What is Schema , What are its uses in DBMS ?

STRUCTURE OF DBMS:-

                                         DBMS (Database Management System) acts as an interface between the user and the and retrieval) on the database. The components of DBMS perform these requested operations On the database and provide necessary data to the users. 

1. DDL Compiler Data Description Languag compiler processes schema definitions Specified in the DDL. It includes metadata information such as the name of the files, data Cms, storage details of each file, mapping information and constraints etc. 
   
   
2. DML Compiler and Query optimizer The DML commands such as insert, update, delete, retrieve from the application program are sent to the DML compiler for comni into object code for database access. The object code is then optimized in the best INTRODUC execute a query by the query optimizer and then send to the data manager.
   
   
3. Data Manager - The Data Manager is the central software component of the DBMSexterna also knows as Database Control System. The main functions of Data Manager are ) Controls DBMS information access that is stored on disk. (ii) Enforces constraints to maintain consistency and integrity of the data. enable descri (iii) Synchronizes the simultaneous operations performed by the concurrent users. (iv) Controls the backup and recovery operations. data DBM (v) Convert operations in user's queries coming from the application programs or 1. 1 combination of DML Compiler and Query optimizer which is known as Query Processor from user's logical view to physical file system. 
   
   
4. Data Dictionary -Data Dictionary is a It contains repository of description of data in the database. exist information required for managing database and its various operations.
   
   
5. Data Files -It contains the data portion of the database. 
   
   
6. Compiled DML -The DML complier converts the high level queries into low level fle access commands known as compiled DML. 
   
   
7. End Users -End users are preliminary computer based users. The function of ena U are only to operate the computer and feed or type the collected information (data) in mcu driven application program and to execute it according to the analyst' requirement. 1n el users are also called Data Entry operators. 
   
   
   

•  SCHEMA AND SUBSCHEMA :-

Schema represents the overall structure or design of the database. It is a framework into hich the values of the data items data fields are fitted. It is important to distinguish aween the description of the database and the database itself. The description of the database is the databasc schema. The schema Is specitied during the database design process dis not expected to change frequently. However the actual data in the database may change foaently. For example: It changes every ime whenever we insert a new record in the database.

              In other words, schema means the overall plan or scheme that describes the records and relationships among them existing at a particular level in the DBMS architecture.

• TYPES OF SCHEMA :-

There are three different types of schema in the database corresponding to each data view of database:

             i) External schema

             ii) Conceptual schema 

             iii) Internal schema

i) External schema: The external view is described by means of a schema called e DBMS external schema that correspond to different views of the data. It specifies different views that re: enable different users of the data to see it in different ways.  

ii) Conceptual schema: The conceptual view is defined by conceptual schema, which describes all the entities, attributes and relationship together with integrity constraints. 

iii) Internal schema: Internal view is defined by internal schema. It describes how the data will be physically stored and accessed, using the facilities provided by a particular DBMS .

 SUBSCHEMA:-

                                Subschema is the subset of schema. It inherits the same property as that of a schema. The subschema refers to user's view of fields that he or she needs from the database. As there exist multiple users, each accessing some portion of the database so there can exist different sub-schemas for a given schema.

             Sub-schemas are mainly used due to the following reasons:

• Sub-schemas provide different views of the data to the user and the programmer, who do not need to know all the data contained in the entire database.
• Sub-schemas enhance security factors and prohibit data compromise.
• Sub-schemas give support to the DBA while assuring data integrity .

DATA INDEPENDENCE:-

                                            Database management system (DBMS) supports the concept or data independence sine functions and res it represents a system for managing data separately from the programs that use the data, The three-level architecture of DBMS provides the concept of data independence, whic means that upper-levels are unaffected by changes to lower-levels. In other words, it allow changes to the structure of a database without requiring application programs or users DBA is organiza DBA databas= make any change in the way they access the data.

Types of Data Independence:-

                               (a) Logical Data Independence: The ability to change the logical or conceptual schem of database without changing the external schema is called logical data independence. Fo example, the addition or removal of an attribute or field to the conceptual schema should b possible without having to change existing external schema or having to re'write existin application programs. data DBA lost th�DBA datab 

                                  (b) Physical Data Independence: The ability to change the physical or internal without schem changing the logical schema is called physical data independence. For example,i change to the internal schema, such as using different storage devices should be without possibk having to change the conceptual or external schemas .

•  DBA (DATABASE ADMINISTRATOR:-

One of the main reasons for using DBMS is to have central control of both the data and the programs that access those data. A person who has such central control over the database system is called a Database Administrator (DBA). 

                        The DBA (Database Administrator) is a single person or a group of persons responsible for implementing the database system with in an organization. DBA is only the guardian of the organization but not the owner of the organization. As bank manager is the DBA of a hank, who takes care about the bank money and not use it. Only DBA can handle the information collected by end user and give the instructions to the application programmer for developing a new program or modifying an existing program. The DBA has following functions and responsibilities regarding database management: 

• DBA is responsible for the design, implementation, maintenance and repair of an organization's database. endence, whie words, it allow ams or users 
•  DBA decides the information contents of the database. He decides the suitable database file structure for arrangement of data. 
•  DBA compiles the whole data in a particular order and sequence. 
•  DBA decides where data can be stored i.e. take decision about the storage structure. DBA decides which access strategy and technique should be used for accessing the data. eptual schema pendence. Fo ema should b write existing
•  DBA also takes backup of the data on a backup storage device so that if data can be lost then it can be again recovered and compiled. 
•  DBA interacts regularly with technical, applications and operational staff to ensure database integrity and security. ernal schem r example,i be possib Creating new user-id, password etc, and also creating the access permissions that each user can or can not enjoy. Controlling and monitoring user access to the database. 
•  DBA is responsible to create user roles, which are collection of the permissions (like read, write etc.) granted and restricted fora class of users. 
•  DBA defines the integrity constraints (like PRIMARY KEY, UNIQUE, NOT NULL etc.) for the database to ensure that the data entered conform to some rules.
•  DBA creates a security mechanism to prevent unauthorized access, accidental or intentional handling of data that can cause security threats.