This paper presents the design considerations and implementation technics of an open system TX, a kernel for distributed database systems developed by the database group of the computer science department at Tsinghua University from 1987 to 1990. TX has played important roles in their further research on distributed database system,knowledge based system, and hypertext database since it was partially implemented. The focuses of this paper are the architecture, data organization, query, processing, data dictionary, and concurrency control of TX.