### 13.1 Lexical entries ¶

Lexical entries consist of three basic parts, a head word, a part of speech and a pronunciation. The headword is what you might normally think of as a word e.g. ‘`walk`’, ‘`chairs`’ etc. but it might be any token.

The part-of-speech field currently consist of a simple atom (or nil if none is specified). Of course there are many part of speech tag sets and whatever you mark in your lexicon must be compatible with the subsystems that use that information. You can optionally set a part of speech tag mapping for each lexicon. The value should be a reverse assoc-list of the following form

    (lex.set.pos.map
       '((( punc fpunc) punc)
         (( nn nnp nns nnps ) n)))

All part of speech tags not appearing in the left hand side of a pos map are left unchanged.

The third field contains the actual pronunciation of the word. This is an arbitrary Lisp S-expression. In many of the lexicons distributed with Festival this entry has internal format, identifying syllable structure, stress markigns and of course the phones themselves. In some of our other lexicons we simply list the phones with stress marking on each vowel.

Some typical example entries are

    ( "walkers" n ((( w oo ) 1) (( k @ z ) 0)) )
    ( "present" v ((( p r e ) 0) (( z @ n t ) 1)) )
    ( "monument" n ((( m o ) 1) (( n y u ) 0) (( m @ n t ) 0)) )

Note you may have two entries with the same headword, but different part of speech fields allow differentiation. For example

    ( "lives" n ((( l ai v z ) 1)) )
    ( "lives" v ((( l i v z ) 1)) )

See Lookup process, for a description of how multiple entries with the same headword are used during lookup.

By current conventions, single syllable function words should have no stress marking, while single syllable content words should be stressed.

NOTE: the POS field may change in future to contain more complex formats. The same lexicon mechanism (but different lexicon) is used for holding part of speech tag distributions for the POS prediction module.