If users may need the facts at both a detailed and an aggregate level, but the detailed data users are few and the storage costs are of concern, plus the circumstance is such that dividing the aggregated data is relatively easy, then one can consider lumping and keeping the fact table at an aggregate level. Fact table grain is likely the best case for observing these choices. However, circumstances certainly arise where inside an application one or the other approach is more effective. Statis is an unlikely goal, as it does not seem possible that anyone can ever convincingly state that “Splitting is always best” or that “Lumping is eternally the most useful choice.” And in practice, proper and useful solutions are built using one or the other, or more often, a hybrid of splitting and lumping decisions along the way. The question to split or lump arises across many kinds of choices, in addition to the entity definition, table grain, or the domain grain mentioned in the previous examples this issue is at the heart of deliberations regarding establishing functions, overriding methods, or composing an organizational structure.Įinstein once stated that “Reality is merely an illusion, albeit a very persistent one.” If reality is but an illusion, then whether one splits or one lumps really is of little concern. The split-versus-lump issue is ubiquitous and universal. This debate underlies much of the decision-making involved in determining what domains to create within a data model. Or perhaps lumping is discussed as the grain of a multidimensional fact is proposed. Within data modeling, arguments arise, such as whether to sub-type an entity. On the other side of the design fence, lumpers combine items until everything is abstracted into group objects covering very broad territory, such as a “Party” construct, or ultimately an “Object” object. Splitters take a group of items divide them up into sub-groups and sub-sub-groups occasionally going so far as to end with each lowest level becoming a group of one. Design battles are waged across conference rooms as debates rage over whether to split or to lump. The whole world can be divided into two groups, these being splitters and lumpers.
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