DATABASE MANAGEMENT SYSTEM ARCHITECTURE

Transcription

1 DATABASE 1 MANAGEMENT SYSTEM ARCHITECTURE

2 DBMS ARCHITECTURE 2 The logical DBMS architecture The physical DBMS architecture

3 DBMS ARCHITECTURE 3 The logical DBMS architecture The logical architecture deals with the way data is stored and presented to users. The physical DBMS architecture

4 DBMS ARCHITECTURE 4 The logical DBMS architecture The physical architecture is concerned with the s/w components that make up a DBMS. The physical DBMS architecture

5 Three Level Architecture of DBMS 5 A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data is stored and maintained. External or View Level Conceptual Level Internal or Physical Level

6 Three Level Architecture of DBMS 6 continue External Level View 1 View 2 View 3 Conceptual Level Physical Level

7 Three Level Architecture of DBMS Sales Officer Inventory Controller 7 continue External Level View 1 Item_Name Price View 2 Item_Name Stock Conceptual Level Conceptual Item_Number Character (6) Item_Name Character(30) Price Numeric(5,2) Stock Numeric(4) Physical Level Physical Stored_Item Length=50 Item # Type = Byte(6), offset = 0, Index = Ix Name Type = Byte(30), offset = 6 Price Type = Byte(8), offset = 36 Stock Type = Byte(4), offset = 44

8 External or View Level 8 This level is closest to the users and is concerned with the way in which the data is viewed by individual users. Most of the users are not concerned with all the information contained in the database. Instead they need only a part of the database relevant to them. The system provides many views for the same database.

9 External or View Level 9 continue Highest level of abstraction of database. Allows to see only the data of interest to them. Users Application programmers or end-users. Any no. of external views external schema.

10 External or View Level 10 continue It consists of the definition of logical records and relationships in the external view. It also contains the methods for deriving the objects such as entities, attributes and relationships in the external view from the Conceptual View.

11 Conceptual Level 11 This level of abstraction describes what data are actually stored in the database. It also describes the relationships existing among data. At this level, the database is described logically in terms of simple data-structures. The users of this level are not concerned with how these logical data structures will be implemented at the physical level, rather they just are concerned about what information is to be kept in the database.

12 Conceptual Level 12 continue The sum total of DBMS users view. Describes what data are actually stored in the database (ie,all the records and relationships included in the database).

13 Conceptual Level 13 continue The conceptual view is a representation of the entire information content of the database in a form that is some what abstract in comparison with the way in which the data is physically stored.

14 Conceptual Level 14 continue The conceptual view is defined by means of the conceptual schema, which includes the definition of each of the various types of conceptual records and the mapping between the conceptual schema and the internal schema.

15 Internal or Physical Level 15 Lowest level of abstraction. Describes how the data are physically stored. Internal view internal schema (not only defines the various types of stored record but also specifies what indexes exists, how files are represented, etc.)

16 Internal or Physical Level 16 The internal level is closest to physical storage. This level is also termed as physical level. It describes how the data are actually stored on the storage medium. At this level, complex low-level data structures are described in detail.

17 Data Independence 17 TDATA INDEPENDENCE Physical Data Independence Logical Data Independence

18 Physical Data Independence 18 It refers to the ability to modify the scheme followed at the physical level without affecting the scheme followed at the conceptual level. The application programs remain the same even though the scheme at the physical level gets modified. Modifications at the physical level are occasionally necessary in order to improve performance of the system.

19 Logical Data Independence 19 It refers to the ability to modify the conceptual scheme without causing any changes in the schemes followed at view levels. The logical data independence ensures that the application programs remain the same. Modifications at the conceptual level are necessary whenever logical structures of the database get altered because of some unavoidable reasons.

20 Physical & Logical Data Independence 20 It is more difficult to achieve logical data independence than the physical data independence. The reason being that the application programs are heavily dependent on the logical structure of the database.

21 Physical DBMS Architecture 21 Describes the software components used to enter and process data. How these s/w components are related and interconnected.

22 DBMS Structure General users AP Query DBA 22 Application Programs System Calls Schema Object Code Of Program DML Precompiler Query Processor DDL Compiler File Data Files Data Dict.

23 DBMS Structure General users AP Query DBA 23 Application Programs System Calls Schema Object Code Of Program DML Precompiler Query Processor DDL Compiler DDL set of commands required to define the format of data. DML set of commands that modify, process data. DML precompiler converts DML statements File embedded in an application program to normal procedural calls in the host language. It interacts with the query processor in order to generate the appropriate code. Data Files Data Dict.

