INTRODUCTION ON ORACLE

ORACLE

Oracle is a relational database which is used to store data permanently in secondary storage devices. We can operate Oracle database by using following languages. These are -

• Non Procedural Language (SQL).
• Procedural Language (PL/SQL).
• Dynamic SQL.

All organization stores some type of data.

DATA

It is a collection of raw facts. Example-

• Student Marks
• Customer Names

INFORMATION

Information is nothing but meaningful data or processed data. When ever we are processing data through which we achieve meaningful results is called as Information. Example -

• Student Marksheet.
• Invoice of a customer.

DATASTORE

It is a place where we can store data or information. Organization uses following database mechanism-

1. Books & Papers.
2. Flatfiles.
3. Database.

FLAT-FILES

This is a traditional approach which is used to store data in individual unrelated files are called flatfiles.

• Disadvantages

1. Data retrieval : If you want to fetch data from flat-files then we must develop application programs in high level languages,whereas, in databases we are fetching data from secondary storage devices by using SQL language.
2. Data redundancy : In flat-files sometimes we are maintaining multiple copies of the same data in different locations. This data is also called as duplicate or redundant data. In flat-files whenever we are modifying these data in one file then this modification is never affected in another file. This is called Inconsistency.
3. Data integrity : Integrity means to maintain proper data. In databases we are maintaining proper data by using "constraints", whereas we are maintaining proper data in files by using application programs in high level languages.
4. Data security : Data stored in flatfiles cannot be secured because flatfiles doesn't provides security mechanism whereas databases provides "role base" security.
5. Data indexing : For retrieving data very fast, then databases provides "indexing mechanism" whereas flat-files doesn't provides any "indexing mechanism".

Organizations suffering from flat-files mechanism to store data in secondary storage devices. That's why organizations introduce special software called DBMS software which is used to store data efficiently in secondary devices.

DBMS

Database Management System. It is a collection of programs (software) written to manage database. Example of DBMS software - Oracle, Teradata, SQL Server, MySQL, SqlLite, Db2, Sybase, Informix......

In flat-file approach every application program in the organization maintain its own file separate from other application program.

Whenever we are installing DBMS software then automatically some place is allocated in Hard disk, this is called physical database, and also user interface is automatically created. Through this user interface we can directly interact with the database, and also through the application programs indirectly with the database.

DATABASE

It is a structured collection of inter-related data or organized collection of inter-related data used in the application programs in the organization. Every database having two types of structures. These are - 

• Logical Structure : A structure which is not visible in operating system is called logical structure. In Oracle logical structure contains - tables, views, sequences.....
• Physical Structure : A structure which is visible in operating system is called physical structure. Physical structure is handled by "Database Administrators" only.

DBMS ARCHITECTURE

ANSI has established 3 level architecture for DBMS. This architecture is also called as ANSI / SPARC (Standard Planning and Requirement Committee) architecture. Main objective of DBMS architecture is to separate users view of the database from the way physical;y data is stored in database. DBMS architecture having 3 levels - 

1. Conceptual Level
2. External Level
3. Internal Level

These 3 level architecture provides data independence.

DATA INDEPENDENCE

Upper levels are unaffected by change in the lower levels is called Data Independence. All databases having two types of data independence. These are -

1.  Logical Data Independence : Changes to the conceptual level do not require changes to the external level is called logical data independence. Example : Adding a new wntity in conceptual level should not affect in external level.
2. Physical Data Independence : Changes to the internal level do not require changes to the conceptual level is called physical data independence. Example : Adding a new entity in internal level should not affect in conceptual level.

CONCEPTUAL LEVEL

Conceptual level defines logical structure of the database. Conceptual level does not define how data is physically stored in database. It defines what type of data can be stored in database by specifying data-type and size, and also it defines what type of data cannot be stored in database by specifying constraints.

EXTERNAL LEVEL

External level defines individual users view of the database. Generally in databases some data is confidential that's why data security point of view, Database Administrator create views from the tables and then only those views given to the number of users. Then only users allow to access portion of the data from conceptual level.

INTERNAL LEVEL

Internal level defines how the data is physically stored in database. In all database DBA only handle internal level.

DATA MODEL

How data is represented at conceptual level is defined by means of data model. In the history of database design 3 data models have been in used. These are -

1. Hierarchical Data Model
2. Network Data Model
3. Relational Data Model

HIERARCHICAL DATA MODEL

In this model organizes tree like structure. In this data model also data is represented in the format of records. In this data model record type is also same as type in relational data model. In this model parent-child records relationship is implemented based on one-to-many relationships. Based on one-to-many relationships in this data model products having more duplicate data., because here always child segments are repeated and also this data model products retrieve data very slowly from the database because here always database servers searching data from root node onward. In 1960 IBM introduced IMS (Information Management System) product based on hierarchical data model. If we want to operate hierarchical data model products then we are using procedural language.

Example - Hierarchical Data Model

Example - Relational Model

NETWORK MODEL

In 1970 CODASYL ( Conference on Data System Language ) committee introduced Network Data model. In this data model also data is represented in the format of records and also record type is also same as table in relational data model. In this data model parent-child record relationships is implemented based on many-to-many relationships. That's why this data model products does not have more duplicates data because here child segments/records are never repeated. In 1970 IBM introduced IDMS (Information Data Management System) product based on network data model. If we want to operate network data model products also then we are using procedural language.

RELATIONAL DATA MODEL

In 1970 E.F.Codd introduced relational data model. In relational data model storing data in 2D tables. This tables also having records, and now also established relationship between records by using keys. Relational data model mainly consist of 3 components. These are :

1. Collection of Database Objects : Example - tables, views, indexes...
2. Collection of Operators : < , > , U , etc
3. Set of integrity rules.

Example of Relational Data Model Products - Oracle, MySQL, db2, Teradata, SqlLite, Sybase, Sql Server, Informix..

HISTORY

In 1977 Larry Ellison, Bob Miner, Ed Oates started new company named "Software Development Laboratories (SDL)". In 1977 "Scott" first employee was hired at SDL. In 1978 SDL company released "Oracle 1.0" (this version was never released officially). In 1979 SDL company name changed into RSI (Relational Software Inc.)