A distributed real-time database for heterogeneous computer control systems

The authors have developed a real-time distributed database management system (RTDDBMS) which manages data transparently in a heterogeneous, geographically distributed and an open system enviroment. In the authors´ scheme, the data is managed on each resource as a set of tables or relations. Access to data is transparent of its physical location as access requests are handled by the database kernel. A copy of the database kernel resides on each node of the system. These kernels communicate with each other and also with client applications. All communications are through a set of predefined messages. The kernel does not distinguish between messages received from client applications and messages received from a remote kernel. Further, data is classified as local, remote and replicated. When a kernel receives a request for access to a particular data it checks to see if it is locally available. If it is not, then the kernel checks to identify the node(s) at which is available. It then, like any client application, frames a message and sends a request to the kernel of that remote node. The kernel that has the data, which may be the local kernel, on receiving the request for the particular data item performs the desired transaction on it. After performing the transaction it returns the status of the transaction to the client application