# Similarity web interface instructions

Enter the terms or Concept Unique Identifiers (CUIs) whose similarity or relatedness you wish to compute into the fields labeled Term 1 and Term 2. You can enter any combination of terms or CUIs. For example:

1. heart attack and skull
2. C0018563 and C0037303
3. hand and C0037303

You can than either calculate the two terms similarity or relatedness. Semantic similarity measures quantify how ``alike'' (or similar) two concepts are by determining their closeness in a hierarchy. Semantic relatedness measures quantify the degree of semantic feature overlap between two terms. Two terms may be related (needle-thread) but not necessarily similar.

To calculate the similarity you have two options:

1. SAB which designates what UMLS source to obtain the hierarchical information
2. REL which designates what relation information to use from the designated source

To calculate hte relatedness you also have two options:

1. SABDEF which designates what UMLS sources to obtain the definitions from
2. RELDEF which designates what relations to use to create the extended definiton