Morpho logy , Morpho log ical Process es and Morpho log ical Process ing

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Morpho logy , Morpho log ical Process es and Morpho log ical Process ing. John Barnden School of Computer Science University of Birmingham Natur al Language Process ing 1 2010/11 Semester 2. Overview. - PowerPoint PPT Presentation

Transcript of Morpho logy , Morpho log ical Process es and Morpho log ical Process ing

  • Morphology,Morphological Processes andMorphological ProcessingJohn Barnden

    School of Computer ScienceUniversity of Birmingham

    Natural Language Processing 1 2010/11 Semester 2

  • OverviewMorphology is to do with the shape (internal structure) of words and how the shape changes to reflect certain common, fairly systematic changes of meaning. E.g.:forming plurals of many nouns by adding an s; but also irregular plurals (e.g. goose to geese); forming the past tense of many verbs by adding ed; going from buy to buyer; going from happy to unhappy; forming doghouse.Many such changes (not all) involve adjustments of substructure.Such substructure is a matter of decomposition into meaning-bearing/affecting subunits (as opposed, e.g., to individually meaningless letters or letter-strings).

  • Overview, contdMorphological processes are the ways, alluded to on the previous slide, in which words can, so to speak, change [more exactly: certain ways in which words are related to each other].Morphological processing is about how to computationally convert between words according to morphological processes, how to analyse words into their components if any, and how to create words from such components.Lectures will cover a start on this, with further detail left to the textbook.The basic tools are regular expressions or (equivalently) finite state automata.

  • MorphemesMorphemes are the components of words that we will be considering.They are variously described as (for any particular language):the minimal units of grammatical analysis the minimal units of meaningthe minimal units that bear meaning [J&M p.81]Possibly better : the minimal units that bear or affect meaning.

  • Examples of MorphemesConsider the word unhappiness:composed of three morphemes, each carrying a certain amount of meaning:un here means opposite of [or not in many other cases]ness means being in a state or conditionhappy: the familiar word (slightly modified by being combined on the right).One classification of morphemes:happy is a free morpheme because it can appear on its own and still mean the same as in the word above.un and ness are bound morphemes as they have to be attached to a free morpheme they cant mean what they do above when standing on their own. But:There is a completely unrelated word ness.There is a rather informal word un derived from the un morpheme, meaning something like unimportant, characterless, ineffectual, ... happy can act as part of a bigger word in other ways, as in trigger-happy.

  • Affixes Affixes are an important type of (usually bound) morpheme, usually small, and making a largely predictable meaning change thats largely independent of what they are applied to.In unhappiness, there are two kinds of affix:a prefix, una suffix, ness.There are also infixes in some languages (and perhaps, in special cases, in English). Bontoc [from the Philippines uses] infix um to change adjectives and nouns into verbs. So the word fikas, which means strong is transformed into fumikas meaning be strong.English: unhappy unbloodyhappy [slang] and similarly with some other favourite swear words.See textbook for circumfixes.

  • Affixes, contd Other examples of prefixes:re: conveys repetition or renewal, as in redevelop or retile or re-examinemis: conveys doing something wrongly, as in misrememberde and dis: convey removal, undoing or reversal, as in depopulate, disembowel, disappearin [or im before some consonants]: often conveys negation, as in indecisive, immeasurable, imperfectin [or im]: can also convey being/putting into a state, as in invigorate, inflammableanti: indicates opposition, as in antisemiticante: indicates beforeness [spatial or temporal], as in antenatalpre: indicates beforeness [spatial or temporal], as in prefix !

  • Affixes, contd Other examples of suffixes:ing: changes a verb infinitive into progressive form, as in buyings [changed to es after some consonants]: makes a noun plural or changes a verb infinitive into 3rd-person singulared [or d or t]: changes a verb infinitive into past tense or past participle formity: makes a noun out of an adjective, as in activity, purityless: indicates lack of something [could perhaps be considered a free morpheme because so close in meaning to the word less]ish: indicates likeness, closeness or somewhatness, as in bluish and city-ishI invented somewhatness by freeish application of morphology!

