Dbms

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Dbms

  1. 1. Problems with file processing systems Inconsistent data Inflexibility Limited data sharing Poor enforcement of standards Excessive program maintenance
  2. 2. Levels of Data Character :The most basic logical element is character.Which consists of alphabetic, numeric or other symbol. Field : It consists of grouping of characters.For example, the grouping of alphabetic characters.For example grouping of alphabetic characters in a person’s name form a name field. Record :Related fields of data are grouped to form a record. File :A group of related records is a data file, or table. Database :The highest level in the hierarchy is the database.A database is an integrated collection of logically related records or files.
  3. 3. Objectives of Data Base Controlled Redundancy Ease of learning and use Data independence Accuracy and Integrity Privacy and security Shared Recovery from failure Performance
  4. 4. Types of Data Bases Operational Data Base Analytical Data Base Data Warehouse Data Base Distributed Data Base End User Data Base External Data Base
  5. 5. Operational Database Data Bases store detailed data needed to support operations of entire organization They are also called Subject Area Databases ,transaction database and production database A customer database, inventory database, and other database containing data generated by business operations
  6. 6. Analytical Database Databases store data extracted from selected operational and external databases Consists of data mostly needed by an organization’s managers and other end users They are also called management databases or information databases They are the databases accessed by the online analytical processing (OLAP) systems, decision support systems and executive information systems
  7. 7. Data Warehouse Databases Stores data from current and previous years that has been extracted from various operational and analytical databases of an organization It is a central source of data that has been standardized and integrated so it can be used by managers and other end user professionals throughout an organization
  8. 8. Distributed Database Databases of local work groups and departments at regional offices, branch offices, manufacturing plants and other work sites Can include segments of common operational and common user databases as well as data generated and used only at a user’s own site Ensuring that all the data in distributed databases are consistently and concurrently updated
  9. 9. End User Database These databases consist of a variety of data files developed by end users at their workstations For example, users may have their own electronic copies of documents they generated with word processing packages or received by electronic mail.
  10. 10. External Database Access to external online databases or data banks is available for a fee from commercial information services , or for free of price from many sources on the internet For example, data are available in the form of statistics on economic and demographic activity from statistical data banks Abstracts from newspapers, magazines, and other periodicals from bibliographic data banks
  11. 11. Database Management System DBMS is the software that permits an organization to centralize data, manage them efficiently, and provide access to the stored data by application programs . DBMS acts as an interface between the application program and the physical data files DBMS has three components  A data definition language  A data manipulation language  A data dictionary
  12. 12. Data Definition Language The data definition language is the formal language used by the programmers to specify the content and structure of database It defines each data element as it appears in the database before that data element is translated into the forms required by application programs
  13. 13. Data Manipulation Language This language contains commands that permits end users and programmers to extract data from the database to satisfy information requests and develop applications The most prominent data manipulation language today is structured query language (SQL)
  14. 14. Data Dictionary This is an automated or manual file that stores definitions of data elements and data characteristics such as usage, physical representation, ownership, authorization and security Many data dictionaries can produce lists and reports of data utilization, groupings, program location and so on
  15. 15. Functions of DBMS Organizes data Integrates data Separates data Controls data Retrieves data Protects data
  16. 16. Benefits of DBMS Reduced programming costs Reduced development and implementation time Reduced program and file maintenance costs Reduced data Redundancy Increase flexibility
  17. 17. Data Storage and Retrieval Data is not stored in a random fashion. It is organized for efficient retrieval. Sequential organization Indexed Sequential Organization Inverted List Organization Direct Access Organization
  18. 18. Sequential Organization It simply means storing and sorting in physical, contiguous blocks within files on tape or disk Records are also in sequence within each block It is best suited in reading one record after another without a search delay The records can be added only at the end of the file
  19. 19. Indexed Sequential Organization Data is stored in physically contiguous blocks and uses indexes to locate records Indexed Sequential Organization reduces the magnitude of the sequential search and provides quick access for sequential and direct processing The drawback is the extra storage space required for the index. It also takes long to search the index for data access or retrieval
  20. 20. Inverted List Organization It differ from the previous in the index level and record storage The indexed sequential method has a multiple index for a given key, whereas the inverted list method has a single index for each key type In inverted list records are not needed to be stored in a particular sequence. They are placed in data storage area but indexes are updated for the record keys and location Inverted lists are best for applications that request specific data on multiple keys
  21. 21. Direct Access Organization In direct access file organization, records are placed randomly throughout the file New records are added at the end of the file or inserted in specific locations based on software commands Records are accessed by addresses that specify their disk locations. An address is required for locating a record, for linking records , or for establishing relationships
  22. 22. Hierarchical Data Model Employee Compensation Performance Salary hist Job assignments Pension Benefits Life insurance Health
  23. 23. Network Data Model Course 1 Student 1 Student 2 Course 2 Student 3 Course 3 Student 4 Student 5 Student 6
  24. 24. Relational Data Model Dept .no Dep. A Dep. B Dep. C D D Emp name loc no Emp E E E Dep. . no name title sal no E1 E2 E3 DA DA DB E4 E5 DB DC E6 DA
  25. 25. Data Schemes The schemes (schema) define categories of data and their properties . External Schema or user schema is the user’s view of a part of the database Conceptual Schema is the overall logical view of the database Internal Schema or data storage definition is the way the data is physically organized in storage
  26. 26. General Model External Schemas User View Conceptual Schema User View Internal Schema User View Stored Database
  27. 27. External Schema Each user of the database (an application program or a person formulating a query ) is concerned with only a small portion of the database Each user is interested in only a part of the entities in the database, only part of the attributes of those entities, and certain relationships among the entities External schema consists basically of definitions of each of the various external record types in the external view The external schema is written using the DDL portion of the user’s data sub language
  28. 28. Conceptual Schema The conceptual schema is the logical view of the entire database . It represents as closely as possible the real entities and their relationships . It contains integrity rules and authorization rules, but it does not contain information about how the data items are stored
  29. 29. Internal Schema The internal schema or physical data model describes how the database is organized for physical storage and access The internal schema includes information on ordering of records, block sizes, storage indexes, use of pointers and access strategies being used
  30. 30. Mapping A mapping is a transaction of one schema to another In order for a user to access data, the user view of the data as reflected in the external schema must be translated into the overall conceptual schema In the same way, the conceptual/internal mapping translates logical descriptions of data in the conceptual schema to physical locations and access paths in the internal scheme
  31. 31. Mapping between Schemas view External view External External schema1 External schema 2 Overall conceptual view Conceptual schema Internal schema (DDL) Stored Database External view External schema 3

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