assign 1

THE FOUR PHASE OF METHOD FOR MODELLING COMPLEX SYSTEMS
Hamad I. Odhabi
Ray J. Paul
Robert D. Macredie

Centre for Applied Simulation Modelling (CASM)
Department of information Systems and Computing
Brunel University
Uxbridge, Middlesex UB8 3PH, UNITE KINGDOM



This paper investigates the attempt to combine some different tools in order to build or make a simulation environment that can be used to model complex system. The tools used in this project or research are the four phase method, a simulation world view derived from the three phase approach especially for Object-Oriented and iconic and arcs; iconic representation that represents the actual system components and logic through using icons and arcs; Object-Oriented Programming and the MODSIM simulation library. They on using the discrete-event simulation modeling since it offers the people the chance to develop an understanding of their problem domain by building a simulation of the problem space in which they are interested. There are three broad perspectives that also being used as a basis of this paper which focuses on how to approach the development of simulation models.
The first perspective focuses on using a graphical user interface also known as GUI that allows user to build the model on the screen, connect the components by arcs to represent the model logic, and run the simulation (Drury and Laughery 1994). The second perspective is underpinned by the belief that no simulation program is able to model all types of system behavior without making some simplifications or modifications (Joines 1994). And lastly, the third perspective on which the paper will fully focus , concentrates on using a GUI that is able to automatically generate code, with the modeler making changes to the generated code to match the system needs (Hlupic and Paul 1994). The researchers are more concerned with two basic issues.
The first one concerns the modeling approach. Several programming approaches, often known as ‘simulation world views’, have been designed for discrete-event simulation modeling. The aim of any approach used should be to aid the production of a valid, working simulation at minimum cost or in shortest time (Pidd 1992.a)
The second issue concerns with the effect that cost of modifying the generated code which is the programming me4thodology. There are specific methodologies, reflecting particular programming paradigms which may support simplified model code comprehension, and therefore maintenance. Object-Oriented Programming (OOP), for example, has become popular in simulation modeling (Kienbaum and Paul 1994b), with a claim for relative ease of maintenance being made for the approach.
To address the both issues of modeling approach and programming methodology, this research was made. They introduce a new simulation world view termed the Four Phase Method (FPM), and discuss the importance in the context of iconic representations and the automatic generation of code.
The aim of the research is to attempt to combine a new simulation world view, OOP, and iconic representation to construct a simulation environment for the development of discrete-event simulation models. The modeling environment should be able to model complex system behavior, provide the user with a simple iconic representation to ‘drive’ the model design, and generate understandable code.


EVALUATION:

This research paper was actually, as stated above, about simulation which will create a new simulation world view which they named as the Four Phase Method (FPM). In which, they aimed to combine a new simulation world view or FPM, OOP, and iconic representation to construct a simulation environment for the development of discrete-event simulation models. It is where the modeling environment should be able to model complex systems behavior, provide the user with a simple iconic representation to ‘drive’ the model design, and generate understandable code.
The research paper was very organized from the introduction until to the conclusion of the paper. The variables are carefully explained and evaluated maybe because the writers/researchers are shall we say experts on the information technology industry. In model lay-outing and problem description, they stated that the problem being investigated is not of principal importance to the work, since it is mainly concerned with the modeling process on its own right. It could be an investigation of production quantity or the calculation of the average time that is required to produce a product. Identifying their problem in my point of view is somewhat unclear there were terms that as a normal person will be unclear. Since not all understands technical term.






SAEDES++: DETERMINING COMPLEX SYSTEM AVAILABILITY VIA SIMULATION



Javier Faulin

Department of Statistics and OR
Campus Arrosadia
Public University of Navarre
Pamplona, Navarre 31006, SPAIN


Angel A. Juan
Carles Serrat

Department of Applied Mathematics I
Av. Doctor Marañon, 44-50
Technical University of Catalonia
Barcelona, 08028, SPAIN

Vicente Bargueño

Department of Applied Mathematics I
ETS Ingenieros Industriales
Universidad Nacional de Educacion a Distancia
Madrid, 28080, SPAIN






