%% You should probably cite draft-ietf-calext-ical-relations instead of this I-D.
@techreport{douglass-ical-relations-04,
    number =    {draft-douglass-ical-relations-04},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-douglass-ical-relations/04/},
    author =    {Mike Douglass},
    title =     {{Support for Icalendar Relationships}},
    pagetotal = 18,
    year =      2015,
    month =     jan,
    day =       14,
    abstract =  {This specification updates RELATED-TO and introduces new iCalendar properties LINK, STRUCTURED-CATEGORY and REFID to allow better linking and grouping of iCalendar components and related data.},
}