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Database Systems Concepts with Oracle CD (Hardcover)
by [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] (Author), [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] (Author), [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] (Author)


Book Description
The Fourth edition of Database System Concepts has been extensively revised from the 3rd edition. The new edition provides improved coverage of concepts, extensive coverage of new tools and techniques, and updated coverage of database system internals. This text is intended for a first course in databases at the junior or senior undergraduate, or first-year graduate level. Database System Concepts, 4th ed. offers a complete background in the basics of database design, languages, and system implementations. Concepts are presented using intuitive descriptions, and important theoretical results are covered, but formal proofs are omitted. The fundamental concepts and algorithms covered in Database System Concepts 4th ed. are based on those used in existing commercial or experimental database systems. The authors present these concepts and algorithms in a general setting that is not tied to one particular database system.



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Purpose of Database Systems

1. To see why database management systems are necessary, let's look at a typical ``file-processing system'' supported by a conventional operating system.
   The application is a savings bank:
   
   
   
   • Savings account and customer records are kept in permanent system files.
     
   • Application programs are written to manipulate files to perform the following tasks:
     
     
     
     • Debit or credit an account.
       
     • Add a new account.
       
     • Find an account balance.
       
     • Generate monthly statements.
       

</LI>

Development of the system proceeds as follows:

• New application programs must be written as the need arises.
  
• New permanent files are created as required.
  
• but over a long period of time files may be in different formats, and
  
• Application programs may be in different languages.
  

So we can see there are problems with the straight file-processing approach:

• Data redundancy and inconsistency
  
  
  
  • Same information may be duplicated in several places.
    
  • All copies may not be updated properly.
    
  
  
• Difficulty in accessing data
  
  
  
  • May have to write a new application program to satisfy an unusual request.
    
  • E.g. find all customers with the same postal code.
    
  • Could generate this data manually, but a long job...
    
  
  
• Data isolation
  
  
  
  • Data in different files.
    
  • Data in different formats.
    
  • Difficult to write new application programs.
    
  
  
• Multiple users
  
  
  
  • Want concurrency for faster response time.
    
  • Need protection for concurrent updates.
    
  • E.g. two customers withdrawing funds from the same account at the same time - account has $500 in it, and they withdraw $100 and $50. The result could be $350, $400 or $450 if no protection.
    
  
  
• Security problems
  
  
  
  • Every user of the system should be able to access only the data they are permitted to see.
    
  • E.g. payroll people only handle employee records, and cannot see customer accounts; tellers only access account data and cannot see payroll data.
    
  • Difficult to enforce this with application programs.
    
  
  
• Integrity problems
  
  
  
  • Data may be required to satisfy constraints.
    
  • E.g. no account balance below $25.00.
    
  • Again, difficult to enforce or to change constraints with the file-processing approach.
    
  </LI>
  

These problems and others led to the development of database management systems. </LI>

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