Project: Housing Cooperative (german: Wohnungsgenossenschaft)

All exercises are based on a common “project”: the database of a housing cooperative that owns houses with rental apartments in cities all over Germany.

1. Assume that cities are uniquely identified by their name. Also, every street name exists at most once in every city.
2. For each building that is owned by the cooperative, the address (city, street, house number) is stored. It is also stored how many apartments are in the building (assume that always all apartments in the building are owned by the cooperative).
   • The building Hauptstraße 100 in Göttingen consists of 80 apartments.
   • The building Rheinstraße 53 in Köln consists of 100 apartments.
3. Every apartment has a (unique) number in its building. For each apartment, the number of rooms, the size (in square meters) and the current monthly rent (=Kaltmiete) is stored.
   • The apartment with the number 42 of the building Hauptstraße 100 in Göttingen has three rooms, 82 m², for 850 EUR per month.
   • The apartment with the number 43 of the same building has two rooms, 50 m², for 550 EUR per month.
   • The apartment with the number 17 of the building Rheinstraße 53 in Köln has three rooms, 95 m², for 1300 EUR per month.
4. For being entitled to rent an apartment in a cooperative, persons must buy a share and become members of the cooperative. For every person, the name, the (unique) membership code (recall that XML IDs must start with a letter), the birthdate, and the birth place (city name, country) are stored.
   • John Doe is born on February 28th, 1995 in Boston, USA.
   • Markus Meier is born on July 10th, 1980 in Göttingen, Germany.
   • Liese Müller is born on October 1st, 1950 in Köln, Germany.
   • Jan Jansen is born on August 10th, 1985 in Stockholm, Sweden.
5. For every individual rental agreement (=Mietvertrag) the name of the tenant (=Mieter) is stored (assume that the agreement is always made with a single person), together with the starting date, and the contact address where the tenant lived when the contract was signed.
   Contracts always begin with the first day of a month, and end with the last day of a month.
   Additionally, it is stored whether the contract is terminated or announced to be terminated, and for which date (=gekündigt; in Germany, a rental contract must be announced to be terminated three months in advance – e.g. today you could announce to terminate the contract for your apartment for November 30th, 2020).
   • John Doe lives in the apartment nr. 42 of the building Hauptstrasse 100 in Göttingen since April 1st, 2018. The contract is not announced to be terminated.
   • Markus Meier lives in the apartment nr. 43 of the building Hauptstrasse 100 in Göttingen since August 1st, 2011. He already announced to terminate the contract for October 31st, 2020.
   • Liese Müller lives in the apartment nr. 17 of the building Rheinstrasse 53 in Köln since March 1st, 1990. She announced to terminate the contract for August 31st, 2020.
6. When a new contract is signed, the (at this point current) address of the tenant and the starting date of the contract is stored.
   • The above-mentioned Markus Meier has signed a contract for the apartment nr. 17 of the building Rheinstrasse 53 in Köln, beginning October 1st, 2020.
   • Jan Jansen, who currently lives at the address Hafenstrasse 10, Hamburg (this apartment is not owned by the cooperative), signed a contract for the apartment nr. 43 of the building Hauptstrasse 100 in Göttingen from December 1st, 2020 on.
7. If a tenant moves somewhere else (not necessarily to an apartment of the cooperative), the new address is stored (e.g., to send the final cost bills).
   • The future address of Liese Müller is Mühlengasse 24, Mühlhausen in a building that does not belong to the cooperative.
8. Data about older contracts is kept in the database, it is not deleted.

And now ... the first Exercise:

Design an XML structure (use the frame given in file exam.xml) and fill it with some sample data (e.g. with some of the example data given in the text).
(Information about handling dates in XML can be found in the course’s slides around Slide 300.)

Copy-and-paste the XML from the file exam.xml afterwards (at the end of the exam, because it will be extended in later exercises) here:

Develop the DTD for your document developed in Exercise 1, use the file exam.dtd.
Use the saxon call

saxonValid.bat -s:exam.xml

for validating it.
Copy-and-paste the DTD from the file exam.dtd afterwards here:

Use your XML file exam.xml as a basis for solving this and the following exercises.
None of the results should contain duplicates.

Give an XPath query or an XQuery query that returns the names of all cities where the cooperative owns at least one apartment that consists of exactly three rooms.

Write the XPath query string in the file query1.xq and call it with

   saxonXQ.bat -s:exam.xml query1.xq

Copy-and-paste the query from query1.xq afterwards here:

Add additional sample data to your XML designed in Exercise 1 to test that your result does not return duplicates in case that there are multiple such apartments in a city.

Paste your result of evaluating the query from Exercise 3 (XPath (a)) here:

Give an XPath query or an XQuery query that returns the names of all persons who have currently rented an apartment that consists of exactly three rooms and costs less than 900 EUR.
(note: the current date can be obtained by the XPath function current-date().)

Copy-and-paste the query from query2.xq afterwards here:

Give an XPath query or an XQuery query which, for every city, yields the total earnings of the cooperative in October 2020. The results should be of the format

  <city name="..." total="..."/>

Copy-and-paste the query from query3.xq afterwards here:

Give an XPath query or an XQuery query that yields the names of all persons who ever rented an apartment of the cooperative, but never rented an apartment of the cooperative in Köln.

Copy-and-paste the query from query4.xq afterwards here:

Give an XQuery query or an XPath query that returns the names of all cities such that in every building owned by the cooperative in this city there is at least one apartment that has at least 100 square meters.

Copy-and-paste the query from query5.xq afterwards here:

Give an XQuery query that returns information about all persons who moved from one apartment directly to another (both owned by the cooperative), and the second apartment is more expensive than the one before (use the current rent for time-independent comparison of “expensiveness” of apartments).
The results should be of the format

  <person name="..." rent1="..." rent2="..."/>

Copy-and-paste the query from query6.xq afterwards here:

Give an XQuery query or an XSLT stylesheet that, for each city “A”, gives a list of all cities “B” such that some person moved directly from an apartment in city “A” to an apartment in “B”, and both of the apartments belong to the cooperative.
for each such city “A”, the result should be of the form

<result city="name-of-city-A">
 
name-of-city-B1 ... name-of-city-Bn
 </result>

(no duplicate B’s, in any order, with arbitrary whitespaces)

Copy-and-paste the query from query7.xq afterwards here:

Extend the given XSL stylesheet frame exam.xsl to an XSLT stylesheet that for each person returns the name in an h3-element, followed by an HTML list that chronologically lists all apartments (by address) that the person had rented from the cooperative.
(an HTML list consists of an ul-element with nested li-elements; omit the surrounding HTML stuff, don’t care too much for formatting)

Use the following call to execute it:

   saxonXSL.bat -s:exam.xml exam.xsl 

Copy-and-paste the XSLT stylesheet from exam.xsl afterwards here:

Describe (short and concisely) what ID and IDREF in XML, and primary keys and foreign keys in relational databases both are used for:

Describe two aspects in which the ID/IDREF mechanism in the XML world differs from the primary key/foreign key concept in relational databases: