Explain overall structure of DBMS. (10 Marks, Mumbai University)

Database Management System

Explain overall structure of DBMS. 

Answer: 

Fig. Structure of DBMS

(Source: Database System concepts, Abraham Silberschatz, Henry F.Korth, S.Sudarshan)

1. Database Users:

• Naive User: Naive users are users who interact with the database through an application interface or third party software (like tally) Ex: Office clerks

• Application programmer: Developer who’s had knowledge about database (e.g. knowledge about DML queries),with the help of that they used database features to integrate within there application(e.g. Web-application, mobile app) to provide storage capability for their application. Also they have explicit write permission for databases.  Ex: Software Engineers.

• Sophisticated users: They played the role of analysts in Database management. They overlook the overall structure of the database. They access the database with a special query tool. Ex: System Analyst.

• Database administrator: DBA is a super user of database who deals with administration and permissions or authorization. They have explicit permission to grant the authorization for database, read/write in particular data sets and all related to data management. They usually access the database with an administration tool which is exclusive for data administrators. Ex: DBA

2. Query Processor : 

It interprets the requests (queries) received from end user via an application program into instructions.

It also executes the user request which is received from the DML compiler. 

The components of Query Processor contains the following: 

 

• DML Compiler –
  It processes the DML statements into low level instruction (machine language), so that they can be executed.

• DDL Interpreter –
  It processes the DDL statements into a set of table containing meta data (data about data).
  

• Query evaluation engine–
  It executes the instruction generated by DML Compiler.

• Storage Manager: A storage manager is a program module that provides the interface between the low level data stored in the database and the application programs and queries submitted to the system. The storage manager is responsible for the interaction with the file manager. The raw data are stored on the disk using the file system, which is usually provided by a conventional operating system. The storage manager translates the various DML statements into low-level file-system commands. Thus, the storage manager is responsible for storing, retrieving, and updating data in the database.

The storage manager components include:

1. Authorization and integrity manager, which tests for the satisfaction of integrity constraints and checks the authority of users to access data.

2. Transaction manager, which ensures that the database remains in a consistent (correct) state despite system failures, and that concurrent transaction executions proceed without conflict.

3. File manager, which manages the allocation of space on disk storage and the data structures used to represent information stored on disk.

4. Buffer manager, which is responsible for fetching data from disk storage into main memory, and deciding what data to cache in main memory. The buffer manager is a critical part of the database system, since it enables the database to handle data sizes that are much larger than the size of main memory.

5. Transaction Manager, A transaction is a collection of operations that performs a single logical function in a database application. Each transaction is a unit of both atomicity and consistency. Thus, we require that transactions do not violate any database-consistency constraints. That is, if the database was consistent when a transaction started, the database must be consistent when the transaction successfully terminates. Transaction - manager ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.

 

• . Disk Storage : 

  It contains the following components – 

1. Data Files:
   It stores the data. 

2. Data Dictionary:
   It contains the information about the structure of any database object. It is the repository of information that governs the metadata. 

3. Indices:
   It provides faster retrieval of data item.

 Useful Video Links:

1) Drawbacks of File Processing System (FPS) 

 2) Levels of abstraction in DBMS

 3) Physical Data Independence and Logical Data Independence in DBMS