Components of DBMS –
A DBMS software is partitioned into several modules or components and each module or component is assigned a specific operation to perform. While designing a DBMS, its interface must be taken into account with the OS as some of the functions of DBMS are supported by OS to provide basic services and DBMS is built on top of it. The functional components of a database system can be broadly divided into –
- Query Processor Component: It simplify and facilitate access to data (convenient and efficient)
- Storage Manager Component: It minimize the need to move data between disk and main memory
- Transaction Manager Component: It handle atomicity and concurrency of transactions and consistency and durability of the databases
Query Processor Component –
Query Processor- Query processor is used to interpret the online user query and converts it into an efficient series of operation in a form capable of being send to the data manager for execution. The query processor use the data dictionary to find the structure of the relevant portion of the data base and use this information in modifying the query and prepare an optimal plan to access the database. It is a program module that provides the interface between the database and the application programs/queries. The Query Processor Components include –
- Data Definition Language(DDL) Compler- DDL compiler takes the data definition statement that is the source form & convert them into the object form (or) interprets DDL commands and records them in the
- Data Modelling Language (DML) compiler – translates DML commands into query evaluation
- Query evaluation engine – executes queries according to the plans
Storage Manager Component –
A Storage Manager is a component or program module that provides the interface between the low-level data stored in the database
and the application programs/queries submitted to the system. The Storage Manager Components include –
- File Manager- File manager manages the file space and it takes care of the structure of the file. It manages the allocation space on disk storage and the data structures used to represent info stored on other media.
- Buffer Manager – It transfers blocks between disk (or other devices) and Main Memory. A DMA (Direct Memory Access) is a form of Input/Output that controls the exchange of blocks process. When a processor receives a request for a transfer of a block, it sends it to the DMA Controller which transfers the block uninterrupted.
- Authorization and Integrity Manager – This Component of storage manager checks for the authority of the users to access and modify information, as well as integrity constraints (keys, etc).
- Disk Manager- The block requested by the file manager is transferred by the Disk Manager.
The Structures maintained by Storage manager are-
- Data Files- Data files contains the data portion of the data base.
- Data Dictionary- DBMS must a data dictionary function. The dictionary contains the data about the data. Rather than just raw data. The information about attributes, entity, mapping & cross reference information is contained in the data dictionary.
- Indices or Indexing and Access Aids – An index is a small table having two columns in which the first column contains a copy of the primary or candidate key of a table and the second column contains a set of pointers holding the address of the disk block where that particular key value can be found. The advantage of using indices is that index makes search operation perform very fast.
In a data base system, a set of access aids in the form of indexes are usually provided to improve the performance of a database system.
Transaction Manager Component/Data Manager –
A Transaction is a collection of operations that performs as a single logical function in a database application. All Transactions must follow transction properties, which are called ACID Properties. Data Manager converts the user queries from the user logical view to a physical file system.
The ACID Properties are –
- Atomicity: either all operations succeed or all of them fail
- Consistency: the database is changed from one consistent state to another consistent state
- Isolation: no transaction interfere other transactions in the middle
- Durability: operations of successful transactions must persist
The Components included by Transaction Manager is –
- Transaction Manager – Transaction Manager controls the execution of transactions.
- Lock Manager – Access of items in DBMS is controlled by LOCKS. And the part of DBMS that keeps a record of locks issued to transactions, is done by the Lock Manager. It maintains a LOCK table which is a hash table, with data object identifier as the key
- Recovery Manager – Recovery manager is responsible for atomicity and durability. It allows DBMS to restore the database to a consistent state following a failure.
Tele-Communication System- Online user of the computer system whether remote or local communicate with it by sending and receving message over communication line. These messages are routed by communication line.
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