Calculate Family Relationship from Genealogical Data

Question

I would like to be able to calculate the family relationship between two individuals in a family tree, given the following data schema (simplified from my actual data schema, on

Answer 1

Below is my PHP implementation of my algorithm to calculate relationship. This is based upon the data schema I outlined in the original question. This only finds the "closest" i.e. shortest-path relationship between the two individuals, it does not resolve compound relationships such as half-siblings or double cousins.

Note that data access functions such as get_father and get_gender are written in the style of a database abstraction layer I always use. It should be fairly straightforward to understand what is going on, basically all dbms-specific functions such as mysql_query are replaced with generalized functions such as db_query; it is not very complicated at all, especially in the examples in this code, but feel free to post questions in comments if it isn't clear.

 $c_anc) {
    $distance = $c_anc[1] + $c_anc[2];
    if ($least_distance < 0 || $least_distance > $distance) {
      $least_distance = $distance;
      $ld_index = $i;
    }
  }

  return $ld_index >= 0 ? $common_ancestors[$ld_index] : false;
} //END function lowest_common_ancestor

function common_ancestors($a_id, $b_id) {
  $common_ancestors = array();

  $a_ancestors = get_ancestors($a_id);
  $b_ancestors = get_ancestors($b_id);

  foreach ($a_ancestors as $a_anc) {
    foreach ($b_ancestors as $b_anc) {
      if ($a_anc[0] == $b_anc[0]) {
        $common_ancestors[] = array($a_anc[0], $a_anc[1], $b_anc[1]);
        break 1;
      }
    }
  }

  return $common_ancestors;
} //END function common_ancestors

function get_ancestors($id, $dist = 0)
{
  $ancestors = array();

  // SELF
  $ancestors[] = array($id, $dist);

  // PARENTS
  $parents = get_parents($id);
  foreach ($parents as $par) {
    if ($par != 0) {
      $par_ancestors = get_ancestors($par, $dist + 1);
      foreach ($par_ancestors as $par_anc) {
        $ancestors[] = $par_anc;
      }
    }
  }

  return $ancestors;
} //END function get_ancestors

function get_parents($id)
{
  return array(get_father($id), get_mother($id));
} //END function get_parents

function get_father($id)
{
  $res = db_result(db_query("SELECT father_id FROM child WHERE child_id = %s", $id));
  return $res ? $res : 0;
} //END function get_father

function get_mother($id)
{
  $res = db_result(db_query("SELECT mother_id FROM child WHERE child_id = %s", $id));
  return $res ? $res : 0;
} //END function get_mother

function get_gender($id)
{
  return intval(db_result(db_query("SELECT gender FROM individual WHERE id = %s", $id)));
}

function ordinal_suffix($number, $super = false)
{
  if ($number % 100 > 10 && $number %100 < 14) {
    $os = 'th';
  } else if ($number == 0) {
    $os = '';
  } else {
    $last = substr($number, -1, 1);

    switch($last) {
      case "1":
        $os = 'st';
        break;
      case "2":
        $os = 'nd';
        break;
      case "3":
        $os = 'rd';
        break;
      default:
        $os = 'th';
    }
  }

  $os = $super ? ''.$os.'' : $os;

  return $number.$os;
} //END function ordinal_suffix

function format_plural($count, $singular, $plural)
{
  return $count.' '.($count == 1 || $count == -1 ? $singular : $plural);
} //END function plural_format

?>

As I had mentioned previously, the algorithm to determine LCA is far less than optimal. I plan to post a separate question to optimize that, and another to address the problem of calculating compound relationships such as double cousins.

Many thanks to everyone who helped prod me in the right direction! With your tips, this turned out to be much easier than I originally thought.