Digital humanities

Maintained by: David J. Birnbaum ( [Creative Commons BY-NC-SA 3.0 Unported License] Last modified: 2016-11-16T13:44:36+0000

XQuery assignment #2

About FLWOR constructions

This assignment requires the use of a FLWOR construction, so you might want to review the assigned reading before tackling it. Be sure that you understand what each of the components of a FLWOR does, and how they interact. For example, you can get the title of every play in the corpus with a single XPath statement:

xquery version "3.0";
declare namespace tei="";

To get the same result with a FLWOR expression (alphabetizing the titles on the way), you might use:

xquery version "3.0";
declare namespace tei="";
let $plays := collection('/db/apps/shakespeare/data')
for $play in $plays
order by $play
return $play//tei:titleStmt/tei:title

We use the let statement to set a variable $plays equal to the collection of all 42 plays. We then use a for statement to iterate over the plays, doing something once for each play. Remember that the components of a FLWOR expression must occur in FLWOR (for, let, where, order by, return) order, except that you can have as many for and let statements as you want, and they can occur in any order with respect to one another. If there is a where statement, it must follow all of the for and let statements; if there is an order by statement, it must come next; and the return statement must come last. There must be at least one for or let statement and exactly one return statement; everything else is optional.

While we iterate over the plays with our for statement, we use an order by statement to sort them alphabetically, taking advantage of the fact that the first textual content of each play is the title, so alphabetizing by the entire text of the play is equivalent to alphabetizing by the title. Note that when we return the title of each play, the XPath in the return statement has to begin with the variable $play, so that on each of the 42 iterations we’ll be getting the title of the play we’re looking at at that moment.

The texts

Obdurodon contains the text of forty-two Shakespearean plays. In the TEI markup for these plays, speeches are <sp> elements and the speakers are <speaker> elements that are their first children. For example:

<sp who="Roderigo">
    <l xml:id="sha-oth101040F" n="40">I would not follow him then.</l>

There are 966 distinct speaker names (values of the <speaker> element) in the entire corpus, some of which show up in more than one play. Three of the names show up in more than ten plays: there is a character called Messenger in 22 plays, one called All in 20 plays, and one called Servant in 18. (These aren’t the same messenger or all or servant, of course!) Here are the details:


Your assignment is to write XQuery that will query the collection of plays, find the three <speaker> element values that occur in more than ten plays, and return a list of those elements along with the names of the plays in which they occur. That is, you should write XQuery that generates the basic information in the preceding list. Once your XQuery is working, copy it into a plain-text document (not a Word document), save it, and upload it to CourseWeb. You can create a plain-text (that is, .txt) document in <oXygen/> by creating a new document of type Text. We don’t need to see the output of your XQuery; all we need is the XQuery code itself.

Our list includes some enhancements that you can consider optional for this assignment, but if you get the basic solution, we hope you’ll try them:

Our solution used several let statements to configure convenience variables. We used distinct-values() and a for statement to find and iterate over all of the distinct <speaker> names in the collection. We used the count() function and a where statement to find all of the names of speakers that occur in more than ten plays. Finally, we used both concat() and string-join() in our return statement to glue the pieces together. For the optional parts, we used an order by statement to sort the results in descending order of frequency, and to alphabetize the play titles we used an embedded FLWOR statement. That means that we set a variable equal to the return of a FLWOR statement, which is a powerful way of using FLWOR not just for the main program flow, but also to control subcomponents. We used the XPath translate() function to fix the apostrophe.

This is not a difficult problem intellectually: you can paraphrase it easily as find all of the speaker names that show up in more than ten plays. It is, however, a complicated pattern to formalize, and because the XQuery version has to be explicit, it is longer than the prose formulation. We would suggest breaking the problem down into subcomponents like

Some of the preceding questions are easier than others, but getting all the way to a solution means getting them all correct and stitching them together effectively, which is why we recommend developing your XQuery step by step and testing it after every step, so that when it breaks, you’ll know which statement caused the problem. If you can’t get all the way to a solution, that’s okay, but you can’t just give up; what you need to do instead is submit your solutions to as many of the pieces as you can (both the ones we list above and any others that you recognize as important). While this particular assignment is a bit (okay, more than a bit) artificial, the techniques required are very common in Real Life: find information across documents and create a report based on an aggregated result.

Watch out for namespaces!

The plays are all in the TEI namespace. This means that you’ll want to declare a namespace prefix and map it to the TEI namespace, as you did in the last assignment. What tripped up several people in the last assignment, though, is that all element names in your XPath expressions require the namespace prefix. For example, if you’ve set the value of a variable $plays to the 42 play documents in the corpus and if you’ve also set the prefix tei: to point to the TEI namespace, you can get the titles of all of the plays with the XPath expression $plays//tei:titleStmt/tei:title. If you forget the prefix on either <titleStmt> or <title>, though, you won’t get any results because you’ll be looking for one or both of those elements in no namespace, and every element in this corpus is in the TEI namespace.