this fashion of or-parallelism arises whenever the different alternatives in a parallel choice-point are independent of each others--i.e., no two alternatives belonging to a choice-point access the same conditional variables. The most common instance of independent or-parallelism occurs when the query which originates or-parallelism is ground, i.e. it does not contain any unbound variable.
Independent or-parallelism has the advantage of not requiring any change to the environment representation scheme adopted in standard sequential implementations. The amount of effort required to design a system exploiting independent or-parallelism is minimal, and guarantees a very high level of efficiency (overhead is limited). On the other hand, its applicability is quite limited (typical example queries with all ground arguments).
Another example of independent or-parallelism comes from the area of deductive databases. One of the most commonly used approaches to parallelization of Datalog programs is based on the concept of Decomposability [121, 120]. The notion can be synthesized as follows: given the set of all possible derivable ground atoms and the Extensional database E, the program is decomposable if there exists a partition of such that, if and can be proved from the program, then the derivation tree of g contains only atoms from . This notion allows partitioning of the database between different processors, with the guarantee that the computation of a query can be carried on in a processor without the need of any communication. This form of parallelism can be seen as another instance of the independent or-parallel model.