Engineering topics

Gligor, V. D.

Publications and source records attributed to Gligor, V. D..

4 records

NASA NTRS1984

Interconnecting heterogeneous database management systems

It is pointed out that there is still a great need for the development of improved communication between remote, heterogeneous database management systems (DBMS). Problems regarding the effective communication between distributed DBMSs are primarily related to significant differences between local data managers, local data models and representations, and local transaction managers. A system of interconnected DBMSs which exhibit such differences is called a network of distributed, heterogeneous DBMSs. In order to achieve effective interconnection of remote, heterogeneous DBMSs, the users must have uniform, integrated access to the different DBMs. The present investigation is mainly concerned with an analysis of the existing approaches to interconnecting heterogeneous DBMSs, taking into account four experimental DBMS projects.

Gligor, V. D.↗

NASA NTRS1980

On deadlock detection in distributed systems

A hierarchically organized and a distributed protocol for deadlock detection in distributed databases are presented in a previous study Menasce and Muntz (1979). In this paper, it is shown that the distributed protocol is incorrect, and possible remedies are presented. However, the distributed protocol remains impractical because 'condensations' of 'transaction-wait-for' graphs make graph updates difficult to perform. Delayed graph updates cause the occurrence of false deadlocks in this as well as in some other deadlock detection protocols for distributed systems. The performance degradation that results from false deadlocks depends on the characteristics of each protocol.

Gligor, V. D.↗

NASA NTRS1979

Review and revocation of access privileges distributed through capabilities

The problems of review and revocation of access privileges are presented in the context of the systems that use capabilities for the long-term distribution of access privileges. The approach to solve these two problems requires that a capability propagation graph be maintained in memory spaces associated with subjects (e.g., domains, processes, etc.) that make copies of the respective capability; the graph remains inaccessible to those subjects, however. Parallel processes of the operating system update the graph as the system runs. It is noted that the most important application of the above mechanisms may prove to be the possibility of implementing a capability-based system in which the capability representation is short.

Gligor, V. D.↗

NASA NTRS1979

Object migration and authentication

The paper presents a mechanism permitting a type manager to fabricate a migrated object representation which can be entrusted to other subsystems or transmitted outside of the control of a local computer system. The migrated object representation is signed by the type manager in such a way that the type manager's signature cannot be forged and the manager is able to authenticate its own signature. Subsequently, the type manager can retrieve the migrated representation and validate its contents before reconstructing the object in its original representation. This facility allows type managers to authenticate the contents of off-line or network storage and solves problems stemming from the hierarchical structure of the system itself.

Gligor, V. D.↗