Column.php

<?php
class ZendDbSchema_Db_Schema_Table_Column
    extends ZendDbSchema_Db_Schema_Table_AbstractDefinition
{
    protected function _getSchemaKey()
    {
        return ZendDbSchema_Db_Schema_Table::COLUMNS_KEY;
    }

    protected function _getDropSql()
    {
        return $this->getTable()->getGenerator()->dropColumn($this);
    }

    protected function _getAlterSql()
    {
        return $this->getTable()->getGenerator()->alterColumn($this);
    }

    protected function _getCreateSql()
    {
        return $this->getTable()->getGenerator()->createColumn($this);
    }

    public function isNullable()
    {
        return (bool) $this->__get('nullable');
    }

    public function isSigned()
    {
        return (bool) $this->__get('signed');
    }
}