Differential object marking

Differential object marking (DOM) is a linguistic phenomenon that is present in more than 300 languages; the term was coined by Georg Bossong. It is a form of differential argument marking that applies to the direct object.
Overview.
In languages where DOM is active, direct objects are divided in two different classes, depending on different meanings, and, in most DOM languages, only one of the classes receives a marker, the other being unmarked (but there are languages, like Finnish, where both types of objects are marked with different endings). Direct objects that are higher in "prominence" are more likely to be overtly case-marked.
The "prominence" is evaluated in the following ways:
These scales are also reflected in Silverstein’s person/animacy hierarchy.
Examples.
Spanish.
A well-known DOM language is Spanish. In Spanish, direct objects that are both human and specific require a special marker (the preposition "a" "to"):
Inanimate direct objects do not usually allow this marker, even if they are specific:
Yet, some animate objects that are specific can optionally bear the marker:
Some dialectal variation has been attested regarding the use of DOM in different varieties of Spanish. Balasch finds that, while the linguistic factors conditioning the use of DOM remain the same in both Mérida (Venezuela) Spanish and Madrid Spanish, DOM appears much more often in Madrid data. Furthermore, Tippets and Schwenter find that a factor known as "relative animacy" (the animacy of the direct object relative to that of the subject) is quite important in the implementation of DOM in varieties of Spanish such as Buenos Aires and Madrid Spanish. 
Sakha.
In languages like Turkish, Kazakh language and Sakha, more "prominent" objects take an overt accusative marker while nonspecific ones do not. Lack of an overt case marker can restrict an object's distribution in the sentence. Those orders are permitted in Sakha if accusative case is overtly expressed:
Sakha
However, when the object is nonspecific, alternative ordering is not permitted:
Sakha
When the direct object is low on the definiteness scale, it must directly precede the verb, whereas alternative ordering is possible when the direct object is higher in prominence.
Other languages.
Other examples of languages with differential object marking are Persian, Turkish, Copala Triqui, Khasi, Tamil, Malayalam, Kham, Hebrew and Amharic. A number of languages in Mozambique also show differential object marking.
In Turkish, the direct object can either have accusative case or have no (visible) case at all; when it has accusative case, it is interpreted as specific (e.g. one specific person), and otherwise it is interpreted as nonspecific (e.g. some person).
Differential Object Marking is not only found in spoken languages, but also in sign languages. In German Sign Language, for example, animate direct objects receive an additional marker while inanimate direct objects do not.
This is different from what happens in non-DOM languages, where all direct objects are uniformly marked in the same way; for instance, a language could mark all direct objects with an accusative ending (as in Quechua); other language could leave all direct objects without overt marker (as in English).
Bibliography.
Although the phenomenon has been known for a very long time, it was considered a minor quirk in a few languages until Georg Bossong, during the 1980s, presented evidence of DOM in more than 300 languages. Since then, it has become an important topic of research in grammatical theory. This is a selection of works that deal with the phenomenon: