Introduction to File Processing with PHP - PowerPoint Presentation

Slide1

Introduction to File Processing with PHP

Slide2

Review of Course

Outcomes

1

. Implement file reading and writing programs using PHP.

2. Identify

file access schemes,

including:

sequential

file access

direct file access

indexed

sequential file access.

3. Describe file-sorting and file-searching techniques.

4. Describe data compression and encryption techniques.

5. Design a rational database using E-R modeling techniques.

6. Build a relational database.

7. Write database queries using SQL.

8. Implement a web-based relational database using MySQL. Slide3

File Structures

File Structures are

persistent

data structures

Files composed of records

Records composed of fields

Files can be viewed as tables

File

->

Table

Record

->

Row

Field

->

ColumnSlide4

File Organization

The

data

is stored as a collection of

files

. Each file is a sequence of

records.

A record is a sequence of

fields

.

One approach:

assume record size is fixed

each file has records of one particular type only

this

case is easiest to implement;

we will

consider

it furtherSlide5

Organization of Records in Files

Heap

– a record can be placed anywhere in the file where there is space

Sequential

– store records in sequential order,

perhaps based

on the value of the search key of each record

Indexing –

Keep two files, the Data File and an Index File and the data file. Index records hold file pointers of Data records

Hashing

– a hash function computed on some attribute of each record; the result specifies in which block of the file the record should be placedSlide6

Fixed-Length Records

Simple approach:

Store record

i

starting from byte

n

 (

i

–

1), where

n

is the size of each record.Record access is simple but records may cross blocksModification: do not allow records to cross block boundariesWays to delete record i: move records i + 1, . . ., n to i, . . . , n – 1move record n to ido not move records, but mark deleted recordSlide7

Variable-Length Records

Variable-length records arise in database systems in several ways:

Storage of multiple record types in a file.

Record types that allow variable lengths for one or more fields such as strings

Record types that allow repeating fields (used in some older data models).

We won’t talk about VL recordsSlide8

Sequential File Organization

For sequential processing of entire file

Records ordered by a search-keySlide9

Sequential File Organization

Deletion – use pointer chains

Insertion –locate the position where the record is to be inserted

if there is free space insert there

if no free space, insert the record in an overflow block

In either case, pointer chain must be updated

Need to reorganize the file from time to time to restore sequential orderSlide10

The CRUD paradigm

Open the current version of a file

Process it using the CRUD operations

Create records

Retrieve records

Update records

Delete records

Output and close the new version of the fileSlide11

Implementing CRUD paradigm in PHP

Use PHP file functions

There a many of them

We will start with a simple subset that are similar to file functions used in C and in other C-based languagesSlide12

The PHP filesystem

functions

http://us2.php.net/manual/en/ref.filesystem.phpSlide13

A C-like subset

fopen

http://us2.php.net/manual/en/function.fopen.php

fgets

http://us2.php.net/manual/en/function.fgets.php

fwrite

http://us2.php.net/manual/en/function.fwrite.php

fclose

http://us2.php.net/manual/en/function.fclose.phpSlide14

Some PHP File Tutorials

http://www.tizag.com/phpT/files.php

http://php.about.com/od/advancedphp/ss/php_read_file_5.htm

http://www.codingunit.com/php-tutorial-file-handling