Read the summary and the most important questions on Databases

• Database Systems: Concepts & Definitions

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• What is a file-based system?

  •collection of application programs that perform services for the end users (e.g. reports).
  
  
  •each program defines and manages its own data

• What are 5 limitations of a file-based approach?

  
  
  
  
  • Separation and isolation of data
  
  
  – Each program maintains its own set of data.
  
  
  – Users of one program may be unaware of potentially useful data held by other programs.
  
  
  
  
  • Duplication of data
  
  
  – Same data is held by different programs.
  
  
  – Wasted space and potentially different values and/or different formats for the same item. 
  
  
  
  
  
  
  • Data dependence – File structure is defined in the program code.
  
  
  
  
  • Incompatible file formats
  
  
  – Programs are written in different languages, and so cannot easily access each other’s files.
  
  
  
  
  • Fixed Queries/Proliferation of application programs
  
  
  – Programs are written to satisfy particular functions. – Any new requirement needs a new program. 
  

• What is a database?

  “a shared collection of logically related data (and a description of this data), designed to meet the information needs of an organisation”.

• Regarding an organisations information, what does data comprise of?

  Entities, attributes and relationships

• What is the relation data model?

  The primary data model for data storage and processing
  - The model is simple and has the capabilities to process data with storage efficiency
  
  --> relations are saved in the form of tables
  
  (more on this in next lecture)

• What are the primary functions of a DBMS?

  
  
  
  
  • adatalanguage
  – for defining and updating databases – for retrieving data
  
  
  • asecuritysystem
  • adataintegritysystem
  • aconcurrencycontrolsystem • arecoverycontrolsystem
  • a user-accessible catalog 

• What are the advantages of a DMBS?

  • Control of data redundancy
  • Data consistency
  • More information from the same amount of data
  • Sharing of data
  • Improved data integrity
  • Improved security
  • Enforcement of standards
  • Economy of scale
  • Balanced conflicting requirements
  • Improved data accessibility and responsiveness 
  • Increased productivity 
  • Improved maintenance through data independence
  • Increased concurrency
  • Improved backup and recovery services

• What are the disadvantages of a DMBS?

  • Complexity
  • Size 
  • Cost
  • Additional hardware costs
  • Cost of conversion
  • Performance
  • Higher impact of a failure

• The Relational Data Model

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• What is the definition of relational database?

  A collection of normalised tables with distinct names

• How many values does a cell contain? What term is used for this?

  Each cell contains one value i.e. it it atomic