Garbage (computer Science) - Classification

Classification

Garbage is generally classified into two types:

semantic garbage

Semantic garbage is any object or data which will never be accessed by a running program, for any combination of inputs to the program.

syntactic garbage

Syntactic garbage refers to objects or data within a program's memory space that are unreachable from the program's root set.

Note that syntactic garbage is a (usually strict) subset of semantic garbage as it is entirely possible for an object to hold a reference to another object without the latter object being used. Determination of the semantic garbage present in a program is generally undecidable, but there are many algorithms for identifying syntactic garbage.

Objects and/or data which are not garbage are said to be live.