24 DBMS Structure General users AP Query DBA 24 Application Programs System Calls Schema Object Code Of Program DML Precompiler Query Processor DDL Compiler DDL compiler converts DDL statements into a set of tables containing metadata tables which are File in a form that can be used by other components of the DBMS. These are stored in system catalog or data dictionary. Data Files Data Dict.

25 DBMS Structure General users AP Query DBA 25 Application Programs System Calls Schema Manages the allocation of space on disk storage. Object Code Of Program DML Precompiler Query Processor DDL Compiler File Data Files Data Dict.

26 DBMS Structure General users AP Query DBA 26 Application Programs System Calls Schema Object Code Of Program DML Precompiler Query Processor DDL Compiler File Responsible for receiving query language statements and changing to a form the DBMS can understand. It has two parts : (i) parser (ii) query optimizer Data Files Data Dict.

27 DBMS Structure General users AP Query DBA 27 Application Programs Object Code Of Program System Calls It is the interface b/w lowlevel data, application programs and queries. It enforces constraints to DML Precompiler maintain the consistency and integrity of the data as well as its security. It synchronizes the concurrent access. It also perform backup and recovery operations. Query Processor File Schema DDL Compiler Data Files Data Dict.

28 DBMS Structure General users AP Query DBA 28 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery Buffer DML Precompiler Query Processor File Schema DDL Compiler Data Files Data Dict.

29 DBMS Structure General users AP Query DBA 29 Components Application Programs System Calls Schema Authorization Control Command Processor Object Code DML Query DDL Integrity Of Program CheckerPrecompiler Processor Compiler Query Optimizer Transaction Scheduler Recovery Buffer File Checks that the user has necessary authorization to carry out the required function. Data Files Data Dict.

30 DBMS Structure General users AP Query DBA 30 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery Buffer DML Precompiler Query Processor File Schema DDL Compiler Converts commands to a logical sequence of steps. Data Files Data Dict.

31 DBMS Structure General users AP Query DBA 31 Components Application Programs System Calls Schema Authorization Control Command Processor Object Code DML Query DDL Integrity Of Program CheckerPrecompiler Processor Compiler Query Optimizer Transaction Scheduler Recovery Buffer File Checks the requested operation satisfies all necessary integrity constraints such as key constraints. Data Files Data Dict.

32 DBMS Structure General users AP Query DBA 32 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery DML Precompiler Query Processor Data Files Schema DDL Compiler Examines the query language statements and tries to Buffer File choose the best and most efficient way to executing the query. Factors CPU time, disk time, network time, sorting methods and scanning methods. Data Dict.

33 DBMS Structure General users AP Query DBA 33 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery Buffer DML Precompiler Query Processor File Schema DDL Compiler The transaction manager maintains tables of authorization concurrency. Data Files Data Dict.

34 DBMS Structure General users AP Query DBA 34 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery Buffer DML Precompiler It controls the relative order operations are executed. Query Processor File Schema DDL Compiler in which transaction Data Files Data Dict.

35 DBMS Structure General users AP Query DBA 35 Components Application Programs System Calls Authorization Control Command Processor Object Code Integrity Of Program Checker Query Optimizer Transaction Scheduler Recovery Buffer DML Precompiler Query Processor File Data Files Schema DDL Compiler Ensures that the database remains in a consistent state in the presence of failures. Responsible for transaction commit and abort. Data Dict.

36 DBMS Structure General users AP Query DBA 36 Components Application Programs System Calls File Schema Authorization Control Command Processor Object Code DML Query DDL Integrity Of Program CheckerPrecompiler Processor Compiler Query Optimizer Responsible for the transfer of data between main Transaction memory and secondary storage. Scheduler Recovery Buffer Data Files Data Dict.

37 System Utilities Apart from software modules most DBMS have database utilities that help the DBA manage the database system. Common utilities have the following types of functions. Loading Backup storage reorganization Performance monitoring 37

38 System Utilities 38 Loading A loading utility is used to load existing data files into the database. Usually, the current format of the data file and the desired database file structure are specified to the utility, which then automatically reformats the data and stores in the database.

39 System Utilities 39 Backup A backup utility creates a backup copy of the database. The backup copy can be used to restore the database in case of catastrophic failure.increental backups are also often used, where only changes since the previous backup are recorded.

40 System Utilities storage reorganization This utility can be used to reorganize a set of database files into different file organization to improve performance.. Performance Monitoring - Such a utility monitors database usage and provides statistics to the DBA. The DBA uses the statistics in making decisions such as whether or not to reorganize files or whether to add or drop indexes to improve performance 40