Introduction to File Processing
with PHP
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.
File Structures
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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 -> Column
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 further
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
placed
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 blocks
• Modification: do not allow records to cross block boundaries
• Ways to delete record i:
• move records i + 1, . . ., n
to i, . . . , n – 1
• move record n to i
• do not move records, but
mark deleted record
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 records
Sequential File Organization
• For sequential processing of entire file
• Records ordered by a search-key
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 order
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 file
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 languages
The PHP filesystem functions
• http://us2.php.net/manual/en/ref.filesystem.
php
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.php
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