Information Systems &
2.3) Storage and Retrieval
• A database management system
(DBMS) is the software used to
access, create and modify a
• There are two main ways of
• processes in sequence
• slower than direct
• e.g. magnetic tape
• can go straight to data
• faster than sequential
• more expensive
• A distributed database is a database
located at more than one site.
• It reduces data transmission costs.
• They need to be synchronised often.
• There are many types of storage
media. They can include:
• hard disc – a disc made of metal or
glass and covered in a magnetic
material (hard drives)
• optical disc – a plastic disc with a
reflective metal layer (CD, DVD,
• magnetic tape – a long strip of
plastic coated with a thin layer of
magnetic material; they are
inexpensive and sequential in
• Encryption is the process of
• Decryption is the process of
changing it back.
• Encrypted data is an effective way
to ensure data security.
• There are two main kinds of
• asymmetric –require different
keys for encrypting and
• symmetric –uses the same keys
for encrypting and decrypting
A DBMS contains backup and
recovery capabilities to guard
against data loss.
A backup is another copy of the
data that can be used to rebuild
Ideally, the backup should be in a
secure and different location.
Data security measures can also
• user accounts and passwords
• personal ID objects like magnetic
• biometric devices (e.g. fingerprint
scan, voice recognition)
• firewall – mix of hardware & software
• offline data access – no Internet
• Sorting is the process or arranging the
data in meaningful way.
• Sorts can be either ascending or
• Ascending is:
• smallest to largest
• earliest to latest
• Descending is the reverse.
• Searching the database is performed
through constructing a query.
• A query is a search for records that
meet certain conditions (or criteria)
• A simple query is constructed in the
form of :
• A common method is called query by
• This is where you put characters into a
search field (with wildcards if needed)
• Wildcard characters represent one or
more unknown characters.
• An asterisk (*) substitutes for any
number of characters while a question
mark (?) substitutes for only one
• Operators represent the action that is
performed in the query.
• They can be either relational or logical.
• Relational operators are symbols
indicating the relationship between
• They include: >, <, =, <>, <=, >=
• Logical operators are used to combine
• They include AND, OR & NOT.
• AND requires each condition to be met
while OR will be satisfied with any
• E.g. Year = 10 AND Gender = “M” will
return only Year 10 males while Year =
10 OR Gender = “M” will give all the
males in the school and all of Year 10
• A query language is a specialised
language designed to search a
• Structured query language (SQL) is a
query language that uses the following
• ORDER BY
[COPY Table 2.4, p.59]
• When using SQL it is important to use
the correct syntax.
• This includes:
• keywords written in upper case
• fields separated by commas
• entity and attribute separated
by a full stop
• criteria or data items inside
quotation marks unless a
FROM students, classes
WHERE Year>10 AND Gender = “F”
ORDER BY lname [asc], fname [asc]
[Complete LA 2 (c) and (d), p.63]
• A search engine is a database of
• Indexing creates a table of information
about the location of data.
• This table is built by regularly scanning
the Internet for new sites and looking
at keywords and metadata.
• This scanning is often carried out by
programs called spiders, crawlers or