Variable length file header apparatus and system

Abstract

Ensuring that a user obtains a correct version of a file, wherein the file includes a file header section and a data section, is disclosed. Expiration information is inserted in the file header by a first application. The expiration information is extracted from the file header by a second application. An expiration date for the file is determined from the extracted expiration information. The determined expiration date is compared with a comparison date, and use of the file is disallowed if the comparison determines that the file has expired.

1 . A method of ensuring that a user obtains a correct version of a file, wherein the file includes a file header section and a data section, comprising; 
 extracting expiration information from the file header with a second application, wherein the expiration information was inserted in the file header with a first application;    determining an expiration date for the file from the extracted expiration information; and    comparing the determined expiration date with a comparison date;    wherein use of the file is disallowed if the comparison determines that the file has expired.    
   
   
       2 . The method of  claim 1 , wherein extracting includes: 
 reading a data tag from a field in the file header;    determining whether the data tag is a file expiration data tag; and    if the data tag is a file expiration data tag, reading expiration information from the field.    
   
   
       3 . The method of  claim 2 , wherein the expiration information read from the file includes a date.  
   
   
       4 . The method of  claim 2 , wherein the expiration information read from the field includes an integer.  
   
   
       5 . The method of  claim 4 , wherein determining an expiration date includes adding the integer read from the field to a date obtained from another source.  
   
   
       6 . The method of  claim 5 , wherein the date obtained from another source is a date read from a different field in the file header.  
   
   
       7 . The method of  claim 5 , wherein the date obtained from another source is a date obtained from another file.  
   
   
       8 . The method of  claim 1 , wherein the comparison date is a system date on a computer.  
   
   
       9 . A system for ensuring that a user obtains a correct version of a file, wherein the file includes a file header section and a data section, comprising: 
 a processor; and    a memory coupled with the processor, wherein the memory is configured to provide the processor with instructions which when executed cause the processor to: 
 extract expiration information from the file header, wherein the expiration information was inserted in the file header with a first application;  
 determine an expiration date for the file from the extracted expiration information; and  
 compare the determined expiration date with a comparison date;  
 wherein use of the file is disallowed if the comparison determines that the file has expired.  
   
   
   
       10 . The system recited in  claim 9 , wherein extracting includes: 
 reading a data tag from a field in the file header;    determining whether the data tag is a file expiration data tag; and    if the data tag is a file expiration data tag, reading expiration information from the field.    
   
   
       11 . The system of  claim 10 , wherein the expiration information read from the file includes a date.  
   
   
       12 . The system of  claim 10 , wherein the expiration information read from the field includes an integer.  
   
   
       13 . The system of  claim 12 , wherein determining an expiration date includes adding the integer read from the field to a date obtained from another source.  
   
   
       14 . The system of  claim 13 , wherein the date obtained from another source is a date read from a different field in the file header.  
   
   
       15 . The system of  claim 13 , wherein the date obtained from another source is a date obtained from another file.  
   
   
       16 . The system of  claim 9 , wherein the comparison date is a system date on a computer.  
   
   
       17 . A computer program product for ensuring that a user obtains a correct version of a file, wherein the file includes a file header section and a data section, the computer program product being embodied in a computer readable medium and comprising computer instructions for: 
 extracting expiration information from the file header with a second application, wherein the expiration information was inserted in the file header with a first application;    determining an expiration date for the file from the extracted expiration information; and    comparing the determined expiration date with a comparison date;    wherein use of the file is disallowed if the comparison determines that the file has expired.    
   
   
       18 . The computer program product of  claim 17 , wherein extracting includes: 
 reading a data tag from a field in the file header;    determining whether the data tag is a file expiration data tag; and    if the data tag is a file expiration data tag, reading expiration information from the field.    
   
   
       19 . The computer program product of  claim 18 , wherein the expiration information read from the file includes a date.  
   
   
       20 . The computer program product of  claim 18 , wherein the expiration information read from the field includes an integer.  
   
   
       21 . The computer program product of  claim 20 , wherein determining an expiration date includes adding the integer read from the field to a date obtained from another source.  
   
   
       22 . The computer program product of  claim 21 , wherein the date obtained from another source is a date read from a different field in the file header.  
   
   
       23 . The computer program product of  claim 21 , wherein the date obtained from another source is a date obtained from another file.  
   
   
       24 . The computer program product of  claim 17 , wherein the comparison date is a system date on a computer.