Logic and Caching

The common use of the word logic says ‘Something that makes sense’. In mathematics, logic is the study of true and false. Logic uses operators to combine combinations of trues’ and falses’. Depending on the order of operators and variables (t/f), a final result of True or False, Yes or No, 1 or zero can be established.

Operators:

The 3 most common operators are AND OR NOT.

AND

Say to get a true outcome you need two variables to be true. We call the variables a and b. We can say outcome c needs a AND b. (True AND False) is equivalent to False.

OR

If an outcome only requires one of a number of variables to be true, we can say they are OR’ed. If we have 2 variables then if one other or both are true, the result is true. Normal language ‘or’ is actually an XOR, meaning one but only one.

NOT

Not simply negates the variable. NOT true is false, NOT false is true. Not is sometimes called the complement.

XOR

This means one or the other but not both. T XOR T is F, T XOR F is T.

How is this related to WinGate?

WinGates’ rules and caching are logic based. Look at the ‘What to Purge’ Tab on the caching properties. You will see a Tree control. This is how WinGate decides what to delete from the cache when it gets to big, or a manual purge is initiated. There are two levels in this tree. The lower level are the filters, shown as little books. These are OR’ed. Logically speaking if a file matches one of the filters, it will be deleted. Therefore if you add more filters, you will delete more files. Any file has only to match one filter to be deleted, it might match 1, 2, several or all of the filters, but as long as it matched one, it will be deleted. Filters on there own however do little. To give them structure, you have to add criteria. These are displayed as document icons. Criteria are AND’ed. This means that all the criteria in a filter must apply for a filter to apply. So if a file does not match all the criteria of a filter is not deleted by that filter. However, if it matches any filter, it will be deleted.

It works like this

Does a file match ALL the criteria of ANY filter. If yes then delete.