Design A

<?php

class Committee
{
    protected $id;
    protected $shortName;
    protected $longName;
}

class Proposal
{
    protected $committeeHeardBy;
    protected $committeeOnAgenda;
}

Committee:
{
    id: 1
    shortName: "G"
    longName: "International Building Code - General Code Committee"
}

Proposal:
{
    id: 1
    committeeHeardBy: 1
    committeeOnAgenda: 1
}

Design B

<?php

class Committee
{
    protected $id;
    protected $shortName;
    protected $longName;
    protected $purpose;
}

class Proposal
{
    protected $committeeHeardBy;
    protected $committeeOnAgenda;
}

Committee:
{
    id: 1
    shortName: "G"
    longName: "International Building Code - General Code Committee"
    purpose: "Hearing"
}

Committee:
{
    id: 2
    shortName: "G"
    longName: "International Building Code - General Code Committee"
    purpose: "Agenda"
}

Proposal:
{
    id: 1
    committeeHeardBy: 1
    committeeOnAgenda: 2
}