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Summary A* 9618 Chapter 8: Databases
8.1 Database concepts 8.2 Database management system (DBMS) 8.3 DDL and DML Helped me get A*
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8 Databases8.1 Database concepts
Show understanding of the limitations of using a file-based approach
for the storage and retrieval of data
Data stored in discrete files, stored on computer, and can be accessed,
altered or removed by the user.
Limitations of File Based System:
No enforcing control on organisation/structure of files
Data Redundancy:
Data repeated/duplicated in different files
manually change each
Inconsistent data
Memory wastage
Fixed queries
Programs are written to satisfy particular functions
Sorting must be done manually or must write a new program
Incompatible file formats
Data may be in different format; difficult to find and use other
files.
Impossible for it to be multi-user; chaotic
Security not sophisticated
users can access everything
Each user should only be allowed to access data concerning
their requirements only.
8 Databases 1
, Describe the features of a relational database that address the
limitations of a file-based approach
In a file-based approach, the record structure is fixed, however, in a
relational database, attributes can easily be added/deleted.
Relational databases have a query generator which can reduce the time
taken to produce a new query, in a file-based approach a new program
must be created to produce a query.
Reduced data redundancy/duplication
Data is stored in separate linked tables
Reduced data dependency
Program-data independence
Changes to the data(design) do not require changes to
programs.
E.g. fields can be added or removed without effecting existing
programs
Improved data integrity
Data only needs to be updated once/is only stored once which
also improves data consistency.
The DBMS uses its data dictionary to perform validation checks
on data entered.
Improved security
Each user can be given access rights so it can only access the
data it needs.
Data privacy is maintained.
Complex queries are easily done
Complex queries can be more easily made as the DBMS will
have a query language
Ability to create ad hoc queries
Allow concurrent access
8 Databases 2
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