Database Management Systems


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Database management system is a computer software system that has been designed to manage databases, Oracle, DB2, Microsoft Access among others are examples of DBMS.

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Database Management Systems

  1. 1. I.T. for Management Chapter 8 Database Management Systems
  2. 2. Database Management SystemsA database management system (DBMS) iscomputer software designed for the purpose ofmanaging databases.Typical examples of DBMSs include Oracle, DB2,Microsoft Access, Microsoft SQL Server, MySQL,4th Dimension and FileMaker. DBMSs aretypically used by Database administrators in thecreation of Database systems.
  3. 3. Database Management SystemsA DBMS is a complex set of software programs thatcontrols the organization, storage and retrieval of datain a database. A DBMS includes: 1.A modeling language to define the schema(relational model) of each database hosted in the DBMS, according to the DBMS data model.The three most common organizations are the hierarchical,network and relational models. A database managementsystem may provide one, two or all three methods. Invertedlists and other methods are also used. The most suitablestructure depends on the application and on the transactionrate and the number of inquiries that will be made.
  4. 4. Database Management SystemsThe dominant model in use today is the ad hoc oneembedded in SQL, a corruption of the relational model byviolating several of its fundamental principles. Many DBMSsalso support the Open Database Connectivity API thatsupports a standard way for programmers to access theDBMS.Data structures (fields, records and files) optimized to dealwith very large amounts of data stored on a permanent datastorage device (which implies very slow access compared tovolatile main memory).
  5. 5. Database Management Systems 1.A database query language and report writer to allow users to interactively interrogate the database, analyse its data and update it according to the users privileges on data. It also controls the security of the database.Data security prevents unauthorised users from viewing orupdating the database. Using passwords, users are allowedaccess to the entire database or subsets of it calledsubschemas. For example, an employee database can containall the data about an individual employee, but one group ofusers may be authorized to view only payroll data, whileothers are allowed access to only work history and medicaldata
  6. 6. Database Management Systems 1.A transaction mechanism, that ideally would guarantee the ACID properties, in order to ensure data integrity, despite concurrent user accesses (concurrency control), and faults (fault tolerance). oIt also maintains the integrity of the data in the database.The DBMS can maintain the integrity of the database by notallowing more than one user to update the same record at thesame time. The DBMS can help prevent duplicate records viaunique index constraints; for example, no two customerswith the same customer numbers (key fields) can be enteredinto the database. See ACID properties for more information(Redundancy avoidance).
  7. 7. Database Management SystemsRelational DBMSEdgar Codd worked at IBM in San Jose, California, inone of their offshoot offices that was primarilyinvolved in the development of hard disk systems. Hewas unhappy with the navigational model of theCodasyl approach, notably the lack of a "search"facility which was becoming increasingly useful whenthe database was stored on disk instead of tape. In1970, he wrote a number of papers that outlined a newapproach to database construction that eventuallyculminated in the groundbreaking A Relational Modelof Data for Large Shared Data Banks.[1]
  8. 8. Database Management SystemsIn this paper, he described a new system for storingand working with large databases. Instead ofrecords being stored in some sort of linked list offree-form records as in Codasyl, Codds idea was touse a "table" of fixed-length records. A linked-listsystem would be very inefficient when storing"sparse" databasesWhere some of the data for any one record could be leftempty. The relational model solved this by splitting the datainto a series of normalized tables, with optional elementsbeing moved out of the main table to where they would takeup room only if needed
  9. 9. Database Management SystemsIn the relational model, related records are linkedtogether with a "key".
  10. 10. Database Management SystemsFor instance, a common use of a database system is to trackinformation about users, their name, login information,various addresses and phone numbers. In the navigationalapproach all of these data would be placed in a single record,and unused items would simply not be placed in thedatabase. In the relational approach, the data would benormalized into a user table, an address table and a phonenumber table (for instance). Records would be created inthese optional tables only if the address or phone numberswere actually provided
  11. 11. Database Management Systems FeaturesShared database with concurrency Control:This means that the DBMS allows many usersto access the data at the same time which isvery essential for on line systemsApplication of business rules:In a situation where many people aresimultaneously updating database ,it is essentialthat all users go through same checks &controls .for example user may access toparticular table for viewing & not updating
  12. 12. Database Management Systems FeaturesRole based access :The DBMS allow the database administrator tocreate user roles whereby he can define to whateach user can do to the database.Views: DBMS allows creation of ‘views’ A view is aquery written in SQL which provides a subset of thedatabaseTransaction control:One of the main purpose of a DBMS is to helpimplement business transaction ……. Cont
  13. 13. Database Management Systems FeaturesData independence:With changing business needs it is important thatwe are are able to add more columns or change theproperties of a columnPlatform independence:Many DBMS are available for a wide variety ofoperating systems& hardware.Thus data can bemigrated from on environment to another sinceDBMS allow import & export of database. Cont……..