  • Cautions re Affixes, etc.Letters at beginning or end of a word can of course look like, but not be, a particular affix. Two examples:re is sometimes not the abovementioned prefix, as in regal, ready, regionly is sometimes not the adverb-creating suffix, as in holy, lily, hillyA word need not contain any free morpheme:E.g., inhere, cohere and adhere are all formed from a commonly prefixed bound morpheme plus the morpheme here the latter means to stick (from a Latin verb) but is not itself usable as a word of English with such a meaning.Affixes can be concatenated (strung together) to some extent :E.g. : morphologically, antidisestablishmentarianism, moralizingSome languages, e.g. Turkish, allow concatenation much more extensively (see textbook).

  • Cautions re Affixes, etc., contd.Affixes can adjust the meaning of what theyre affixed to in somewhat subtler ways than you might expect:E.g., entomb comes from en [meaning put in] and tomb, but it usually has a broad metaphorical meaning, and less usually means put in a [literal] tomb. Such formation of verbs from nouns often uses metaphorical meanings of the main morpheme rather than literal meanings.

  • Word StemsA word often has one intuitively-main morpheme:unhappiness: main morpheme is happyThe main morpheme is called the stem of the word, and may be the whole word.The stem is often a free morpheme, but need not be.Well see below that a word can contain more than one free morpheme, and in such cases the idea of a stem may be more difficult.

  • Types of Morphological ProcessIts convenient to divide morphological processes into four rough types:InflectionDerivationCliticizationCompoundingIts difficult to devise a precise definition of these types, even within a single language. Theres some overlap.

  • InflectionInflection is a morphological process that varies a word in certain very limited, standard, predictable ways, typically via affixes, keeping some large part of meaning intact,but changing the values of certain standard parameters. The variations are usually tightly related to the grammatical structure of the surrounding expression. Examples in English on next slide ...

  • Inflection: ExamplesNouns:Pluralizing a singular noun (a basic example: cat to cats)Forming possessive forms of a noun (a basic example: cats and cats )Pronouns and related adjectives: Setting the case/number (e.g., in varying between nominative I/we/who, accusative me/us/whom, possessive forms my/mine/our/ours/whose) . Also demonstrative pronouns and adjectives: this/these, that/those.Verbs:Setting the case, number, tense, etc. (infinitive eat to eats/ate/eaten; be to am/is/are/was/were)Forming the present participle by adding ing, used in progressive constructions (I am / was / will be buying) and as a gerund (a form of noun, as in the cutting of the cake).Adjectives and adverbs:Forming the comparative and superlative forms (e.g., big to bigger and biggest; fast [as adverb] to faster and fastest; and in colloquial English quickly to quicker and quickest).

  • Inflection, contd.Other languages may do things not done, or not done much, in English, e.g.:inflect nouns for case (nominative, accusative, etc.)inflect a definite article for case and number (whereas in English its always just the).Conversely, other languages do not do some things English does (e.g., Japanese nouns dont have plural or possessive forms).

  • Inflection, contd.Inflection often involves certain systematic spelling changes to the stem, e.g.Final c becomes ck as in picnic to picnickingDropping of a single, not separately pronounced e when adding ing (but dont drop when have ee)Doubling of final consonant when adding a suffix starting with e or i (as in beg to begging, and big to bigger).Inflection includes cases where meaning variations of the sorts on previous slide are reflected by irregular word forms (consider irregular verbs such as be, irregular plurals such as geese and mice). So inflection is not just about systematic lexical changes. (The textbook is slightly inconsistent on this.)Inflection includes the case where the word form is actually unchanged (e.g. hit : infinitive and past-tense form and past participle).

  • DerivationDerivation is a morphological process that varies a word in ways not covered by inflection, and less systematicbut still by means of relatively small changes in form such as adding affixes (or no change at all),usually involving a bigger shift of meaningthat is somewhat unpredictableExamples in English ....

  • Derivation: ExamplesMaking adjectives into adverbs by suffixing with ly.Making nouns (etc.) into adverbs by suffixing with wards, as in sidewards.Nominalizing (= nounifying) verbs by suffixing with ation or ment (as in payment), ee (as in payee), er (as in payer).Making nouns into verbs without changing the spelling (as in pencil, book, impact, carpet, bus, powerpoint). Verbifying nouns by suffixing with ify! Or with ise/ize.Nominalizing adjectives by suffixing with ness, ity.Making nouns into adjectives by suffixing with ish, y (as in frilly), [-]like, less, [e]d.Making verbs into adjectives by suffixing with able/ible.Other more ad hoc cases such as in iffy (from if), use of big as a verb (in big it up), ... Can you think of any other cases?

  • Unclear inf