Support graph traversal of linked iCalendar and vCard objects

This library makes use of relationships defined in iCalendar and vCard objects to construct a traversable, directed graph. For iCalendar objects these relationships are typically defined in RELATED-TO, LINK, and STRUCTURED-DATA properties. vCard relationships are typically defined by the MEMBER, RELATED, FBURL and CALURI properties.

The following properties are used to construct a graph edge from an iCalendar component to another object.

The RELATED-TO iCalendar property is supported in VEVENT, VTODO and VJOURNAL components. It is used to refer specifically to another iCalendar component, which may be defined in the same collection or externally.

The LINK iCalendar property may be used in any iCalendar component to provide a link to a related resource. Whilst this may seem similar to the RELATED-TO property, a link supports labels and link typing via additional parameters.

The STRUCTURED-DATA iCalendar property supports specifying additional data either inline or via a reference to an external resource. This may include references to alternate representations of a component, such as a vCard for a participant component.

The following properties are used to construct a graph edge from a vCard object to another object.

A vCard defined as a group (via the KIND property) may include references to other vCard objects via the MEMBER property.

A vCard object may also define one or more RELATED properties that refer to another vCard object to represent some kind of relationship.

The FBURL property is used in a vCard object to refer to an iCalendar object representing busy time data for the subject of the vCard.

The CALURI property is used in vCard to refer to related iCalendar objects.