Slide 6.1: Record access

Record Access

When looking for an individual record, it is convenient to identify the record with a key based on the record's contents.

A key is a value used to identify a record in a file, derived by applying some fixed function to the record. The key is often simply one of the fields.

A Sequential Search
A sequential search reads through the file, record by record, looking for a record with a particular key. Assume the file Sequential.txt is

File Structures:     An Object-Oriented Approach with C++ |0201874016|94.80|360|
 Learning WML   &   WMLScript |1565929470|17.48|12|
      XML in a Nutshell,     2nd Edition|0596002920|39.95|39|
  Java and XSLT |0596001436|26.37|890|
WAP Servlets:   Developing Dynamic Web Content With Java and WML|047139307|32.99|4|
   WAP Development with WML and WMLScript|0672319462|18.99|56|
Advances in Security and Payment Methods for Mobile Commerce|1591403456|89.95|182|
M Commerce:   Technologies, Services, and Business Models |0471135852|23.09|5|
 Mobile       Commerce                 |0521797561|29.51|93|
Dynamic WAP Application Development     |1930110081|34.59|18|

where

each record is with a variable length,
each record has four fields: title, ISBN, price, and quantity,
the character ‘|’ is the field delimiter, and
each record is ended with a newline ‘\n’.

The following interface requests users to select a language and enter a URL and a key ISBN to find the record with the specified ISBN in the file.

Select a Language and Enter a URL and an ISBN to Access the Record.
Language: C++ Unix shell URL: ISBN:
Password: