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File Processing System

File Processing System

 

A File can store records and we can extract these records using different applications programs.

  • The simplest data retrieval task from file require extensive programming. Also this is a time consuming and a high skill activity.
  • To access the data in file  the programmer must aware of the physical structure of the file.
  • Security features such as effective password protection, locking parts of file etc are very difficult to program.
  • The File system exhibits structural dependence. That is a change in  file structure such as addition or deletion of a  field require the modification of all programs using that file.
  • Data dependence: A change in file data characteristic such as change in a field  data type from integer to decimal, requires changes in all programs that access the file.

A typical file processing system is supported by conventional operating systems. The system stores permanent record in various files. It uses various application programs to extract records from, and add records to the appropriate files. Before using DBMS to store and retrieve data, organizations  stored information in file processing systems.

But as the number of files in the system expands, system administration becomes difficult too. Each file must have its own file management system, composed of programs that allow user to create the file structure, add data to the file, delete data from the file, modify the data in the file, list the file contents etc.

Even a simple file processing system containing 25 files requires 5 * 25 =125 file management programs. Each department in the organization owns its data by creating its own files. So the number of files can multiply rapidly.

Security features such as effective password protection, locking out part of files or part of system itself and other data confidentiality measures are difficult to program and are usually omitted.

The file system’s structure and lack of security makes it difficult to pool data. The same basic data is stored in different locations. But it is very unlikely that that data stored in different locations will always be updated consistently, hence maintaining different versions of same data. The file processing system is simply not suitable for modern data management and  information requirement.

Functional Dependency in RDBMS

Functional Dependency

  • Functional Dependency
  • Full Functional Dependency
  • Partial Dependency
  • Transitive Dependency

Functional Dependency:
Given a Relation R(A,B,C,D), Where A,B,C,D are attributes.

Functional Dependencies A→BCD , BC→D .

A→BCD means A functionally determines BCD.
BC→D means BC functionally determines D.

Full Functional Dependency:
Given a relation R and Functional Dependency X→Y
Y is fully functionally dependent on X and there should not be any Z→Y, Where Z is a proper subset of X.


Partial Dependency:
If any proper subsets of the key determine any of the non-key attributes then there exist a partial dependency.

Example: Given a relation R(A,B,C,D,E) , Functional Dependency : AB→CDE , Primary_key(or simply 'key') is AB.

Then    A→C : is a Partial Dependency
            A→D :  is a Partial Dependency
            A→E : is a Partial Dependency
            B→C : is a Partial Dependency
            B→D : is a Partial Dependency
            B→E : is a Partial Dependency


Transitive Dependency

 Given a relation R(A,B,C,D,E)  then dependency like A-->B, B-->C   is a transitive dependency, since   A-->C is implied .

 

3NF Third Normal Form in RDBMS

3NF Third Normal Form
A relation R is in 3NF if it is in 2NF and has no transitive dependency.Here all the non-key attributes are depend on the key alone.There should not be any dependency among the non-key attributes.

 

Transitive Dependency

 Given a relation R(A,B,C,D,E)  then dependency like A-->B, B-->C   is a transitive dependency, since   A-->C is implied .

Partial Dependency in RDBMS

Partial Dependency:


If any proper subsets of the key determine any of the non-key attributes then there exist a partial dependency.

Example: Given a relation R(A,B,C,D,E) ,

Functional Dependency : AB→CDE ,

Primary_key(or simply 'key') is AB.

Then    A→C : is a Partial Dependency
            A→D :  is a Partial Dependency
            A→E : is a Partial Dependency
            B→C : is a Partial Dependency
            B→D : is a Partial Dependency
            B→E : is a Partial Dependency

2NF Second Normal Form in RDBMS

2NF Second Normal Form
A relation R is said to be in 2NF if it is in 1NF and there should not be any partial dependency.

Here all the non key attributes are dependent on the key alone. No  attribute is depend upon a part of the key.

Any relation having a key with single attribute is in 2NF.

 

Partial dependency in RDBMS

Partial dependency exist if any non key attribute functionally depend upon a part of the key.