The system may immediately transform the downloaded file avail.txt into the following file avail1.txt:
-1 531
76 12 File Structures: An Object-Oriented Approach with C++|0201874016|94.80|360|
46 100 Learning WML & WMLScript|1565929470|17.48|12|
52 158 XML in a Nutshell, 2nd Edition|0596002920|39.95|39|
36 222 Java and XSLT|0596001436|26.37|890|
82 270 WAP Servlets: Developing Dynamic Web Content With Java and WML|047139307|32.99|4|
60 364 WAP Development with WML and WMLScript|0672319462|18.99|56|
83 436 Advances in Security and Payment Methods for Mobile Commerce|1591403456|89.95|182|
76 531 M Commerce: Technologies, Services, and Business Models|0471135852|23.09|5|
where
- Each of the
head/last/offsets takes five bytes.
- The first record is
head+' '+last+'\n' where head is the head (offset) of the avail list and last is the offset of the last record.
- For the remaining records, each record begins with
length+' '+offset+' ' where
- the
length is the actual record length including '\n' but not including the length+' '+offset+' ' , and
- the
offset is the disk offset right before the length.
After processing for a while, the file may become the following file avail2.txt:
222 531
76 12 File Structures: An Object-Oriented Approach with C++|0201874016|94.80|360|
46 100 *|-1 WML & WMLScript|1565929470|17.48|12|
52 158 XML in a Nutshell, 2nd Edition|0596002920|39.95|39|
36 222 *|436 XSLT|0596001436|26.37|890|
82 270 WAP Servlets: Developing Dynamic Web Content With Java and WML|047139307|32.99|4|
60 364 WAP Development with WML and WMLScript|0672319462|18.99|56|
83 436 *|100 in Security and Payment Methods for Mobile Commerce|1591403456|89.95|182|
76 531 M Commerce: Technologies, Services, and Business Models|0471135852|23.09|5|
where the asterisk * means the record is deleted. These file structures were discussed in the previous slides.
†Note that the above file structures are designed by the instructor.
Various other file structures are available or can be designed.