Design And Implementation Of User Defined Type In DM3

With the change of application, the disadvantage of the traditional RDBMS which can't support user defined type (UDT) has become more and more obvious. To meet the need, the function of UDT is added to DM3 which is the pratical database system researched and developed by ourselves.To support the UDT, we adopt two ways to design the module. As the result of the two strategies integrated, on one hand, one packaging layer put on the kernel of DBMS server is used to deal with the usual object data. On the other hand, some special functions such as user defined function (UDF) are implemented by extending the kernel of system.The UDT include not only data but also operation on the data. On the side of data, we implement the single UDT based on the pre-defined data type and the structured UDT, even the reference to the UDT, and the structured UDT can be inherited or nested by the other structured UDT. The logical information of UDT is inserted into the new dictionary table, and the object identifier make up of identifier of one table and identifier of one item. Because the size of dictionary is distinctly enlarged, we also introduce the new algorithm named LRU related with content to keep the system performance.On the side of operation, the function developed by java or c language can run in the new server of DM3. To ensure the security of the server, the c function runs on the separate process from the server. The java function utilize the mechanism of JVM to solve the same problem. During extending the DM3 server, we also put forward the algorithm which is used to recognize different fucntions of same name.