Keyword-based search is well studied in the world of text documents and Internet search engines. While traditional database management systems offer powerful query languages, they do not allow keyword-based search. In this paper, we discussed ITREKS, a system that support efficient keyword-based search over relational database by indexing tuple relationship: A basic database tuple relationship, FDJT, is established in advance. Then a FDJT-Tuple-Index table is created, which records relationships between each tuple and FDJT. At query time, for each of keywords, system first finds tuples in every relation that contain it, using full text indexes offered by database management system. Then use FDJT-Tuple-Index table to find the joinable tuples contain all keywords in the query.