Depending on what you mean, I'd say datalog is partially characterized as compared to prolog by it's lack of unification (also it's typically executed bottom up

Depending on what you mean, I'd say datalog is partially characterized as compared to prolog by it's lack of unification (also it's typically executed bottom up and sometimes considered to not have compound terms). Unification is roughly bidirectional pattern matching whereas datalog rules are in essence performing unidirectional pattern matching / query on a database.