Subject Descriptor in a paper?
In an academic paper, we can often see such works below abstract:

> Subject Descriptors:

> C5 Computer System Implementation

> G2.2 Graph Algorithms

Does every paper need this? Where can I find complete list of these categories?

Subject Descriptor in a paper?
===

In an academic paper, we can often see such works below abstract:

> Subject Descriptors:

> C5 Computer System Implementation

> G2.2 Graph Algorithms

Does every paper need this? Where can I find complete list of these categories?
