Database management systems address the need to store, retrieve, and manipulate large amounts of data in an organized fashion. The use of databases to store and manage data has grown tremendously in the last 25 years. The database industry is growing steadily as more organizations begin to employ some form of data management. Industrial and academic research has been instrumental in this growth. Theory has played an important role in defining the right abstractions and concepts, and providing a firm foundation for the field. In order to access effectively a large volume of data, one needs an abstract logical view of the data, which must be separate from the physical storage of data. The important first component of a database is therefore an abstract view of data (called the data model) and the accompanying specialized high-level language that is used to access the data. The second important component is the data structures that are used to store the data along with the algorithms to support the efficient translation from the logical to the physical world. The third component is the mechanisms that allow the database to be accessed concurrently by many users, without violating its integrity.
· Update: read, insert and change records
· Lost updates: This event occurs when two transactions read the same data, attempt to update that data, and one of the updates is lost.
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