Abstract: NITDB is a multi-user relational DBMS developed on a high-perfor-?nce microcomputer system at Nanjing Institute of Technology.Some problems emerging from the design and implementation of library of functions for performing relational operations in NITDB are discussed in this paper.Algorithms for different relational operations,such as sequential retrieval,bounded sequential retrieval,bounded binary sequential retrieval,retrieval via secondary indices,retrieval via a clustering indexed sequential organization.nested-loop join,merge-scan join and join using a clustering indexed sequential organization,are introduced.The efficiency of each algorithm is discussed and demonstrated with data actually measured on the running system.