>>I am redesigning a system that currently uses two tables to record work done by a person. One table called "service" records work that is not related to a piece of equip. The other table is called "summary" for work done on equip. Tables are almost identical. I was thinking of combining these and setting the foreign key to the equip table to be null if the work does not relate to a piece of equip.
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>>Does this violate good relational design? I have heard the term "overloading" but can't find any references.
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>How identical are they? If summary is the same with just some added fields (i.e. all the common fields mean the same thing), then you could have summary as a child of service and only service records with children would be for equipment.

Two fields are different, so pretty darn close.