LING/C SC/PSYC 438/538

1. LING/C SC/PSYC 438/538 Lecture 3 9/3 Sandiway Fong

2. Today’s Topics • Short Homework 1 • graded • Text summarization • a bit more on the extra-credit homework … • Perl Day continues! • Scalars last time…

3. Homework 1 Discussion • Flying saucer: idiom? anything disk-shaped will qualify UFO saucer

4. Homework 1 Discussion • Structural ambiguity: • I prodded the boy with a pole • [NP the boy] • [VP prodded[NP the boy]] • [PP with a pole]] http://www.merriam-webster.com

5. Homework 1 Discussion • Structural ambiguity: • I prodded the boy with a pole • [NP the boy] • [VP prodded[NP the boy]] • Phrase structure: adjunction, PP adjoins to … • [NP [NP the boy] [PP with a pole]] • [VP [VP prodded[NP the boy]] [PP with a pole]] • [PP with a pole]]

6. Homework 1 Discussion • Referential ambiguity: • John disliked nearly everyone that he knew pronoun coreferential with… not John but with someone else not mentioned in this sentence

7. Open Text Summarizer • Web interface • http://www.splitbrain.org/services/ots • (thanks! Paul Mithun)

8. Open Text Summarizer • From CNN this morning

9. Open Text Summarizer • From CNN this morning

10. Open Text Summarizer • From CNN this morning

11. Open Text Summarizer • From CNN this morning

12. Application of the Day • (Optional) Extra Credit for the Curious • (Deadlineextended to anytime before Thursday September 5th) • Discuss whether you think the summarizer does a good job. • Is the article one that’s easy to summarize? • Read up on summarization in J&M (23.3-23.4, pg787-795) • How do you think it works? • Do you think it should work on foreign language text? • Try it…

13. Perl Day • Learn Perl • Books… • Online resources • http://learn.perl.org/ • we begin with ... • http://perldoc.perl.org/perlintro.html • philosophy: Natural Language Principles in Perl • If a language is designed so that you can ``learn as you go'', then the expectation is that everyone is learning, and that's okay. • http://www.wall.org/~larry/natural.html

14. Useful notes • Notes from the tutorial: • whitespace not always necessary, e.g. • print"Hello class!\n”; • is fine, but good idea to consistently use spacing (not just for readability) • variable names must not begin with a number (use a letter), so • $538students is out • $students538 is ok • error messages frequently completely uninformative (and sometimes misleading), e.g. Bareword found where operator expected at example.prl line 3, near "$538students" (Missing operator before students?) • so make sure you write code consistently. • semicolon (;) is not always necessary • Command separator token semantics vs. end of command (termination) token • Best practice is to terminate every command with a semicolon

15. Perl arrays and hashes • Scalars: • strings, numbers (integers, floating point numbers), references • Arrays: • Store multiple scalars together • Idea: list of scalars • Access by index: 0,1,2,… • Hash: • Like an array except access not through a numeric index • Use user-specified keys $variable @variable %variable different namespaces: $apple @apple %apple are different data structures and can co-exist simultaneously

16. Perl Week

17. Perl Week

18. Perl Week • Notes on arrays and hashes • arrays are indexed from 0,1,2,3… • hashes are like arrays with user-defined indexing (aka associative array or hash table) • initialization (use round brackets and commas) • @a = (“zero”, “one”, “two”, “three”, “four”); • %h = (“zero”, 0, “one”, 1, “two”, 2, “three”, 3, “four”, 4); (key/value pairs) • access to individual elements (square brackets vs. curly braces) • $a[1] “one” • $h{zero} 0

19. Perl Week • Notes on arrays and hashes • output • print @a zeroonetwothreefour • print “@a” zero one two three four • print %h three3one1zero0two2four4 (note: different order) • print “%h” %h (literal, no interpolation) What happens here? • %pos = ("apple", "n", "speak", "v", "happy", "a", "walk", "n", "walk", "v"); • print $pos{"walk"}, "\n"; controlled by variable $” default: a space • (hash keys are unique)

20. Perl Week • Conditionals • if ( @a < 10 ) { print “Small array\n” } else {print “Big array\n” } • Note: @a here is a scalar = size of array • unless (@a > 10) { print “@a\n” } • Note: if size of array a is ≤ 10, it prints the contents of array a • Looping • %fruits = ("apple", "green", "orange", "orange", "lemon", "yellow"); • foreach $fruit (keys %fruits) { print $fruit, " => ", $fruits{$fruit}, "\n” } gives output: • lemon => yellow • apple => green • orange => orange • Note: apparently • keys %fruits = (“lemon” “apple” “orange”) is an array