Object Process Methodology - Wikipedia
however, sensors require some time to adjust to changes, and in many cases exhibit the static sensitivity of the measuring system. We express the relationship between input and output for a general of four types of inputs: .. o A system consisting of a spring, a mass, and a damper can model many. Physical systems are tangible entities that may be static or dynamic in operation. Abstract systems relationships among sets of variables or models – the abstract .. Step 5: For each binary M:N relationship type R, create a new relation S whose . Menu: With a menu dialogue, a menu displays a list of alternate selections. A model is a precise representation of a system's dynamics used to an- .. terconnection. The static relation between inputs and outputs can easily be established An experiment of this type tells directly if the process is nonlinear. A simple way to determine .. and it is know to exhibit very interesting dynamics. Figure
Burns know how to build this type of guitar from scratch based on its blueprints. Each guitar constructed from the class can be referred to as an instance or object of the class, and so my guitar in Figure is an instance of the Burns BMS Guitar class.
This is what differentiates OO from other forms of system development. In OO, closely related state and behavior are combined into class definitions, which are then used as the blueprints from which objects can be created.
To complete the description, we need to know what the guitar can do. This includes behavior such as tuning and playing the guitar. Operations " later in this chapter.
For example, my BMS guitar might have a scratch on the back—or several—but if I am creating a class that will represent BMS guitars, do I need to add attributes that contain details about scratches?
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I might if the class were to be used in a repair shop; however, if the class were to be used only in the factory system, then scratches are one detail that I can hopefully ignore. Discarding irrelevant details within a given context is called abstraction. If Burns were creating a model of its guitar production system, then it would probably be interested in creating a Burns BMS Guitar class that models how one is constructed, what materials are to be used, and how the guitar is to be tested.
In contrast, if a Guitar World store were creating a model of its sales system, then the Burns BMS Guitar class might contain only relevant information, such as a serial number, price, and possibly any special handling instructions. Getting the right level of abstraction for your model, or even just for a class, is often a real challenge.
Focus on the information that your system needs to know rather than becoming bogged down with details that may be irrelevant to your system. Tip Abstraction is key not only to class diagrams but to modeling in general. A model, by definition, is an abstraction of the system that it represents. The actual system is the real thing; the model contains only enough information to be an accurate representation of the actual system. In most cases, the model abstracts away details that are not important to the accuracy of the representation.
According to the object-oriented approach to system development, for an object to be an object, it needs to contain both data—attributes—and the instructions that affect the data—operations. This is the big difference between object orientation and other approaches to system development: Referring back to the guitar analogy, the Burns BMS Guitar class could encapsulate its strings, its body, its neck, and probably some neat electrics that no one should mess around with.
These parts of the guitar are effectively its attributes, and some of the attributes, such as the strings, are accessible to the outside world and others, such as electrics, are hidden away. At a minimum, the guitar class should at least have an operation called play so that the guitar objects can be played, but other operations such as clean and possibly even serviceElectrics may also be encapsulated and offered by the class.UML Class Diagram Tutorial
Encapsulation of operations and data within an object is probably the single most powerful and useful part of the object-oriented approach to system design. Encapsulation enables a class to hide the inner details of how it works from the outside world—like the electrics from the example guitar class—and only expose the operations and data that it chooses to make accessible. Encapsulation is very important because with it, a class can change the way it works internally and as long as those internals are not visible to the rest of the system, those changes will have no effect on how the class is interacted with.
At its simplest, a class in UML is drawn as a rectangle split into up to three sections. The top section contains the name of the class, the middle section contains the attributes or information that the class contains, and the final section contains the operations that represent the behavior that the class exhibits. The attributes and operations sections are optional, as shown in Figure If the attributes and operations sections are not shown, it does not necessarily imply that they are empty, just that the diagram is perhaps easier to understand with that information hidden.
Figure shows a couple of classes from the CMS in Chapter 2: Two classes of objects have been identified in the CMS The interaction diagrams covered in Chapters 7 through 10 are used to show how class instances, or objects, work together when a system is running. Visibility How does a class selectively reveal its operations and data to other classes?
Once visibility characteristics are applied, you can control access to attributes, operations, and even entire classes to effectively enforce encapsulation. See " Encapsulation " earlier in this chapter for more information on why encapsulation is such a useful aspect of object-oriented system design. There are four different types of visibility that can be applied to the elements of a UML model, as shown in Figure Typically these visibility characteristics will be used to control access to both attributes, operations, and sometimes even classes see the " Packages " section in Chapter 13 for more information on class visibility.
Declare an attribute or operation public if you want it to be accessible directly by any other class. The public interface of a class consists of the attributes and operations that can be accessed and used by other classes. This means the public interface is the part of your class that other classes will depend on the most.
It is important that the public interface to your classes changes as little as possible to prevent unnecessary changes wherever your class is used. Public Attributes To have public attributes or to not have public attributes?
That is the question. Many object-oriented designers groan at the use of public attributes: There is just as much potential for abuse. One example where it is generally accepted to use a public attribute is when the attribute is a constant that may be used by a number of different classes.
Attributes that act as constants, i. In this situation, exposing the attribute to the rest of your system is not quite so dangerous since its value cannot be changed. Protected Visibility Protected attributes and operations are specified using the hash symbol and are more visible to the rest of your system than private attributes and operations, but are less visible than public. Declared protected elements on classes can be accessed by methods that are part of your class and also by methods that are declared on any class that inherits from your class.
