Database system is basically computerized Record Keeping system whose overall purpose is to store information and to allow users to retain update that information on demand. the information can be anything that is of significance to the individual organisation concerned .other way we can find a database is a collection of data that is organised so that its content can easily be accessed managed and updated . database is a collection of related data ,should be integrated and shared . database is a collection of Persistent data that is used by the application system or by given organisation .
Database consists of
- data item
Data item is a distinct piece of information. relationships present across bonding between various data elements. constraints are predicates the define correct database state. schema describes the organisation of data and relationship with in a database. define various views of the database for the use of the use of of the various system component of the database management system and for application security. schema separate the physical aspect of data storage from the logical aspects of data representation.
Now let’s see file oriented approach for data management
flat file consists of only one file or table, which each entry containing all the required data defined within it. it is like a cabinet containing only one folder which has many pages in it, space containing all the information for that specific entry. this means it easy for the user to know where to find requested entries and all the data associated with them. and enter data are at one place, withdrawal of data is easy and fast. but the flat file suffers from the problem of data redundancy. suppose there is an ordering processing application which includes the name, address and phone number of customer. this customer has placed orders for two items then there could be two entries for this customer which is the name ,address and phone number. in other words, the file contains redundant data. that is twice the name, address and phone number of the customer. if he is address to be changed then it is to be changed at two places.
Using this file oriented approach has following disadvantages
- data redundancy and inconsistency
- difficulty in accessing data
- data isolation
- integrity problem
- atomicity problem
Now let’s see what a database management system is
- It is a software package to store and manage database
- DBMS gives the user to access the data and helps them transform the data into information
- The system allows user to create , and extract information from the database,update.
Now let’s see how database can be accessed
Any access to the Stored data is done by the data manager. steps involved in database access can be summarized as in figure
User’s request for data is received by the data manager, which determines the physical record required. the decision as to which physical record is needed me required some preliminary consultation of the database for the data dictionary prior to the axis of the actual data itself.
The data manager science the request for a specific physical record to the file manager. define medicine decide which physical physical block of secondary record and storage devices contain the required record and send the request for appropriate block to the Disk Manager. A block is a unit of physical input output operations between primary and secondary storage. today’s manager you try the block and send it to the file manager, you sent the required record to the data manager.
Components of a DBMS
It transform user’s Query into low level instructions that run on run time database manager
Run Time Data Manager
It handle database access at run time, it accept users Query via Query processor.The run time data manager then place call to the physical database to perform the request.it contains the following component
– it checks whether user has necessary permission to carry out the requiered operation.
-it processes the queries passed by the authorization control module
-it checks for necessary integrity constraints for all the requested operations that change the database
-it ensures that transaction request and release locks according to a suitable locking protocol it schedules execution of transaction
– it is responsible for ensuring that concurrent operation on the database proceed without conflicting with one another
-it has two components
- recovery manager ensure that the database remain in a consistent state in the presence of tailor it is responsible for transaction commit and abort operation it maintains a long and storing the system to a consistent state after crash
- buffer manager: is responsible for the transfer of data between the main memory and secondary storage
-the DML compiler converts the DML statement into object code for database access
-it converts real statements into a set of tables containing metadata. vegetables contain the metadata concerning the database vendor in a form that can be used by other components of a database.
Typically, DBMS has three components, provides the following facilities.
- data definition language DDL: it allows used to define the database, specify the data types, and data structures, and the constraints on the data to be stored in the database, usually through data definition language. DDL translate the schema written written in a source language into the object schema, thereby creating a logical and physical layout of the database.
- data manipulation language (DML) Query facility: it allows user to insert,, update, delete and retrieve data from database, usually through the data manipulation language. it provides general query facility through structured query language SQL.
- software for controlled access of database: it provides control access to the database, for example, preventing unauthorised user trying to access the database, providing a con currency control system to allow shared access of the database, activating a recovery control system to restore the database 2A previous consistent state following your hardware or software failure.
Now let’s see operation performed on database system
- Adding new, empty file to the database.
- Inserting data into existing files changing, deleting removing the existing file from the database.
Advantage of DBMS:
- reduction of redundancies that is duplication .
- shared data:
- Data integrity: Data integrity means get the data contained in database is both accurate and consistent.
- data security: data is of vital important to an organisation it may be confidential. such a confidential data must not be accessed by unauthorized persons.
- conflict resolution is the database under control of DBA. you should resolve the conflicting requirements various users and applications.
- data independence: is usually considered from two point of you
physical data independence: it allows changes in the physical storage devices or organisation of the files to be made without requiring change in the conceptual view or any of the external views and hence in the application programs use the database. so the file may migrate from one type of physical media to another or the file structure may change without any need for change in the application programs.
logical data independence: it implies that application programs did not to be changed if the fields are added to an existing record. it indicates that the conceptual schema can be changed without affecting the existing external schemas
Now let’s see disadvantages of DBMS
- the cost of using DBMS is higher.
- the problem associated with centralization.
- cost of Software and Hardware and migration
- complexity of backup and recovery.
Data administrator DA: data administrator is an identified individual person in the organisation who has the central responsibility of controlling data
Database administrator DBA:
DBA is responsible for the overall control of the system at technical level. like who can perform operation on what data in in what circumstances.
Following are the responsibilities of the DBA
- defining the conceptual schema: to identify the entities of interest to the Enterprise, and to identify the information to be recorded about those entities. this process is referred to as a logical/ conceptual database design.
- defining the internal schema: the DBA but also decide how the data is to be represented in the Stored database. this process is usually referred as physical database design. you also defines the associated internal mapping.
- defining security and integrity constraint
- storage structure and access method definition
- granting of authorization for data access
- defining dump and reload policies