This paper presents the researchers’ basic ideas behind a simulation-based method, called SAEDES, which can very useful when determining the availability for a wide range of complex systems. The method is implemented in C/C++ using two different algorithms, SAEDES_A1 (component-oriented) and SAEDES_A2 (system-oriented).The two case-studies are introduced and analyzed using both algorithms, which allows them to compare the associated results and became the basis. The ultimate objective of this method is to determine or estimate a complex system availability using the following information which is assumed to be known: system logical structure and failure-times and repair-times distributions for each component. The method is implemented using two different algorithms, SAEDES_A1 which uses MS and can be considered as component-oriented in the sense that it is based on the generation of each component history) and SAEDES_A2 which uses DES and can be considered as system-oriented in the sense that it is based on the generation of the system history.
The method presented in this paper, SAEDES, has been designed to deal with any kind of logical or physical system that meets some general criteria. The following assumptions are made:
1. Two-state systems: at any given time, the system will be either operational which is working properly or not
2. Coherent systems: the analyzed system is assumed to be coherent, in other words: if every component is operative the system will be operative, if no component is operative the system will not be operative, and a positive status change in a component (that is, from inoperative to operative) cannot cause a negative status change in the system (that is, the system will not change its status from operative to no operative)
3. Minimal paths decomposition: the system logical structure is known and it can be expressed in the form of minimal paths
4. Component failure-times and repair-times distributions: for each component, its associated failure-times and repair-times distributions are perfectly known
5. Maintainability policy: system is under a continuous inspection policy, that is any failure will be detected as soon as it will appear
6. Perfect reparations or substitutions: when a component fails, it is repaired or substituted by a new one; in any case, the result is as if a new component has been placed
7. Failure-times and repair-times independence: the failure-times associated to one specific component are independent from the failure-times associated to any other component; the same holds true for repair times.

Assumptions (1) to (4) guarantee that there is enough information to study the system reliability. Assumption (3) often requires a detailed analysis of logical relationships among components. In this sense, simulation algorithms have been proposed to find out the minimal path decomposition of a complex system (Lin and Donaghey 1993). In the assumption (4) context, statistical methods such as accelerated live tests (Meeker and Escobar 1998) and data fitting techniques (Leemis 2003) are usually required. Assumptions (5) and (6) are not restrictive in the sense that they could be relaxed, if necessary, by adapting the algorithms of the method.
Finally, assumption (7) is the most restrictive one and it may require considering some abstraction levels in the system decomposition.

SAEDES method and algorithms make use of several mathematical concepts and techniques. Specifically, the method is based on:
• System availability theory: system reliability and availability concepts, including minimal paths
theory (Barlow and Proschan 1996, Hoyland and Rausand 1994, Kovalenko et al. 1997, Pham (2003)
• Simulation techniques: data fitting, pseudorandom number generation, event treatment, and variance reduction methods (Banks 1998, Chung 2004, Law and Kelton 2000, L’Ecuyer 2002, Wang and Pham 1997)
• Probability and statistical concepts: probability theory, descriptive statistics and inference techniques (Ross 1996).


SAEDES can be very helpful for system managers and engineers in determining and improving complex systems availability. SAEDES is able to provide useful information about complex systems availability and can be applied in most situations where analytical methods are not well suited. Two different and alternative algorithms have been developed to perform SAEDES core functions. Both algorithms have been implemented as computer programs and used separately to analyze different complex systems. Different case studies have been conducted, showing that results from both algorithms are convergent, which contributes to validate the method and to add credibility to it.



EVALUATION:


Hmmmn.. This research paper (for me) is actually good. It’s just there are parts of the paper that is unclear such as using an acronym which they doesn’t include the meaning of it. If I were an ordinary person with no knowledge about technical term used in a computer industry, I won’t be able to understand it. I think the author should put the meaning in every acronym they used. Well, it’s just my own opinion.




Environmental Tobacco Smoke and Tobacco Related Mortality in a Prospective Study of Californians, 1960-98

James E. Enstrom
Geoffrey C. Kabat


The paper tackles about the tobacco which the main objective is to measure the relation between environmental tobacco smoke, as estimated by smoking in spouses, and long term mortality from tobacco related disease. This paper covers 39 years of prospective cohort study. Their main outcome measures the relative risks and the large percentage confidence intervals for deaths from coronary heart disease, lung cancer, and chronic obstructive pulmonary disease related to smoking in spouses and active cigarette smoking. The results for participants followed from 1960 until 1998 the age adjusted relative risk (95% confidence interval) for never smokers married to ever smokers compared with never smokers married to never smokers was 0.94 (0.85 to 1.05) for coronary heart disease, 0.75 (0.42 to 1.35) for lung cancer, and 1.27 (0.78 to 2.08) for chronic obstructive pulmonary disease among 9619 men, and 1.01 (0.94 to 1.08), 0.99 (0.72 to 1.37), and 1.13 (0.80 to 1.58), respectively, among 25 942 women. No significant associations were found for current or former exposure to environmental tobacco smoke before or after adjusting for seven confounders and before or after excluding participants with pre-existing disease. No significant associations were found during the shorter follow up periods of 1960-5, 1966-72, 1973-85, and 1973-98.As years pass by, the percentage of smoking tobacco becomes bigger and the risk of death becomes larger. As a conclusion, the results of their survey do not support a casual relation between environmental tobacco smoke and coronary heart disease and lung cancer may be considerably weaker than generally believed.


Evaluation:

Actually, I was a little bit confused here not because of the research paper but because of the questions that pops up in my mind. I was confused because I was thinking if the research I summarized could be categorized as a scientific research. Well when I search the word “sample scientific research”, it appears. I guess it’s one of the “scientific researches”. Going back to the paper, figures and the way it is presented is good enough to understand by any individual.