A unification grammar defines the transfer relation between logical forms of two languages. Like in generation, the `input attribute' is a logical form. Instead of strings, logical forms of the target language are generated. For example the input to transfer may be a feature structure such as:
The bilingual grammar will apply its rules, testing after each application whether the value of the attribute subsumes the input feature structure. The value of the attribute will gradually be instantiated. At the end of the process, the system will test whether the input feature structure subsumes the value of the attribute . If this is the case, then the value of will be considered the output of transfer. An example of a simple rule in PATR notation is given as:
The integers are names of feature structures, where is used to represent the mother node and represent the daughter nodes. Application of this rule to the feature structure results in the following instantiation, where framed integers represent reentrancies. Transfer then continues by instantiating the feature structures 1, 2 and 3. The Dutch logical form is thus gradually instantiated as transfer proceeds by decomposing the English logical form:
An example of the rule for the first daughter will be a `lexical entry' and may look as in:
The complex English expression `prime minister' has to be translated as a simple expression in Dutch: `premier'. This rule can be defined as:
where it is assumed that the construction is analysed in English as an ordinary noun-adjective construction, and where the logical form of the adjective takes the logical form of the noun as its argument. Note that this example of complex transfer is similar to the famous `schimmel - white horse' case. As a result of the rule applications the value of the attribute will get instantiated resulting in:
from which the generator generates the string `De militairen hebben het vuur niet geopend op de Nederlandse premier'.