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Introduction to Database Systems
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Origins of Databases

• c1455 Gutenberg invents printing. Explosive
  interest in publication of books (analogous with
  explosive growth of Web in early 1990s) leads to
  public libraries
• Libraries were first to introduce standards for
  information storage and retrieval
• These paper-based systems were extended and
  enhanced, and filing, indexing and classification
  schemes were developed
• Second World War accelerated RD in computing
  technologies spawned capability to computerise
  maintenance of records

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Computerised Data Storage

• Advantages of computerised data storage over
  paper-based systems include
• ability to store data compactly (e.g Britannica
  CD)
• enhanced data retrieval
• ability to access data remotely, e.g. from a
  mobile workstation, off-site location, or distant
  branch
• ability to share data amongst multiple users with
  concurrent access
• facility to automate regular, speedy back-ups
• enhanced data editing
• Most significant disadvantage is vulnerability
  e.g system crash, corrupted data, viruses,
  hackers, etc.

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Information A Vital Asset !

• Information is a vital organisational asset.
  Without accurate, current, relevant information,
  mistakes and misjudgements may be made
• Data management is an essential capability in the
  modern business environment / information society
• A knowledge organisation is one in which the
  primary asset is information its competitive
  advantage is derived from effective use of
  documented knowledge. Examples accounting firms,
  marketing companies, software houses
• Organisational memory extends and amplifies
  information / knowledge by capturing, organising,
  disseminating, and reusing it

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Organisational Information
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Organisational Information
Organisational memory
Data
Informed decisions
Improved products and services
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Attributes of Good Information

• Current
• Timely
• real-time systems are commonplace in modern
  business environment
• Relevant
• data is only useful if relevant to task in hand
• Shareable
• Complete
• Accurate and consistent

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Attributes of Organisational Memory

• Transportable
• authorised personnel should have access to data
  anywhere, anytime
• Secure against unauthorised access

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Organisational Information Systems

• Generally, there is an alignment between business
  units and core operational systems
• Typical core systems are
• Sales Marketing Department Customer management
  system, Order processing system
• Operations Unit Purchasing system, Inventory
  control system
• Finance Department Accounts payable and
  receivable systems, Credit Management system
• There are interdependencies between these
  systems hence the need for an integrated data
  management approach

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Whats it all about?

• Database systems facilitate the easy storage and
  retrieval of data
• Databases should be able to produce fixed format
  as well as ad hoc reports
• Its no good if all the data is in the system if
  you cant (easily) get it out !!!
• Example of manual paper-based system OLIS
  project
• Example A pair of spectacles were found by the
  cleaners in a lecture hall. We want to see a
  system-generated email to all students who were
  scheduled to be in that venue on the day in
  question. This requires us to be able to merge
  and aggregate data from course registration
  system, timetabling system, student contact
  details. A database can help !

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Data Storage

• Information systems create, read, update and
  delete data
• Data can be stored in conventional files or
  databases
• Files are collections of similar records
• Databases are collections of interrelated files.
• Records can be linked through specified
  relationships to records in other files

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Conventional Files

• In the file environment, data storage is built
  around the applications that will use the files
• Essentially, the file belongs to a specific
  application. This is termed program-data
  dependence
• As applications are developed, customised files
  are created which may be unusable by other
  applications

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Conventional Files

• First attempts at computerised storage of records
  followed traditional paper-based metaphors (Flat
  file systems)
• Flat files were inefficient for data retrieval
  it might be necessary to search entire file for a
  record (which, it may transpire, does not exist).
  Remedy index files
• Indexing improved data retrieval, but
  conventional files have other disadvantages
• Program-Data dependence
• Proprietary file formats (closed systems)
• Poor scalability

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Conventional Files

• Disadvantages (Contd)
• Duplicated and redundant data
• ambiguity same thing being referred to by
  different names in different places
• inconsistency conflicting / unsynchronised data
• wasted effort
• Separation and isolation of data
• data dispersed amongst many files complicates
  processing
• Inflexibility
• cumbersome data structures and report layouts
• not responsive to ad hoc queries
• excessive program maintenance
• Development environment
• procedural -v- non-procedural (3GL -v- 4GL)

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Conventional Files

• Advantages
• Historically, conventional files have been faster
  to process than DBMS applications
• As legacy file-based systems become candidates
  for reengineering, the trend is to replace them
  with database systems

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Database Management Systems

• A database is a large, integrated collection of
  data which models a real-world enterprise
• A Database Management System (DBMS) is
  a software package designed to store and manage
  databases
• In a DBMS environment, applications are built
  around an integrated adaptable database

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Database Management Systems

• Advantages
• ability to share the same data across multiple
  applications and systems
• data independence
• control of redundancy
• enforced data integrity
• improved data security
• uniform data administration
• concurrent access
• improved backup and recovery facility
• flexible data structures

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Database Management Systems

• Advantages (Contd)
• databases allow the use of the data in ways not
  originally specified by the end-users (ad hoc
  queries)
• database definition can be extended without
  impacting existing programs that use it
• economies of scale

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Database Management Systems

• Disadvantages
• database technology is more complex than file
  technology
• requires more sophisticated hardware and software
  (DBMS)
• DBMSs can still be slower than file-based
  systems
• database technology requires a significant
  investment
• database administration
• operating costs and ongoing maintenance
• end-user training
• higher impact of system failure

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Database Management Systems

• Roles in a DBMS environment
• Data Administrator
• Database Administrator
• Database Designer
• Application Programmer
• End-User