URL parsing and sessions in Reservation system - php

Question

I am creating a flight/hotel reservation system like farecompare.com Farecompare parse values to other sites and create sessions other sites too. Anyone tell me how they create sesssions in it. I can parse url but i am not able to create sessions.
public function flight($depart, $return, $from, $to, $type, $class,
$adults, $seniors, $children) {
$dep = explode("/", $depart);
$ret = explode("/", $return);
if ($type == 'RoundTrip') {
$expurl = 'http://www.expedia.co.in/Flights-Search?trip=' .
strtolower($type) . '&leg1=from%3A' . $from .
'%29%2Cto%3A' . $to .
'%29%2Cdeparture%3A' . $dep[1] .
'/'.$dep[0].'/'.$dep[2].
'TANYT&leg2=from%3A' . $to .
'%29%2Cto%3A' . $from .
'%29%2Cdeparture%3A' .
$ret[1].'/'.$ret[0].'/'.$ret[2] .
'TANYT&passengers=children%3A' . $children .
'%2Cadults%3A' . $adults .
'%2Cseniors%3A' . $seniors .
'%2Cinfantinlap%3AY&options=cabinclass%3Aeconomy'.
'%2Cnopenalty%3AN%2Csortby%3Aprice&mode=search';
echo 'Expedia';
} else {
$type = 'oneway';
$expurl = 'http://www.expedia.co.in/Flights-Search?trip='.
strtolower($type) . '&leg1=from%3A' . $from .
'%29%2Cto%3A' . $to . '%29%2Cdeparture%3A' .
$dep[1].'/'.$dep[0].'/'.$dep[2] .
'TANYT&passengers=children%3A' . $children .
'%2Cadults%3A' . $adults .
'%2Cseniors%3A' . $seniors .
'%2Cinfantinlap%3AY&options=cabinclass%3Aeconomy'.
'%2Cnopenalty%3AN%2Csortby%3Aprice&mode=search';
echo 'Expedia';
}
}
I worked on Expedia by parsing url to get data but there are other sites like cheapoait, travelocity etc which uses sessions. How to create sessions?

Answer 1

I would assume they store it in the cookies.

Answer 2

We can not access session data of other domain on our site. Data transfer done using web services SOAP OR REST in form of XML. That can be retrieved on other domain and store in session and cookies and use for calculation in website.