Database Management Systems (DBMS) based on the Relational Theory are designed to meet the needs of storing and retrieving large amounts of data. These data can be represented by numeric values, dates, and/or small strings, and are generically called "scalar data". With the evolution of information technology, it is increasingly necessary to organize, store, and retrieve other types of data. In this work, we call such data "complex data", such as images, videos, time series, and genetic sequences. Comparisons based on Identity Relations or Order Relations are useful for querying scalar data but are not suitable for complex data. For complex data, similarity queries have been the most studied option, although their availability in existing DBMS is still limited. Metric Access Methods (MAMs) usually are applied for indexing complex data to speed-up similarity queries. This Master's project aimed at incorporating MAM resources to a Relational DBMS, by proposing and implementing a technique for extending a widely used Relational DBMS. Thus, we implemented the existing Slim-Tree MAM into PostgreSQL, which is a Relational DBMS. This implementation resulted in RAFIKI, a prototype capable of outperforming its predecessor system KIARA, in terms of speed, in the task of performing similarity queries. The experimental analysis carried showed that RAFIKI is up to 6 times faster than KIARA. Further, using the proposed technique, it is possible to extend PostgreSQL to support other MAMs.