**9. References**


188 Real-Time Systems, Architecture, Scheduling, and Application

Most of the research about the optimism concurrency control method are focus on how reduces unnecessary transactions restarts and the transactions near to completed missing its deadline. The most research is based on dynamic adjustment serialization method. When the transactions access temporal data with time limit, the traditional concurrency control method cannot schedule effectively because it is not consider data-deadline. This chapter improved the validation phase rules and proposed an optimistic concurrency control method based on temporal data (RTCC-DD), which considered the influence between temporal data time limit and the transaction deadline. Theoretical analysis and experimental results demonstrate that the RTCC-DD method can outperform the previous ones for reducing effectively unnecessary restart number of transactions and more suitable for real-

The chapter is sponsored by the National Natural Science Foundation of China under Grant No. 41176082, 61073182; Heilongjiang Natural Science Foundation under Grant No. F201024; The Fundamental Research Funds for the Central Universities No. HEUCFZ1010,

A. Brad, K. Ben and G. M. Hector. Database support for efficiently maintaining derived data.

A. Fishwick. SIMPACK: Getting started with simulation programming in C and C++.

D. Menasce and T. Nakanishi. Optimistic versus pessimistic concurrency control

H. T. Kung and J. T. Robinson. On optimistic methods for concurrency control. ACM

J. Huang, J. A. Stankovic, K. Ramamritham, and D. Towsley. Experimental evaluation of

J. Huang, J. A. Stankovic, K. Ramamritham, and D. Towsley. On using priority inheritance

J. Lee and S. H. Son. Using dynamic adjustment of serialization order for real-time database

J. Lee. Concurrency Control Algorithms for Real-Time Database Systems. PhD thesis,

75, Raleigh-Durham, NC, USA, 1993. IEEE Computer Society Press.

Department of Computer & Information Science, University of Florida, 1992. IEEE

mechanisms in database management systems. Information Systems, 7(1):13–27,

real-time optimistic concurrency control schemes. In Proceedings of the 17th VLDB Conference, pages 35–46, Barcelona, Catalonia, Spain, September 1991. Morgan

in real-time databases. In Proceedings of the 12th IEEE Real-Time Systems Symposium, pages 210–221, San Antonio, Texas, USA, 1991. IEEE Computer

systems. In Proceedings of the 14th IEEE Real-Time Systems Symposium, pages 66–

Faculty of the School of Engineering and Applied Science, University of Virginia,

Technical Report, Stanford University, 1995: 223~240.

Transactions on Database Systems, 6(2):213–226, June 1981.

time database system.

**8. Acknowledgment** 

HEUCF100602.

**9. References** 

1982.

Kaufmann.

Society Press.

January 1994.

Computer Society Press


**0**

**9**

*France*

**Quality of Service Scheduling**

**in the Firm Real-Time Systems**

*University of Nantes, IRCCyN UMR CNRS 6597*

Audrey Queudet-Marchand and Maryline Chetto

Real-time systems are those in which the time at which the results are produced is important. The correctness of the result of a task is not only related to its logical correctness, but also to when the results occur (Stankovic, 1988). In order to characterize their requirements, real-time systems are traditionaly classified as follows: *hard, soft* and *firm* (Liu, 2000). It is imperative that all time constraints are met in hard real-time systems. In contrast, firm or soft real-time systems do not have as stringent timeliness requirements allowing for some degree of tardiness (soft) or miss ratio (firm). Many researches within the soft and firm real-time area have focused on minimizing tardiness and/or miss ratio but without quantifying acceptable levels. In this chapter, we focus on scheduling firm periodic tasks which have additional requirements. These requirements specify the minimum acceptable completion ratios that should be met in order to maintain system correctness. In a hard real-time system all hard deadline tasks must meet their deadlines to maintain system correctness; otherwise, the system has failed. In contrast, a deadline is considered to be soft if it can be missed occasionally. A task that misses a single soft deadline is not considered a failure. Correctness in a soft real-time system is determined by the degree to which timeliness has been enforced for the entire task set. However, the completion of a tardy firm deadline task is not meaningful

since late delivery of the result is considered to be of no value to the real-time system.

enforced for firm real-time tasks. This is the subject of this chapter.

Although firm deadlines can occasionally be missed, there is normally an upper limit to the number of misses within a defined interval. The hard real-time paradigm is well established and it has received considerable attention by researchers and practitioners within the academe and the industry alike. Numerous techniques and algorithms – especially in the area of scheduling – have been developed. Most scheduling algorithms developed for soft and firm real-time systems lack the ability to enforce constraints on the upper limit of misses. Unbounded consecutive time constraint violations may occur without such an enforcement. Realistically, if consecutive instances of a task fail to complete before their deadlines, then the system will eventually suffer from a failure. This indicates that there are additional constraints. These constraints express the minimum degree of timeliness that must be

**1. Introduction**

**1.1 What does firm real-time mean?**

Y. Y. Wang, Q. Wang, H. A. Wang. Dynamic adjustment of execution order in real-time database. In Proceedings of 18th International Parallel and Distributed Processing Symposium, 2004. 1219~1225.
