The ability to let users search for products conveniently in product database is critical to the success of e-commerce. Although structured query languages (e.g. SQL) can be used to effectively access the product database, it is very difficult for end users to learn and use. In this paper, the authors study how to optimize search over structured product entities (represented by specifications) with keyword queries such as \"Cheap gaming laptop\". One major difficulty in this problem is the vocabulary gap between the specifications of products in the database and the keywords people use in search queries.