Beginning with version 1.3, it is possible to ``fine-tune'' the summary information generated by the Essence summarizers. A typical application of this would be to change the Time-to-live attribute based on some knowledge about the objects. So an administrator could use the post-summarizing feature to give quickly-changing objects a lower TTL, and very stable documents a higher TTL.
Objects are selected for post-summarizing if they meet a specified condition. A condition consists of three parts: An attribute name, an operation, and some string data. For example:
city == 'New York'
In this case we are checking if the city attribute is equal to the string `New York' The for exact string matching, the string data must be enclosed in single quotes. Regular expressions are also supported:
city ~ /New York/
Negative operators are also supported:
city != 'New York' city !~ /New York/
Conditions can be joined with `
&&' (logical and) or
||' (logical or) operators:
city == 'New York' && state != 'NY';
When all conditions are met for an object, some number of instructions are executed on it. There are four types of instructions which can be specified:
time-to-live = "86400"
keywords | tr A-Z a-z
address,city,state,zip ! cleanup-address.pl