  Efficiency techniques are an integral part of Entity Resolution, since its
infancy. In this survey, we organized the bulk of works in the field into
Blocking, Filtering and hybrid techniques, facilitating their understanding and
use. We also provided an in-dept coverage of each category, further classifying
the corresponding works into novel sub-categories. Lately, the efficiency
techniques have received more attention, due to the rise of Big Data. This
includes large volumes of semi-structured data, which pose challenges not only
to the scalability of efficiency techniques, but also to their core
assumptions: the requirement of Blocking for schema knowledge and of Filtering
for high similarity thresholds. The former led to the introduction of
schema-agnostic Blocking in conjunction with Block Processing techniques, while
the latter led to more relaxed criteria of similarity. Our survey covers these
new fields in detail, putting in context all relevant works.
