Data Persistency

1
Data Persistency

• Subject
• Web Engineering
• Presented by
• Umer Farooq
• Bs-IT- (3049)
• Evening -5th

2
Introduction

• One of the most critical tasks that applications
  have to perform is to save and restore data
• Persistence is the storage of data from working
  memory so that it can be restored when the
  application is run again
• The choice of persistence method is an important
  part of the design of an application

3
Persistence

• Persistence is the ability of data to outlive the
  execution of the program that created them.
• An obvious way of achieving persistence is to
  simply save the data in a file

4
Data Persistency
Persistent Data denotes information that is
infrequently accessed and not likely to be
modified. The opposite of this is dynamic data
(also known as transactional data) where
information is asynchronously changed as further
updates to the information become available.
Updates to dynamic data may come at any time,
with periods of inactivity in between.
5
The need for persistence

• Consider these examples
• Counting the number of hits on a website
• i.e. how many times does a client load your web
  page source
• The questionnaire on computing experience
• Somehow your .php needs to remember previous
  instances of it being requested by a client

6
Persistence and HTTP

• Recall http is a stateless protocol. It
  remembers nothing about previous transfers
• Two ways to achieve persistence
• PHP cookies
• PHP sessions

HTTP server
Client
Session
Cookie