Shree Secondary School

Lock Based Concurrency Control Protocols – A lock is a variable associated with a data item that describes a status of data item with respect to possible operation that can be applied to it. They synchronize the access by concurrent transactions to the database items. It is required in this protocol that all the data items must be accessed in a mutually exclusive manner. Let me introduce you to two common locks which are used and some terminology followed in this protocol. 1.     Shared Lock (S):  also known as Read-only lock. As the name suggests it can be shared between transactions because while holding this lock the transaction does not have the permission to update data on the data item. S-lock is requested using lock-S instruction. 2.     Exclusive Lock (X):  Data item can be both read as well as written. This is Exclusive and cannot be held simultaneously on the same data item. X-lock is requested using lock-X instruction. Lock Co...

1.     Define Database Management System. A database-management system (DBMS) is a computer-software application that interacts with end-users, other applications, and the database itself to capture and analyze data. A general-purpose DBMS allows the definition, creation, querying, update, and administration of databases. OR A database management system (DBMS) is a collection of programs that enables you to store, modify, and extract information from a database. OR A database management system (DBMS) is a software package designed to define, manipulate, retrieve and manage data in a database. A DBMS generally manipulates the data itself, the data format, field names, record structure and file structure. OR A database management system (DBMS) is the software that allows a computer to store, retrieve, add, delete, and modify data. A DBMS manages all primary aspects of a database, including mana...