Digital humanities


Maintained by: David J. Birnbaum (djbpitt@gmail.com) [Creative Commons BY-NC-SA 3.0 Unported License] Last modified: 2022-02-24T22:34:43+0000


XPath assignment #4

You can find an XML (TEI) version of Shakespeare’s Hamlet at http://dh.obdurodon.org/bad-hamlet.xml. We’ve deliberately damaged some of the markup in this edition to introduce some inconsistencies, but the file is well-formed XML, which means that you can use XPath to explore it. You should download this file to your computer (typically that means right-clicking on the link and selecting save as) and open it in <oXygen/>.

Prepare your answers to the following questions in a markdown file upload it to Canvas as an attachment. As always, code snippets (including XPath snippets) in markdown must be surrounded with backticks.

Some of these tasks are thought-provoking, and even difficult. If you get stuck, do the best you can, and if you can’t get a working answer, give the answers you tried and explain where they failed to get the results you wanted. As always, you are encouraged to ask questions in the #xpath channel in Slack, but because you want to make progress in learning to debug your own code, your questions should tell us what you tried, what you expected, exactly what you got instead (not just didn’t work or got an error), and what you think the source of the problem is. Sometimes writing that sort of request for advice that will help you figure out what’s wrong on your own (see Rubber duck debugging), and even when it doesn’t, it will help us identify the difficult moments.

These tasks require the use of path expressions, predicates, and functions. References to Kay are to the Michael Kay book; there’s a link in our online course description to a PDF version accessible through the Pitt library system. There may be more than one possible answer.

Using the Bad Hamlet document and the XPath browser window in <oXygen/>, construct XPath expressions that will do the following (give the full XPath expressions in your answers, and not just the results):

  1. What XPath will return a hyphen-separated list of all characters without duplicates. The resulting list will look something like:

    Claudius-Hamlet-Polonius ...

    Our solution uses string-join() (alternative solutions may also require distinct-values()). Note that there are several ways to identify the characters in this markup, including the <castList> element, the <speaker> elements, and the @who atribute on the <sp> element. Which should you use and why?

  2. Most metrical lines (<l>) have an @xml:id attribute with a value like sha-ham101010, ending in a six-digit number. The first digit is the act, the next two the scene, and the last three the line in the scene. Some metrical lines are split across multiple speakers, and in that case the six-digit number in the @xml:id value is followed by I (initial part), M (middle part), or F (final part). In a few places there may be more than one middle part, and in those cases the M is followed by a one-digit number. For example, one of Hamlet’s lines is:

    <l xml:id="sha-ham502277M2" n="277">One.</l>

    which is the second middle part. What XPath will return the number of <l> elements that are middle parts? Our solution uses count() and contains().

  3. Sometimes Rosencrantz speaks by himself and sometimes he speaks in unison with Guildenstern. What XPath finds all of the speeches by Rosencrantz, whether alone or together with Guildenstern? Our solution uses a single instance of contains().

  4. The string-length() function can be used in two ways. You can wrap it around an argument, so that, for example, string-length('Hi, Mom!') will return 8, the length in character count of the string inside the quotation marks. It can also be used as part of a path expression, so that, for example, if the XPath //sp returns a sequence of all <sp> elements, //sp/string-length(.) returns a sequence of the lengths of all <sp> elements as measured by counting characters. This works by finding all of the <sp> elements and then (next path step) getting the string length of each one. Remember that the dot inside the parentheses refers to the current context node, which is the member of the sequence of <sp> nodes that is being processed at the moment. We need to use this subterfuge because string-length(//sp) generates an error. The problem is that string-length() can take only a single argument, and //sp returns more than one item. Putting the string-length() function on its own path step with a dot inside means that it applies once for every <sp> element, and that each time it applies, it has just a single argument.

    In Real Life we are more likely to use the simple map operator (!) than a path step to apply a function to a sequence of nodes. That is, we would write //sp ! string-length(.) instead of //sp/string-length(.). The meaning is the same and both versions are correct, idiomatic XPath, but we prefer the simple map operator in this situation because it helps us recognize quickly that we’re applying a function, and not just selecting nodes.

    Use the information above to write an XPath expression that finds the length of the longest speech. What length does it return? Our solution uses string-length() and max().

  5. Optional, challenging question: Given the preceding solution, how can you use that XPath to retrieve the longest <sp> itself? No fair checking the length and then writing a separate XPath that looks for that number. Your answer must find the longest speech without your knowing how long it is. Our solution doesn’t require any additional functions beyond the ones used in #4, but it does use a complicated predicate.

  6. Optional, very challenging question: What XPath produces a numbered list of all characters, without any duplicates, which should look something like:

    1. Claudius

    2. Hamlet

    3. Polonius

    4. ...

    There are several possible solutions, each of which raises issues that you may not have seen before. If you get an error message, try to figure out what it means and how to resolve it.

What to submit

You should turn in your answers to the above questions in a markdown file, that is, a file with the extension .md.