<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script type="text/javascript">
    var products=[
        ["blue","medium"],     //产品1
        ["blue","small"],        //产品2
        ["red","medium"]    //产品3
    ];
    function select_item(){
        //根据上面的products数组
        //点击blue,因为blue对应的有2种size，下面的size 2个都能选
        //点击red,只存在1种size，给下面<li><a href="#">small</a></li> 加css (addClass("not_selectable"))
        //点击small,只存在1种color，上面的<li><a href="#">red</a></li> 加css (addClass("not_selectable"))
        //点击medium,存在2种color，上面的color 2个都能选
    }
</script>
<style type="text/css">
    .not_selectable{color:gray;}
</style>
<div class="properties">
    <dl>
        <dt>color</dt>
        <dd>
            <ul>
                <li><a href="#">blue</a></li>
                <li><a href="#">red</a></li>
            </ul>
        </dd>
    </dl>
    <dl>
        <dt>size</dt>
        <dd>
            <ul>
                <li><a href="#">small</a></li>
                <li><a href="#">medium</a></li>
            </ul>
        </dd>
    </dl>
</div>