The document discusses data persistency and different methods for achieving it. It defines persistence as the ability of data to outlive the execution of the program that created it. Common ways to achieve persistence include saving data in files or using cookies and sessions with PHP to store data across HTTP requests since HTTP is a stateless protocol. The document also distinguishes between persistent data, which is infrequently accessed and not likely to be modified, and dynamic data which is asynchronously updated.

1. Data Persistency
Subject:
Web Engineering
Presented by :
Umer Farooq
Bs-IT- (3049)
Evening -5th
University of Education okara ,Renala
Campus1

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
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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
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4. 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.
Data Persistency
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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
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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
serverClient
Cookie
Session
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