Bisame/database/migrations/2016_03_12_215913_create_words_table.php

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateWordsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('words', function(Blueprint $table) {
            $table->increments('id');
            $table->timestamps();
            $table->string('value');
            $table->integer('sentence_id')->unsigned()->nullable();
            $table->foreign('sentence_id')->references('id')->on('sentences');
            //$table->integer('postag_id')->unsigned()->nullable();
            //$table->foreign('postag_id')->references('id')->on('postags');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('words');
    }
}