There are three key concepts in Zend_Cache. One is the unique
identifier (a string) that is used to identify cache records. The second one is the
'lifetime' directive as seen in the examples; it defines for how long
the cached resource is considered 'fresh'. The third key concept is conditional execution so
that parts of your code can be skipped entirely, boosting performance. The main frontend
function (e.g. Zend_Cache_Core::get()) is always designed to return
FALSE for a cache miss if that makes sense for the nature of a
frontend. That enables
end-users to wrap parts of the code they would like to cache (and skip) in
if(){ ... } statements where the condition is
a Zend_Cache method itself. On the end if these blocks you must save
what you've generated, however (e.g. Zend_Cache_Core::save()).
Note
The conditional execution design of your generating code is not necessary in some frontends (Function, for an example) when the whole logic is implemented inside the frontend.
Note
'Cache hit' is a term for a condition when a cache record is found, is valid and is 'fresh' (in other words hasn't expired yet). 'Cache miss' is everything else. When a cache miss happens, you must generate your data (as you would normally do) and have it cached. When you have a cache hit, on the other hand, the backend automatically fetches the record from cache transparently.