Conference DSL queries

Write five EOL queries (Q1-Q5) that print:

• Q1: The number of days the conference lasts
• Q2: A set of unique affiliations of participants of the conference
  • i.e. if multiple persons have the same affiliation, the affiliation should appear only once in this set
• Q3: The total duration of all talks in the conference
• Q4: A set of all the names of the rooms in which breaks take place
• Q5: The number of tracks that start before noon
  • Reminder: Slot.start and Slot.end are strings that use the HH:MM format (e.g. 15:30).

Instructions for running your EOL queries against a conference model are provided below.

Solutions

// Q1
// Day.all returns a collection
// with all the instances of
// Day in our model
Day.all.size().println();

// Q2
// Collect the affiliations of
// all persons, and then filter
// out duplicates using asSet()
Person.all.collect(p|p.affiliation).asSet().println();

// Q2
// More verbose version that uses
// a for loop instead of .collect()
// You should avoid writing such code
var affiliations : Set;
for (p in Person.all) {
    affiliations.add(p.affiliation);
}
affiliations.println();

// Q3
// Get a list with the durations
// of all talks and compute their
// sum
Talk.all.collect(t|t.duration).sum().println();

// ... or more concisely
Talk.all.duration.sum().println();

// Q4
// Collect the rooms of all
// breaks and then collect
// the names of these rooms
Break.all.collect(b|b.room).asSet().collect(r|r.name).println();

// ... or more concisely
Break.all.room.asSet().name.println();

For Q5, we will need to define a few helper operations for working with HH:MM-formatted times first. For now, we assume that string values under Slot.start and Slot.end conform to the HH:MM format. Later on, we will encode (and check) this assumption using a validation constraint.

import "common.eol";

// Q5
// Select all tracks that start before noon
// and compute the size of the returned collection
Track.all.select(t|t.start.isBefore("12:00")).size().println();

Warning

The EOL execution engine ignores any statements that appear after the definition of the first operation in a .eol file. Therefore, if you were to move the first statement in the example above (Track.all.select(t|t.start.isBefore("12:00")).size().println();) to the end of the file, it would not get executed.

Running queries Q1-Q5

• To run these queries you will need
  • The Ecore metamodel of the Conference DSL;
  • A sample model that conforms to it;
  • An EOL file that contains your queries.
• You should already have conference.ecore (Ecore metamodel) and conference.model (sample model) in your workspace after following the instructions at the start of this practical.
• Create an empty text file named conference-queries.eol within your conference-dsl project.
• Right-click on conference.ecore.

• Click on the Register EPackages menu item. This will register the metamodel with EMF so that it can load models (such as conference.model) that conform to this metamodel.

• Open your conference-queries.eol file and type/paste your queries in it.

• Create a new EOL Program run configuration to run your EOL queries.

• Double-check that the path of your EOL file appears in the Source field of the Source tab of the run configuration dialog.

• Add the Conference model (conference.model) to the run configuration through the Models tab of the dialog.

• Set the name of the model to M

• Select conference.model as the model file. If the file selection dialog is empty, start typing the name of the file or ** to display all workspace files.

Warning

Double-check that you have selected the model file (conference.model) and not the metamodel file (conference.ecore) in this step. This is a common mistake to make.

• As soon as you select conference.model, the URI of its metamodel (conference) should be added to the Metamodels list of the dialog. If it doesn’t, it means that you have either not selected the correct model file, or that you have not registered your metamodel (conference.ecore) with EMF (see earlier steps).

• Click the Run button.

• The output of your queries should appear in the Console view.