为什么我的chdir文件句柄在Perl中不起作用？(Why does my chdir to a filehandle not work in Perl?)

 他们可能会使用信息提取技术。 
 
 以下是斯坦福大学SUST工具的演示： 
 
 http://nlp.stanford.edu:8080/sutime/process 
 
 您将在文档中提取关于n-gram（连续词）的属性： 
 
 
 
 numberOfLetters 
 
 
 numberOfSymbols 
 
 
 长度 
 
 
 previousWord 
 
 
 nextWord 
 
 
 nextWordNumberOfSymbols 
 ... 
 
 
 然后使用分类算法，并提供正，负的例子： 
 
Observation  nLetters  nSymbols  length  prevWord  nextWord isPartOfDate  
"Feb."       3         1         4       "Wed"     "29th"   TRUE  
"DEC"        3         0         3       "company" "went"   FALSE  
...
 
 你可能会有50个例子，但越多越好。 然后，该算法基于这些示例学习，并且可以应用于以前未见过的未来示例。 
 
 它可能会学习诸如 
 
 
 
 如果以前的单词只是字符，也可能是... 
 
 
 现在的词是“二月”，“马尔”，“...” 
 
 
 下一个单词在“第十二”，any_number ... 
 
 
 那么是日期 
 
 
 这是Google工程师就此题材播放的体面视频 

They likely use Information Extraction techniques for this.
 
Here is a demo of Stanford's SUTime tool:
 
http://nlp.stanford.edu:8080/sutime/process
 
You would extract attributes about n-grams (consecutive words) in a document:
 
 
 
numberOfLetters
 
 
numberOfSymbols
 
 
length
 
 
previousWord
 
 
nextWord
 
 
nextWordNumberOfSymbols
 ...
 
 
And then use a classification algorithm, and feed it positive and negative examples:
 
Observation  nLetters  nSymbols  length  prevWord  nextWord isPartOfDate  
"Feb."       3         1         4       "Wed"     "29th"   TRUE  
"DEC"        3         0         3       "company" "went"   FALSE  
...
 
You might get away with 50 examples of each, but the more the merrier. Then, the algorithm learns based on those examples, and can apply to future examples that it hasn't seen before.
 
It might learn rules such as 
 
 
 
if previous word is only characters and maybe periods...
 
 
and current word is in "february", "mar.", "the" ...
 
 
and next word is in "twelfth", any_number ...
 
 
then is date
 
 
Here is a decent video by a Google engineer on the subject