--- title: Eboard 17 Processing XML number: 17 section: eboards held: 2019-03-04 link: true --- CSC 151.02 2019S, Class 17: Processing XML ======================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * XML, revisited * Representing XML in Racket * Expressing patterns in XML * Constructing new documents from old * Lab Preliminaries ------------- ### News / Etc. * Mentor sessions Wednesday 8-9 p.m., Thursday 8-9 p.m., Sunday 5-6 p.m. * Welcome to any prospective students we have. Thank you for bringing warmer weather with you. * I'm back! We hope that you had a good time without us. * I brought you conference swag. (One of each item per person.) ### Upcoming work * Reading for Wednesday * [Forthcoming] * [Assignment 6](../assignments/assignment06) due Tuesday. * Quiz Friday: Hash tables, structs, and searching XML ### Extra Credit _I would certainly appreciate suggestions of other extra credit activities (preferably via email)._ #### Extra credit (Academic/Artistic) * Grinnell Singers, Sunday at 2pm. with Lyra Baroque Orchestra (professional musicians, period instruments), really difficult pieces by Handel and others. * Twelfth Night this weekend #### Extra credit (Peer) #### Extra credit (Wellness) #### Extra credit (Wellness, Regular) * 30 Minutes of Mindfulness at SHACS every Monday 4:15-4:45 * Any organized exercise. (See previous eboards for a list.) * 60 minutes of some solitary self-care activities that are unrelated to academics or work. Your email reflection must explain how the activity contributed to your wellness. * 60 minutes of some shared self-care activity with friends. Your email reflection must explain how the activity contributed to your wellness. #### Extra credit (Misc) ### Other good things ### Questions _Can we do overkill on the date time stuff, say paying attention to Julian/Gregorian switch?_ > You need not pay attention to the switch. But if it floats your boat, as they say, it's fine. _Can we talk about 1a?_ > Goal on 1a is to build a hash table that tallies letters, extract info in a systematic way. * Create a hash table. * Turn the string into a list of characters. * Iterate through the list, using for-each. If a character is a letter, count it in the hash table. If not, don’t. * Use the hash table to make a list of character/count lists. Here's an incomplete solution. ```drracket (define tally-letters (lambda (str) (let ([uh (make-hash)]) ; Initialize (for-each (section hash-set! uh <> 0) (string-split "abcdefghijklmnopqrstuvwxyz" "")) ; Fill in values (for-each (lambda (thing) (when (regexp-match? #px"[a-z]" thing) (hash-set! uh thing (+ 1 (hash-ref uh thing))))) (string-split str "")) uh))) ``` See exercise 7 on the hash tables lab for more ideas. XML, revisited -------------- * A mechanism for marking up documents using tags. There are tags like `

` for opening paragraphs and `

` for closing paragraphs. * The following is HTML * `` marks universal headings? * `` ... `` marks emphasized text. * `` ... `` marks quotation. * `` ... `` marks strongly emphasized text. * `` - list (unnumbered list) * `
    ` ... `
` - list (ordered list) * `
  • ` ... `
    • ` - list items * Reminder: `

    ` gives additional information about an element of the document. * Hierarchical. We can write programs that transform and analyze text. (Not a surprise at this time.) We should also be able to write programs that transform and analyze Web pages. _Write a regular expression that matches emphasized pieces of text so that we can count the number of emphasized pieces._ ```drrackeet > (regexp-match* #px"" example) '("" "" "" "" "") > (length (regexp-match* #px"" example)) 5 > (regexp-match* #px"Alice in CSC151land") '(" (regexp-match* #px"]" "Alice in CSC151land") '(" (regexp-match* #px"" "Alice in CSC151land") '("") > (length (regexp-match* #px"" example)) 5 ``` _Write a regular expression that matches *nested* emphasized pieces of text so that we can, say, replace the inner one with a tag. `Sam thinks this is very important!`_ Because XML/HTML are hierarchical and regular expressions are linear, regular expressions do poorly this kind of problem. There is no common pattern language for hierarchical structures. However, there is a standard for XML documents, called XPath. We will consider a subset of XPath. Representing XML in Racket -------------------------- XML is hierarchical, strings are not. How might we represent a hierarchical document in Racket? Options: Lists, Strings, Hash tables We can think about each HTML element as a list. For example `

    Hello world

    ` might be represented as `'(p "Hello world")`. `

    This is more complicated

    ` as `(p "This is " (em "more") " complicated")` `file->html` and `string->html` convert to this format `html->file` and `html->string` convert from this format Expressing patterns in XML -------------------------- `"//em"` - Search for this tag Constructing new documents from old ----------------------------------- Lab ---