Editing Tree-adjoining grammar (section)

==History==
TAG originated in investigations by Joshi and his students into the family of adjunction grammars (AG),<ref name="JoshiKosarajuYamada1969">{{cite document
 | last = Joshi
 | first = Aravind
 |author2=S. R. Kosaraju
 |author3=H. Yamada
 | title = String Adjunct Grammars
 | year = 1969
 | publisher = Proceedings Tenth Annual Symposium on Automata Theory, Waterloo, Canada }}
{{Citation
 | last1 =Joshi
 | first1 =Aravind K.
 | last2 =Kosaraju
 | first2 =S. Rao
 | last3 =Yamada
 | first3 =H. M.
 | title =String Adjunct Grammars: I. Local and Distributed Adjunction
 | journal =Information and Control
 | volume =21
 | issue =2
 | pages =93–116
 | year =1972
 | doi =10.1016/S0019-9958(72)90051-4
 | doi-access =free
 }}
{{Citation
 | last1 =Joshi
 | first1 =Aravind K.
 | last2 =Kosaraju
 | first2 =S. Rao
 | last3 =Yamada
 | first3 =H. M.
 | title =String Adjunct Grammars: II. Equational Representation, Null Symbols, and Linguistic Relevance
 | journal =Information and Control
 | volume =21
 | issue =3
 | pages =235–260
 | year =1972
 | doi =10.1016/S0019-9958(72)80005-6
 | doi-access =free
 }}
</ref> 
the "string grammar" of [[Zellig Harris]].<ref>{{cite book
 | last =Harris
 | first =Zellig S.
 | title =String analysis of sentence structure
 | publisher =Mouton & Co.
 | series =Papers on Formal Linguistics
 | volume =1
 | date =1962
 | location =The Hague
 }}</ref> AGs handle [[exocentric]] properties of language in a natural and effective way, but do not have a good characterization of [[endocentric]] constructions; the converse is true of [[rewrite rule|rewrite grammars]], or [[phrase-structure grammar]] (PSG). In 1969, Joshi introduced a family of grammars that exploits this complementarity by mixing the two types of rules. A few very simple rewrite rules suffice to generate the vocabulary of strings for adjunction rules. This family is distinct from the [[Chomsky hierarchy|Chomsky-Schützenberger hierarchy]] but intersects it in interesting and linguistically relevant ways.<ref name="Joshi1969">{{cite document
 | last = Joshi
 | first = Aravind
 | title = Properties of Formal Grammars with Mixed Types of Rules and Their Linguistic Relevance
 | year = 1969
 | publisher = Proceedings Third International Symposium on Computational Linguistics, Stockholm, Sweden }}</ref> The center strings and adjunct strings can also be generated by a [[dependency grammar]], avoiding the limitations of rewrite systems entirely.<ref name="joshi-rambow2003">{{cite conference
 | last = Joshi
 | first = Aravind
 |author2=Owen Rambow
  | title = A Formalism for Dependency Grammar Based on Tree Adjoining Grammar
 | year = 2003
 | book-title = Proceedings of the Conference on Meaning-Text Theory
 | url = http://www1.cs.columbia.edu/~rambow/papers/joshi-rambow-2003.pdf}}</ref>
<ref name="xtagenglish">{{cite web
  | title = A Lexicalized Tree Adjoining Grammar for English
 | url = http://www.cis.upenn.edu/~xtag/tech-report/}}</ref>