Feature generation for note classification
In our experiments, features are divided into three main groups: input feature, local feature and global feature. Input features indicate the words or punctuation in note string. Local features are the characteristics of input features as in CRF models. We take the same 11 features used in our CRF learning for corpus level 1. Finally we generate a special type of features, global feature, which describes the distributional patterns of local features in a note string. For example, a global feature ‘NONUMBERS’ expresses the character of a note having no numbers in the string.
Five global features that seem useful for the separation are created.
- NOPUNC : there are no punctuation marks in the note
- ONEPUNC : there is just one punctuation mark in the note
- NONUMBERS : there are no numbers in the note
- NOINITIAL : the note includes no initial expressions
- STARTINITIAL : the note starts with an initial expression
Note that the typical features in text classification are the input features or their variations via dimension reduction techniques. Moreover, in most cases, the punctuation marks are not counted. However in our experiments, we actively test many possible features that can influence on the judgment over notes as bibliographic reference.
We show the experimental results of 10 important feature generation strategies. The baseline strategy is the first one that extracts only input words excluding punctuation marks. On each strategy, we commonly eliminate the numeric tokens and the unique tokens, which appear only one time in the corpus total. For the comparison, we take an example of note and describe the features generated by each strategy.
Example: M. Tozy et M. Mahdi, « Aspects du droit communautaire dans l’Atlas marocain », Droit et Société, 1990, p. 219-227.
|Input features||M. et M. Aspects du droit dans marocain Droit et Société p. , « », , , .|
|Local features||ALLCAP INITIAL FIRSTCAP ALLSMALL ALLCAP INITIAL FIRSTCAP PUNC PUNC FIRSTCAP ALLSMALL ALLSMALL ALLSMALL ALLSMALL NONIMPCAP ALLSMALL PUNC PUNC ITALIC FIRSTCAP ITALIC ALLSMALL ITALIC FIRSTCAP PUNC ALLNUMBERS PUNC ALLSMALL NUMBERS DASH PUNC|