Execution Steps of DBMS – Sequence of events When DBMS Reads A Record –
Execution Steps of DBMS –
The events that occur when an application program reads a record by means of DBMS is shown in fig.
- Application Program A issues a request to the DBMS to read a record.
- The DBMS obtains the subschema and look up the description of the data in question.
- The DBMS obtains the schema and determines which logical data types are needed.
- The DBMS contains the physical data base description and determines which physical record(s) to be read.
- A command is issued by the DBMS to the operating system to read the required record(s).
- The operating system interacts which the physical storage where the data are kept.
- The required data are transferred between the storage an the system buffers.
- Comparing the schema and the subschema, the DBMS derives from the data, the logical record needed by the application program.
- The data is transferred by the DBMS from the system buffers to the program work area.
- The status information is given by the DBMS to the application program, included any error indication.
- The application program then operates with the data in a work area.
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