DTJ Number 3 September 1987 - Digital Technical Journals

The NMCCjDECnet Monitor DesignKERNEL INFORMATIONMANAGER(KIM)- --- - -- - --Figure 5NMCC Kernelphysical database that uses Digital's RdBJVMSsoftware . This relational database system waschosen because it provides data integrity, its datamodel is similar to the NMCC data model, and itoffered a simple method for handling sets ofrecords.The physical database is contained within alogical database (LDB) system. LDB providestransaction services and abstracts the operationson the database, thus masking from the rest of thesystem the detailed knowledge of how the databaseis implemented. The interface to LDB isasynchronous, allowing the rest of the system toproceed with other actions while data is readfrom or written to the disk. Because the interfaceto the RdBJVMS software is synchronous, LDB isimplemented as multiple server processes separatefrom the kernel. Each server is synchronizedwith its database transaction.The logical database is contained within thekernel information manager (KIM) , to whichall requests to read or modify data are made .The actions performed by KIM are atomic, meaningthey act as a single unit even though composedof more primitive actions. KIM's clientsare thus freed from needing detailed knowledgeof the transactions. But KIM's most importanttask is providing a uniform way to request historicaland real-time data. This uniformity greatlysimplifies the design of all other parts of thecode. The user interface and reports packagedo not need special code to perform historicalor real-time functions. Instead, they only haveto perform some simple data manipulations;KIM handles all the intricacies of detailedprocessing. Many functions are clusteredaround KIM, all of which use it to access theirdata.134Digital Tecbnical]ournalNo. 3 September 1986