Data Independence

Data Independence is the property of DBMS by virtue of which it has the capacity to change the schema at one level of a database system without having to change the schema at the next higher level.

Types of data Independence

• There are two types of data independence

1. Physical data independence.

2. Logical data independence.

1. Physical data independence

• Physical data independence refers to the immunity of the conceptual schema to the changes of the internal schema.

OR

Physical data independence is the capacity to change the internal schema without having any change to the conceptual schema.

2. Logical data independence

• Logical data independence refers to the immunity of the external schemas to changes in the conceptual schema.

OR

Logical data independence is the capacity to change the conceptual schema without having to change the external schema or the application schema.

Database Languages:

• Database Languages can broadly be divided into three types:

1. DDL (Data Definition languages)

2. DML (Data Manipulation Languages)

3. TCL (Transaction Control Languages)

4. Fourth-Generation Languages(4GLs)

1. DDL (Data Definition Language):

• DDL is a language that allows the DBA or user to describe and name the entities, attributes and relationships required for the application, together with any associated integrity and security constraints.

• DDL is used to specify the conceptual schema only.

• SDL (Storage Definition Language) is used to specify the internal schema.

• VDL (View Definition Language) is used to specify the view level or the external level schema.

2. DML (Data Definition Language)

• DML is the language used to manipulate or to maintain the database.

• DML further has been divided into two types

a. Procedural data manipulation language.

b. Non procedural data manipulation

language.

a. Procedural DML

• Procedural DML is a language that allows the users to tell the system what data is needed and exactly how to retrieve the data.

• Procedural DML explains only what to perform along with how to perform.

b. Non-Procedural DML

• Non-Procedural DML is a language that allows the users to state what data is needed rather than how it is to be retrived.

3. TCL (Transaction Control Lang)

• TCL is a language which helps the users to make different transactions with the database.

4. Fourth Generation Languages (4GLs)

• 4GL is a non-procedural language where the user needs to define what is to be done not how to be done.

• This consists of presentation languages such as query languages and report generators.

• This language encompass specialty languages such as spreadsheets and database languages.

• This also consists of application generators that define, insert, update, and retrieve data from the database to build applications.

• This also provides very high level languages that are used to generate application code.

Different types of 4GLs:

• The different types of 4GLs are

1. Forms Generators.

2. Reports Generators.

3. Graphics Generators.

4. Application Generators.

1.Forms Generators.

• The form generator is an interactive facility for rapidly creating data input and display layouts for screen forms.

• The screen generator allows the users to define what the screen is to look like, what information is to be displayed and where on the screen it is to be displayed.

2. Report Generators.

• A report generator is the facility for creating reports from data stored in the database.

• There are two types of report generators:a. Language-Orientedb. Visually oriented

• In case of language-Oriented report generator the user need to enter a command in a sublanguage to define what data is to be included in the report and how the report is to be laid out.

• In case of Visually oriented report generator the user need to use a facility similar to a forms generator to define the same information.

3. Graphics Generators:

• The Graphics generator is a facility to retrieve data from the database and display the data as a graph showing trends and relationships in the data.

• It allows the users to create bar charts, pie charts, line charts etc.

4. Application generators:

• An application generator is a facility for producing a program that interfaces with the database.

• Application generator typically consist of pre-written modules that comprise fundamental functions that most programs use.

DBMS Interfaces:

• The medium by use the users can interface with the data base is called as the DBMS interface.

• The different types DBMS interfaces are1. Menu-Based interface.2. Forms-Based interface.3.Graphical User interface (GUI).4.Natural Language interface.5. Interface for parametric end users.6. Interface for DBA

1. Menu-Based Interface:

• These interfaces present the users with lists of options called menus that lead the user through the formulation of a request.

2. Forms-Based Interfaces:

• A forms-Based interface displays a form to each user. Users can fill out all the forms to insert a new data or can fill out only certain entries in case of data retrieval.

• DBMS s have forms specification languages to support Forms-Based interfaces.

3. Graphical User Interface (GUI)

• A GUI typically displays a schema to the users in diagrammatic form and the users are to specify a query by manipulating the diagram.

• In many of the cases GUIs use both menus and forms as well as pointing devices.

4. Natural Language Interface:

• These interfaces accept requests written in common languages generally in english.

5. Interface for Parametric End Users:

• Special type of interfaces are supporting the parametric type of end users.

• This type of interfaces has been created to support canned transactions.

6. Interface for DBA:

• A very special type of interfaces are there to assist the DBA in its work.

• This type of interface helps the DBA to include commands for creating accounts, setting system parameters, Granting authorization, changing a schema etc.