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{{Refimprove|date=May 2009}}
{{short description|Programming technique}}
'''Object–relational is a mapping''' ('''ORM''', '''O/RM''', and '''O/R mapping tool''') in [[computer science]] is a [[Computer programming|programming]] technique for converting data between incompatible [[type system]]s using [[object-oriented]] programming languages. This creates, in effect, a "virtual [[object database]]" that can be used from within the programming language. There are both free and commercial packages available that perform object–relational mapping, although some programmers opt to construct their own ORM tools.
In [[object-oriented programming]], [[data management|data-management]] tasks act on [[object (computer science)|object]]s that are almost always non-[[scalar (computing)|scalar]] values. For example, consider an address book entry that represents a single person along with zero or more phone numbers and zero or more addresses. This could be modeled in an object-oriented implementation by a "Person [[Object (computer science)|object]]" with an [[attribute (computing)|attribute/field]] to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a list of addresses. The list of phone numbers would itself contain "PhoneNumber objects" and so on. Each such address-book entry is treated as a single object by the programming language (it can be referenced by a single variable containing a pointer to the object, for instance). Various [[Method (computer programming)|methods]] can be associated with the object, such as methods to return the preferred phone number, the home address, and so on.
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