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Explain DBMS.
Post: #1

A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, and the use of a database. It allows organizations to place control of database development in the hands of database administrators (DBAs) and other specialists. A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different user application programs to easily access the same database. DBMSs may use any of a variety of database models, such as the network model or relational model. In large systems, a DBMS allows users and other software to store and retrieve data in a structured way. Instead of having to write computer programs to extract information, user can ask simple questions in a query language. Thus, many DBMS packages provide Fourth-generation programming language (4GLs) and other application development features. It helps to specify the logical organization for a database and access and use the information within a database. It provides facilities for controlling data access, enforcing data integrity, managing concurrency, and restoring the database from backups. A DBMS also provides the ability to logically present database information to users.
• DBMS Engine accepts logical requests from various other DBMS subsystems, converts them into physical equivalents, and actually accesses the database and data dictionary as they exist on a storage device.
• Data Definition Subsystem helps the user create and maintain the data dictionary and define the structure of the files in a database.
• Data Manipulation Subsystem helps the user to add, change, and delete information in a database and query it for valuable information. Software tools within the data manipulation subsystem are most often the primary interface between user and the information contained in a database. It allows the user to specify its logical information requirements.
• Application Generation Subsystem contains facilities to help users develop transaction-intensive applications. It usually requires that the user perform a detailed series of tasks to process a transaction. It facilitates easy-to-use data entry screens, programming languages, and interfaces.
• Data Administration Subsystem helps users manage the overall database environment by providing facilities for backup and recovery, security management, query optimization, concurrency control, and change management.
Post: #2
Basics of DBMS

.docx  Basics of DBMS.docx (Size: 188.98 KB / Downloads: 195)


Database Management System (DBMS) is a collection of interrelated data [usually called database] and a set of programs to access, update and manage those data [which form part of management system].

Primary goals of DBMS are:

1. To provide a way to store and retrieve database information that is both convenient and efficient.
2. To manage large and small bodies of information. It involves defining structures for storage of information and providing mechanism for manipulation of information.
3. It should ensure safety of information stored, despite system crashes or attempts at unauthorized access.
4. If data are to be shared among several users, then system should avoid possible anomalous results.

Applications of DBMS:

1. Banking – For customer information, accounts, and loans, and banking transactions. [all transactions]
2. Airlines – For reservation and schedule information. [reservations, schedules]
3. Universities – For student information, course registrations, and grades. [registration, grades]
4. Credit Card Transactions – For purchases on credit card and generation of monthly statements.
5. Telecommunication – For keeping records of calls made, generating monthly bills, maintaining balances on prepaid calling cards, and storing information about communication networks.
6. Finance – For storing information about holdings, sales, and purchases of financial instruments such as stocks and bonds.
7. Sales – For customer, product, and purchase information. [customers, products, purchases]
8. Manufacturing – For management of supply chain and for tracking production of items in factories, inventories of items in warehouses/stores, and orders for items. [production, inventory, orders, supply chain]
9. Human Resources – For information about employees, salaries, payroll taxes and benefits, and generation of paychecks. [employee records, salaries, tax deductions]

Data and Information:

Data are raw facts or observations typically about physical phenomenon or business transactions. More specifically data are objective measurements of the attributes (or characteristics) of entities (such as people, places, things and events)

Data Organization and Grouping:

Data as we already mentioned occurs in real world individually. But it is grouped and organized to help process it and generate information.
The grouping of related data items from user’s view is called logical grouping. The grouping of data items from the point of view of its storage inside the computer is called physical grouping.
Just as writing is organized in letters, words, sentences, paragraphs and chapters, Data can be organized as characters, fields, records, files and databases.
Post: #3
to get information about the topic "DBMS" full report ppt and related topic refer the link bellow
Post: #4

.ppt  DATABASE MANAGEMENT.ppt (Size: 323.5 KB / Downloads: 97)

Recovery and Atomicity

Modifying the database without ensuring that the transaction will commit may leave the database in an inconsistent state.
Consider transaction Ti that transfers $50 from account A to account B; goal is either to perform all database modifications made by Ti or none at all.
Several output operations may be required for Ti (to output A and B). A failure may occur after one of these modifications have been made but before all of them are made.

Recovery Algorithms

Recovery algorithms are techniques to ensure database consistency and transaction atomicity and durability despite failures
Focus of this chapter
Recovery algorithms have two parts
Actions taken during normal transaction processing to ensure enough information exists to recover from failures
Actions taken after a failure to recover the database contents to a state that ensures atomicity, consistency and durability

Log-Based Recovery

A log is kept on stable storage.
The log is a sequence of log records, and maintains a record of update activities on the database.
When transaction Ti starts, it registers itself by writing a <Ti start>log record
Before Ti executes write(X), a log record <Ti, X, V1, V2> is written, where V1 is the value of X before the write, and V2 is the value to be written to X.
Log record notes that Ti has performed a write on data item Xj Xj had value V1 before the write, and will have value V2 after the write.
When Ti finishes it last statement, the log record <Ti commit> is written.
We assume for now that log records are written directly to stable storage (that is, they are not buffered)
Two approaches using logs
Deferred database modification
Immediate database modification

Deferred Database Modification

The deferred database modification scheme records all modifications to the log, but defers all the writes to after partial commit.
Assume that transactions execute serially
Transaction starts by writing <Ti start> record to log.
A write(X) operation results in a log record <Ti, X, V> being written, where V is the new value for X
Note: old value is not needed for this scheme
The write is not performed on X at this time, but is deferred.
When Ti partially commits, <Ti commit> is written to the log
Finally, the log records are read and used to actually execute the previously deferred writes.


Problems in recovery procedure as discussed earlier :
searching the entire log is time-consuming
we might unnecessarily redo transactions which have already
output their updates to the database.
Streamline recovery procedure by periodically performing checkpointing
Output all log records currently residing in main memory onto stable storage.
Output all modified buffer blocks to the disk.
Write a log record < checkpoint> onto stable storage.

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