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Real-time database systems can have security constraints in addition to timing constraints. Such real-time systems are typically contained in environments that exhibit hierarchical propagation of information, where mandatory access control for security is required. Conventional multilevel secure (MLS) database models that implement mandatory access control are inadequate for time-critical applications and conventional real-time database models do not address security constraints. The objective of this work is to incorporate security constraints in real-time database systems in such a way that not only is security achieved, but achieving security does not degrade real-time performance significantly in terms of deadlines missed. We present two concurrency control algorithms for secure real-time databases: the Secure two-phase locking high priority (2PLHP) algorithm is based on a two-phase locking protocol and the Secure optimistic concurrency control (OPT) algorithm uses the properties of an optimistic concurrency protocol. We implement the two algorithms and study their performance using a real-time database system simulation model. Our study covers both soft and firm real-time databases. Results show that both the algorithms perform fairly well in terms of security and timeliness compared to non-secure algorithms. We show that achieving increased security does not necessarily mean an increased sacrifice in real-time performance.

A real-time database system has temporal consistency constraints in addition to timing constraints. The timing constraints require a transaction to be completed by a specified deadline, and the temporal consistency constraints require that temporal data read by a transaction be up-to-date. If a transaction reads out-of-date data, it will become temporally inconsistent. A real-time database system consists of different types of temporal data objects, including derived objects. The value of a derived object is computed from a set of other objects, known as the read-set of the derived object. The derived object may not always reflect the current state of its read-set; a derived object can become out-of-date even if its read-set is up-to-date. Any subsequent transaction reading the derived object will then become temporally inconsistent. In this case, in order to read up-to-date objects, a transaction will have to wait until some other transaction updates the out-of-date object. However, in doing so, the waiting transaction may miss its deadline, particularly if the update is not periodic but instead arrives randomly. We propose to update the outdated objects so that not only is the temporal consistency improved, but also the number of missed deadlines does not increase significantly, and as a result there is an overall improvement in the performance of the system. We propose, implement and study a novel approach, to be known as triggered updates, to improve temporal consistency in firm real-time database systems when updates are not periodic. We identify properties of triggered updates and explain how they work by giving both an intuitive and a probabilistic analysis. We present strategies for generating triggered updates, discuss their suitability in various contexts and perform a detailed simulation study to evaluate their performance. Results show that it is possible to improve temporal consistency without degrading the timeliness of real- time database systems to a great deal.

Many real-time database systems, such as military institutions and government agencies, are contained in environments that exhibit restricted access of information, where mandatory access control for security is required. Hence, in addition to timing constraints, real-time database systems have security constraints. Conventional multi-level secure database models are inadequate for time-critical applications and conventional real-time database models do not support security constraints. The objective of this work is to incorporate security constraints in real-time database systems in such a way that not only is security achieved, but achieving security does not degrade real-time performance significantly in terms of deadlines missed. We propose a new optimistic concurrency control algorithm for secure firm real-time databases. Results show that the algorithm performs fairly well in terms of security and timeliness compared to a non-secure algorithm. We argue and show that achieving more security does not necessarily mean more sacrifice in real-time performance.

Many real-time database systems are contained in environments that exhibit restricted access to information, such as government agencies, hospitals and military institutions, where mandatory access control for security is required. In addition to such security constraints, real-time database systems have real-time integrity constraints. These real-time constraints require deadlines to be met and data to be temporally consistent. Conventional multi-level secure database models are inadequate for time-critical applications and conventional real-time database models do not support security constraints. We propose a new concurrency control algorithm for secure real-time databases. We implement the algorithm and study the performance using a real-time database system simulation model. Results show that the algorithm performs fairly well in terms of security and timeliness compared to the non-secure algorithm. We argue and show that achieving more security does not necessarily mean a great deal of sacrifice in maintaining real-time constraints.