AhoIndexed:
  type: article
  title: Indexed Grammars—An Extension of Context-Free Grammars
  author: Aho, Alfred V.
  date: 1968-10
  page-range: 647-671
  url: https://doi.org/10.1145/321479.321488
  serial-number:
    doi: 10.1145/321479.321488
    issn: 0004-5411
  abstract: A new type of grammar for generating formal languages, called an indexed grammar, is presented. An indexed grammar is an extension of a context-free grammar, and the class of languages generated by indexed grammars has closure properties and decidability results similar to those for context-free languages. The class of languages generated by indexed grammars properly includes all context-free languages and is a proper subset of the class of context-sensitive languages. Several subclasses of indexed grammars generate interesting classes of languages.
  parent:
    type: periodical
    title: J. ACM
    publisher:
      name: Association for Computing Machinery
      location: New York, NY, USA
    issue: 4
    volume: 15