AC1103 Information Technology

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AC1103Information Technology

• Databases
• Lecture 1 of 4

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What we will cover...

• Theory of databases
• Relational databases
• Design of relational databases
• Use of MS Access 97

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Databases
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What is a Database?

• A database is any collection of data of a similar
  nature, such as
• address book
• library catalogue
• telephone directory
• Yellow Pages
• Usually the data is ordered in some way.

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What is a database for?

• A database is used for the storage of
  information.
• It is also important to be able to retrieve
  certain data rapidly from the database.

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Why use a computerised DB?

• Using a computerised database is desirable for
  several reasons
• physical storage is smaller (e.g. 600MB on
  CD-ROM)
• computer is good at retrieval (fast and
  efficient)
• complex data entities can be stored and accessed
  easily

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The components of a DB
Data
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The components of a DB
Data
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The components of a DB
Database Management System
Data
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The components of a DB
Database Management System
Data
Database System
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Summary

• A Database Management System (DBMS) is the
  application program used to access and maintain
  the database.
• However, the term database is commonly used to
  refer to the DBMS, or the DBMS and the data
  together!

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Why use a DBMS?

• Semantic problems
• users may use different terms
• Data sharing
• why duplicate data?
• Data integrity
• is all data valid?

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Why use a DBMS?

• Data isolation
• compatible datae.g. Mar99 vs 03/99
• Data redundancy
• why store multiple copies?
• Data inconsistency
• is same data updated together?

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Facilities of a DBMS

• Concurrent Access
• Crash Recovery
• Data Security

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Databases

• Online databases - user accesses existing,
  often using a custom interface, such as
• Dynix library catalogue
• databases on CD-ROM
• databases on the Internet

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Databases

• User databases - user creates the database and
  maintains the data using a system such as
• MS Cardfile
• MS Works
• MS Access

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Types of Database

• Flat file
• (simple data only)
• Relational
• (also network, hierarchical)
• (complex data)

Simple
Complex
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Flat file database
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Records and Fields

• Information about each object forms a record in
  the database.
• Each item of information within a record is
  called a field.
• e.g. in a telephone directory, each subscriber
  has a record, name is a field, address is a
  field, phone number is a field, etc.

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Records and Fields
Fields Surname Name Phone Number
Record 1 Waller Annalu 344080 Record
2 Hussain Amir 345054 Record 3 Peiris Ramanee
345196
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Form View

• Each record can be viewed individually, with each
  field name and the corresponding field data.
• This looks like a filled-up form!

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List View

• All records have the same fields, so we can view
  the data as a list
• column headers are field names
• each row is a record
• each data field forms a cell

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Report View

• Most often, a subset of data is required from the
  database is, presented in a neat manner.
• A report view can be created to display parts of
  the database, using custom formatting, including
  sorting.

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Form View
Surname Phone Number
Waller 345080 Hussain 345054 Peiris 345196
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Sorting the Data

• Database programs allow stored data to be easily
  sorted into
• alphabetical order
• numerical order
• date order
• (ascending or descending order)

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Form View
Surname Phone Number
Hussain 345054 Peiris 345196 Waller 345080
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Using a Database

• A database is used differently to a word
  processor or spreadsheet
• set up phase structure of the database and
  formatting options are stored initial data
  entered
• live phase database is used (retrieval) and
  data is kept up-to-date (editing)

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Real Databases

• All of the features we have seen would be
  included in any database program.
• We will start by looking at a simple real
  database - a flat file database.

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Flat File Databases

• A flat file database is analogous to a file of
  index cards
• each card holds data for a different (real world)
  object
• the items of information stored about each object
  are the same

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Flat File Databases

• A flat file database is can only deal with one
  list of data at a time.
• There is no limit to the number of records which
  can be stored.
• There is a limit to the number of fields which
  can be included (i.e. the complexity of the
  data)

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Cardfile

• MS Cardfile is a standard Windows accessory
  program.
• It is a very simple flat file database, presented
  like a conventional file of index cards.

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SUMMARY

• Databases store records made up from a series of
  fields
• Can view one record in form view
• Can view all records in list view
• Can create custom report views
• Can query and sort the database
• Simplest is the flat file database - only one
  list of simple data

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