depending on the departmentspecific SKU profiles and storage technology
6. Conclusions and discussions
The distribution of the research results among
the various warehouse operational problems is
shown in Fig. 1, where the numbers in parentheses
represent the number of papers addressing the
corresponding problem. It is clear that the past
research has focused strongly on storage and order
picking. This is not surprising since these are the two
warehouse functions that have the largest impact
on the overall warehouse operational performance including
storage capacity, space utilization, and order picking effciency.
On the other hand, the development of research
is not well balanced. Some problems received far
more attention from the research community than
others. For example, the SLAP and routing
problems account, respectively, for 32% and 38% of
the total surveyed literature, while zoning accounts
for less than 6%. Furthermore, there is little direct
evidence of collaboration of the academic research
community with industry. Many of the research
results are not sufficiently communicated to
industry to make a significant impact on the practice
of warehouse operations. More communication from
both sides might help to better identify the real
challenges faced in warehouse operations, to appreciate
the opportunities for better operation, and to realize
these opportunities by close cooperation between
researchers and practitioners.
The problems discussed in this paper are at the
operational level, which means that decisions need
to be made quite frequently and the influence of
these decisions is typically of a short duration and
localized. Such decisions typically need to be made
quickly without extensive computational resources.
This tends to encourage the use of heuristic
procedures that can find a good solution reliably in a
reasonable amount of time. In addition, from the
management point of view, an ideal solution
method should be simple, intuitive, and reliable in
order to minimize the training costs in the warehouse.
Another consequence of the operational nature
of the problems discussed in this paper is that
the problems should be considered dynamically by
constantly incorporating new information about the
operating environments. Some research on the
dynamic planning of warehouse operations exists,
but the dynamic problems are much less studied
than the equivalent static problems. Furthermore,
research in the literature usually concentrates on
certain standard performance measures, such as
the total order picking cost. In many practical situations,
different objectives such as the tardiness, or the order
cycle time, are as important as the traditional aggregate
performance measure.
In summary, there continues to be a need for
research focusing on the operational management
of warehousing systems, where the different
processes in the warehouse are considered
jointly, the problems are placed in their dynamic nature, and
multiple objectives are considered simultaneously.
Clearly, the research domain of warehouse
operations is very rich and challenging.
Given the prevalence of warehouses
in the supply chains, such research results
can have a significant economic impact.