Hermit Crab: Pictures
These are some pictures of the LinguaLinks user interface to Hermit Crab.
We start with a phonological rule. This picture shows the rule as it would appear in a pre-autosegmental phonology book, with each of the features in the rule's structural description and structural change shown. Notice that the features of the output take on the values of the corresponding features of the right-hand environment, as shown by the alpha variable notation. In other words, this rule assimilates the point of articulation of a nasal consonant to the point of articulation of a following stop.
It is possible to view this same rule in a somewhat simpler fashion, in which the individual features are replaced by a 'natural class' which abbreviates those feature values. That is, the user has defined the natural class 'nasal cons' to be the features [+consonantal +sonorant +nasal] (one might argue that the feature [+sonorant], and perhaps the feature [+consonantal], are redundant, but that is a different issue). Similarly, the user has defined a natural class 'stop', with the features [-nasal -continuant]. Finally, the user has defined another entitity, called 'consonant place', which is a variable including the features [anterior, back, coronal, high]. These variables function something like class nodes in autosegmental phonology, in that when they are used with the alpha notation, they imply that the features they include must be identical. In this example, since one of the two instances of this variable appears in the rule's output, the features of the other instance of that variable are copied (not spread) to the output.
It is important to realize that the above two views represent the same underlying object, i.e. they are notational variants.
The next picture shows a morphological rule, in this case for an affix of reduplication (which happens to mark the durative aspect). The morphological rule is embedded inside a 'sense' in a lexical entry of the LinguaLinks dictionary. As it says under the 'remarks' in the picture, the rule parses the base (stem) into the consitutents X[CV][CV] (numbered 1, 2 and 3), where C and V are natural classes of Consonants and Vowels, and X is a variable (whatever is left over, if anything). The result of applying the rule is to reduplicate constituent 2, i.e. the left-hand CV.
The final picture shows a portion of the derivation of a word, in which another morphological rule has applied to prefix maN- onto the stem pili. The 'N' is a nasal consonant of undefined point of articulation, so that immediately after the attachment of this affix, the word's phonological form is ambiguous: it could be mampili, manpili, or mangpili. The ambiguity is displayed for the user as a regular expression, ma[m n ng]pili, where the small brackets delineate the ambiguity. (Internally, Hermit Crab uses phonetic feature matrices, not letters; the letters are produced solely for the user's edification during debugging.) The ambiguity is removed by the application of the rule which assimilates a nasal to the point of articulation of a following stop (shown above), giving mampili. Finally, another phonological rule applies to delete the stop, giving mamili (and rendering the nasal assimilation process opaque).
These pictures and others are shown in an article describing Hermit Crab, which appeared in SIL's Notes on Linguistics volume 2, number 1.