :
Database Management Systems have proper mechanism to Backup the whole database and recover when any disaster comes to picture. There are methods for Disaster Recovery in all DBMS.
[ 4 ] Data Models :
A data model is the set of conceptual tools for describing data, their relation, semantics and consistency constraints. There are following data models-
[1] Hierarchical Model
[2] Network Model
[3] Relational Model
[4] Object Relational Model
Describing all of these would be out of context. You should know that with all these, Relational Model is famous one. Newer implementation of DBMS do follow Object Oriented Model. Such as Oracle, Sybase and SQL Server.
[ 6 ] Logical and Physical Data Independence :
Data Independence is the quality of DBMS that ensure the capability to change the database in a manner that the change in one level does not affect the other level. Such as change in the physical storage (Internal Level) does not affect the database structure (Conceptual Level).
[1] Logical Data Independence:
Capability to change the Logical structure without changing the external and internal schema of the database.
[2]Physical Data Independence:
Capability to change the Physical schema without any change in the conceptual schema of the database.
[ 7 ] Database Languages :
There are following database languages-
[1] DDL (Data Definition Language)
[2] DML (Data Manipulation Language)
[3] DCL (Data Control Language)
[1] DDL (Data Definition Language)
This is the language concerned with the creation of database structure and schema related with this. This language is concerned with the definition of the whole database architecture. DDL is used to define and manage all the objects in an database. Such as creating Databases, creating security objects that define the whole database.
[2] DML (Data Manipulation Language)
Insertion, Update , Delete and Selection are the activities concerned with the database manipulation language. DML is used to Select, Insert, Update, and Delete data in the objects defined using DDL.
[3] DCL ( Database Control Language)
Database control language is concerned with the consistency maintaining, authorizing access and other control over the database.
There are some other languages which must be known. These are -
VDL (View Definition Language) : Providing means to view the conceptual schema of database for external level of three level schema.
SDL (Storage Definition Language) : Providing means to change or modify the internal schema of the database.
[ 8 ] Relational Database :
The Relation database model is based upon the conception of implementing the database with the Mathematical Set Theory. In this model, data is collection of tables called Relation in the set theory. The Tabular representation of data contains rows and columns in which rows represent set of attributes of individual entity and the columns represent the attribute of entity.
A model is also said as Relational Database Model, if it follows complete set of Rules defined by Dr. E.F. Codd. There are 12 Rules of Dr. Codd. In all of them, only Oracle is supposed to follow nearly all of them. But, the best in performance is Sybase which is more easier to configure that of Oracle.
SQL :
SQL is actually Structured Query Language. This is pronunciated as 'sequel', but 'Ess-Que-El' is also correct.
SQL is based on the Relational Model. Nearly all the database implementation in the world are in Relational Model. DBase, Fox-Pro, MS Access, Sybase ,SQL Server, Oracle, Ingres, DB2 are the famous implementation of Relational Model. But these are also kept in the Category of Object Relational Model.
SUMMARY
Data : Data are the known facts that can be recorded and has the implicit meaning.
Database : Database is the collection of related data.
Database Management System : DBMS is the collection of programs and tools that enable user to create and maintain data.
Redundancy : The storage of the same data in various location in the database is redundancy.
|