  14. 14. Database Management Systems FeaturesSupport for various language interface:Though DBMS use SQL business data processingrequires more complex manipulation & presentationof reports& user friendly screen Updating thedatabase are embedded in commonly usedlanguages such as Cobol, java etc.Referential integrality:The DBMS ensures that if record is deleted allcorresponding child records are deleted
  15. 15. Database Management Systems FeaturesGrowth :DBMS are highly sensitive systems DBMSsoftware such as oracle,Sybase,SQL server etc canhandle very high volumes of data &transactions.Thus database can span across severaldisks,distributed over several database serversDistributed Database:DBMS allow users to execute transactions whichaccess & update information from any location
  16. 16. File & various types of DatabaseOriginally all data on computers was in the formof flat files.These file were :Serial files:each record was stored after the otherin a serial orderSequential files:each record was stored afteranother based on some sequence such as customercode which made it easier to accessRandom files:data could be accessed randomlyIndex files: Here two file are kept one filecontains data which is any order other filecontains index
  17. 17. Disadvantages of desecrate filesThe programmer who develops an application needto know a lot about files,where it is storedHow it is accessed What Is Structure.Each programmer writes differentstructure,different formats.Thus there is duplication of same dataIn case data is required in sequential order fileshave been sorted & usedThe flat file system do not offer anysecurity,Integrity and transaction control
  18. 18. How does the DBMS Store information A DBMS maintains the following information Business Data Meta Data More information about data Business &integrity rules User related information Who are the authorized user Which tables & columns can they acce Are they restricted to specific time of d ………..cont
  19. 19. How does the DBMS Store informationWhen we create a database we have to take holisticview of all users of the database & there needsA database consists of schema or layout consistingof various pieces of information grouped together inthe form of entities.Apart from master tables we need to definetransaction tables.Transaction tables are thosewhere transaction information is storedOnce the database is created the transaction hasbeen created thru application software
  20. 20. Database languagesThere are three types of database languages usedData Definition languages:A language to define & alter the structure of thedatabaseData manipulation language:A language or set of commands to query,add ,ordelete records in database.Data control language:A language which helps to define user rulestoaccess data
  21. 21. SQL Data Manipulation commands SQL Data Manipulation commands Data manipulation requires four basic functions Select Insert Update Delete SQL performs these tasks very efficiently.
  22. 22. Database languages Typical SQL Commands create table phone_numbers ( email varchar(100) not null references mailing_list, number_type varchar(15) check (number_type in (work,home,cell,beeper)), phone_number varchar(20) SQL> insert into phone_numbers values (,work,(800) 555- 1212);
  23. 23. Types of Database DBMS are of atleast 4 types Hierarchical DBMS Network DBMS Relational DBMS Object DBMS
  24. 24. Types of DatabaseHierarchical DBMSStore information in the form of a Hierarchy ofrecords ie parent child formationThus a hierarchical structure is created with thelinks pointing from parent records to child records.Network DBMSNetwork DMBS overcome some of inflexibilitiesof Hierarchical DBMS the data administrator byallowing pointers ……Cont
  25. 25. Types of Database Relational Database (RDBMs) The concept of RDBMS revolutionaries the DBMS & widely accepted all overA relational database is a big spreadsheet that:several people can update simultaneously.A request might be "create a table", "insert a rowinto a table", "update an existing row in a table","give me a report of the information contained in allthe rows in a table that meet the followingcriteria...". ……….Cont
  26. 26. Types of DatabaseRelational Database (RDBMs)Each table in the database is one spreadsheet. Youtell the RDBMS how many columns each row has.For example, in our mailing list database, the tablehas two columns: name and e-mail. Each entry inthe database consists of one row in this table. AnRDBMS is more restrictive than a spreadsheet inthat all the data in one column must be of the sametype, e.g., integer, decimal, character string, or date.Another difference between a spreadsheet and anRDBMS is that the rows in an RDBMS are notordered.
  27. 27. Types of DatabaseRelational Database (RDBMs)Entities & TuplesEach table represents information which is relatedto the entity such as employeeAll data related to an entity (employee) is storedin one row also known as Tuples in RDBMSThe unique identifier for an entity (employee code )Is known as primary keyThe primary key uniquely identifies a row in adatabase
  28. 28. Types of DatabaseAdvantages of Relational Database (RDBMs) Conceptually simple mathematically rigorousVery flexible since We can query on any columnThe database can grow very easily since any numberof records can be added to a table.The database is very expandable since we can add columns to existing tableAs a result databases like Oracle,Sybase,SQL server have become very popular
  29. 29. Types of DatabaseObject DBMSThe success of DBMS system depends upon its ability to represent the data which is very closeTo that in real lifeFor instance if there is a column containinginformation about temperature in degreescentigrade ,it will be helpful if it is converted inFahrenheit along with the column in the metadataDBMS allow such features are known as objectDBMS
  30. 30. Database Management Systems End of Chapter 8