Add a sample UML diagram and model descriptions to ical-tasks

[ronaldtse]

Originally ported from:

• Add a sample UML diagram and model descriptions to ical-tasks PUBLIC_DRAFTS#29

For @douglm .

This PR adds the following to the iCal-Tasks document:

• A UML diagram
• Two UML classes, a "Calendar" and an "Event". It would be easy to rename them into "VCalendar" and "VTodo" and add the appropriate attributes, etc.

The UML syntax used is called LutaML:

• https://github.com/lutaml/lutaml-uml/blob/main/LUTAML.adoc

Structure

The diagram is stored at:

• ical-tasks/sources/views/calendar_view.lutaml

The class definitions are at:

• ical-tasks/sources/model/calendar.lutaml
• ical-tasks/sources/model/event.lutaml

The LutaML structure works like this:

• A diagram is needed to wrap any classes
• A diagram can include many classes
• A class can be "associated" with another class via UML relationships such as "generalization", "association", etc (see syntax)

Rendering in text

In the new file sections/70-model.adoc, it looks like this:

== Model
=== General

lutaml_diagram::views/calendar_view.lutaml[]

// Calendar
[lutaml_uml_class,views/calendar_view.lutaml,Calendar]

// Event
[lutaml_uml_class,views/calendar_view.lutaml,Event]

== Class attribute tables

[lutaml_uml_attributes_table,views/calendar_view.lutaml,Calendar]

[lutaml_uml_attributes_table,views/calendar_view.lutaml,Event]

lutaml_diagram

This line: lutaml_diagram::views/calendar_view.lutaml[]

Makes Metanorma render the diagram.

lutaml_uml_class

This line: [lutaml_uml_class,views/calendar_view.lutaml,Calendar]

Makes Metanorma render a clause that contains the descriptions and definitions of the UML class "Calendar" class.

lutaml_uml_attributes_table

This line: [lutaml_uml_attributes_table,views/calendar_view.lutaml,Calendar]

Makes Metanorma render a table of UML attributes for the "Calendar" class in the calendar_view.lutaml view.

That's it

Hope this helps!