Difference between stem and lemma

lemma與stem的區別

Difference between stem and lemma

先從wikipedia上看看什麼是stem，什麼是lemma？

Lemma(morphology)：In morphology and lexicography, a lemma (plural lemmas or lemmata) is the canonical form, dictionary form, or citation form of a set of words(headword). In English, for example, run, runs, ran and running are forms of the same lexeme, with run as the lemma. Lexeme, in this context, refers to the set of all the forms that have the same meaning, and lemma refers to the particular form that is chosen by convention to represent the lexeme. In lexicography, this unit is usually also the citation form or headword by which it is indexed. Lemmas have special significance in highly inflected languages such as Turkish and Czech. The process of determining the lemma for a given word is called lemmatisation.

word stem：In linguistics, a stem is a part of a word. The term is used with slightly different meanings. In one usage, a stem is a form to which affixes can be attached. Thus, in this usage, the English word friendships contains the stem friend, to which the derivational suffix -ship is attached to form a new stem friendship, to which the inflectional suffix -s is attached. In a variant of this usage, the root of the word (in the example, friend) is not counted as a stem.In a slightly different usage, which is adopted in the remainder of this article, a word has a single stem, namely the part of the word that is common to all its inflected variants.Thus, in this usage, all derivational affixes are part of the stem. For example, the stem offriendships is friendship, to which the inflectional suffix -s is attached.

Difference between stem and lemma：

Stem is the part of the word that never changes even when morphologically inflected, whilst a lemma is the base form of the word. For example, from "produced", the lemma is "produce", but the stem is "produc-." This is because there are words such as production.In linguistic analysis, the stem is defined more generally as the analyzed base form from which all inflected forms can be formed. When phonology is taken into account, the definition of the unchangeable part of the word is not useful, as can be seen in the phonological forms of the words in the preceding example: "produced" /prəˈdjuːst/ vs. "production" /prəˈdʌkʃən/.Some lexemes have several stems but one lemma. For instance "to go" (the lemma) has the stems "go" and "went". (The past tense is based on a different verb, "to wend". The "-t" suffix may be considered as equivalent to "-ed".)

從上面咱們能夠看出，lemma通常是指詞型的還原，通常就是一個結果，而stem是詞幹，根據不一樣的定義略微不一樣，下面咱們看下使用程序分析的結果，其中lemma使用stanford的NLP工具，stem使用NLTK包中的stem（snow，porter，lancaster三個算法）

原句：This work shows that single and double Ala substitutions of His18 and Phe21 in IL-8 reduced up to 77-fold the binding affinity to IL-8 receptor subtypes A (CXCR1) and B (CXCR2) and to the Duffy antigen.

lemma：this work show that single and double alum substitution of his18 and phe21 in il-8 reduce up to 77-fold the binding affinity to il-8 receptor subtype a -lrb- cxcr1 -rrb- and b -lrb- cxcr2 -rrb- and to the duffy antigen .

snowstem：this work show that singl and doubl ala substitut of his18 and phe21 in il-8 reduc up to 77-fold the bind affin to il-8 receptor subtyp a ( cxcr1 ) and b ( cxcr2 ) and to the duffi antigen .

porterstem：Thi work show that singl and doubl Ala substitut of His18 and Phe21 in IL-8 reduc up to 77-fold the bind affin to IL-8 receptor subtyp A ( CXCR1 ) and B ( CXCR2 ) and to the Duffi antigen .

lancasterstem：this work show that singl and doubl ala substitut of his18 and phe21 in il-8 reduc up to 77-fold the bind affin to il-8 receptor subtyp a ( cxcr1 ) and b ( cxcr2 ) and to the duffi antigen .