The system relating inputs to outputs depends on other variables too: Decision variables are sometimes known as independent variables. Exogenous variables are sometimes known as parameters or constants. The variables are not independent of each other as the state variables are dependent on the decision, input, random, and exogenous variables.
Furthermore, the output variables are dependent on the state of the system represented by the state variables. Objectives and constraints of the system and its users can be represented as functions of the output variables or state variables.
The objective functions will depend on the perspective of the model's user. Depending on the context, an objective function is also known as an index of performance, as it is some measure of interest to the user.
Although there is no limit to the number of objective functions and constraints a model can have, using or optimizing the model becomes more involved computationally as the number increases. For example, economists often apply linear algebra when using input-output models.
Complicated mathematical models that have many variables may be consolidated by use of vectors where one symbol represents several variables. The usual representation of this black box system is a data flow diagram centered in the box. Mathematical modeling problems are often classified into black box or white box models, according to how much a priori information on the system is available.
A black-box model is a system of which there is no a priori information available. A white-box model also called glass box or clear box is a system where all necessary information is available. Practically all systems are somewhere between the black-box and white-box models, so this concept is useful only as an intuitive guide for deciding which approach to take.
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Usually it is preferable to use as much a priori information as possible to make the model more accurate. Therefore, the white-box models are usually considered easier, because if you have used the information correctly, then the model will behave correctly.
Often the a priori information comes in forms of knowing the type of functions relating different variables. For example, if we make a model of how a medicine works in a human system, we know that usually the amount of medicine in the blood is an exponentially decaying function.
But we are still left with several unknown parameters; how rapidly does the medicine amount decay, and what is the initial amount of medicine in blood? This example is therefore not a completely white-box model.
These parameters have to be estimated through some means before one can use the model. In black-box models one tries to estimate both the functional form of relations between variables and the numerical parameters in those functions. Using a priori information we could end up, for example, with a set of functions that probably could describe the system adequately. If there is no a priori information we would try to use functions as general as possible to cover all different models.
An often used approach for black-box models are neural networks which usually do not make assumptions about incoming data. Alternatively the NARMAX Nonlinear AutoRegressive Moving Average model with eXogenous inputs algorithms which were developed as part of nonlinear system identification  can be used to select the model terms, determine the model structure, and estimate the unknown parameters in the presence of correlated and nonlinear noise.
The advantage of NARMAX models compared to neural networks is that NARMAX produces models that can be written down and related to the underlying process, whereas neural networks produce an approximation that is opaque. Subjective information[ edit ] Sometimes it is useful to incorporate subjective information into a mathematical model. This can be done based on intuitionexperienceor expert opinionor based on convenience of mathematical form.
Bayesian statistics provides a theoretical framework for incorporating such subjectivity into a rigorous analysis: An example of when such approach would be necessary is a situation in which an experimenter bends a coin slightly and tosses it once, recording whether it comes up heads, and is then given the task of predicting the probability that the next flip comes up heads. After bending the coin, the true probability that the coin will come up heads is unknown; so the experimenter would need to make a decision perhaps by looking at the shape of the coin about what prior distribution to use.
Incorporation of such subjective information might be important to get an accurate estimate of the probability. Complexity[ edit ] In general, model complexity involves a trade-off between simplicity and accuracy of the model. Occam's razor is a principle particularly relevant to modeling, its essential idea being that among models with roughly equal predictive power, the simplest one is the most desirable.
Static and Dynamic Characteristics of Instruments
While added complexity usually improves the realism of a model, it can make the model difficult to understand and analyze, and can also pose computational problems, including numerical instability.
Thomas Kuhn argues that as science progresses, explanations tend to become more complex before a paradigm shift offers radical simplification[ citation needed ]. For example, when modeling the flight of an aircraft, we could embed each mechanical part of the aircraft into our model and would thus acquire an almost white-box model of the system. However, the computational cost of adding such a huge amount of detail would effectively inhibit the usage of such a model.
Satisfaction of the process precondition and the subsequent process execution need to consume affect the instance of the activating object. Graphically, an arrow with a closed arrowhead pointing from the object to the process with the small letter e for event.
The syntax of a consumption event link OPL sentence is: Object triggers Process, which consumes Object. Graphically, a bidirectional arrow with closed arrowheads at each end between the object and the process with a small letter e for event. The syntax of an effect event link OPL sentence is: Object triggers Process, which affects Object. OPM state-specified agent event link Basic enabling event links: An agent event link is an enabling link from an agent object to the process that it activates and enables.
Graphically, a line with a filled circle "black lollipop" at the terminal end extending from an agent object to the process it activates and enables with a small letter e for event. The syntax of an agent event link OPL sentence is: Agent triggers and handles Process. An instrument event link is an enabling link from an instrument object to the process that it activates and enables.
Graphically, a line with an empty circle "white lollipop' at the terminal end extending from the instrument object to the process it activates and enables with a small letter e for event. The syntax of an instrument event link OPL sentence is: Instrument triggers Process, which requires Instrument. State-specified transforming event links: State-specified consumption event link: A state-specified consumption event link is a consumption link that originates from a specific state of an object and terminates at a process, which an instance of the object activates.
Satisfaction of the process precondition, including the activating object instance being at its specified state, and the subsequent process execution consume the activating object instance.
Graphically, an arrow with a closed arrowhead pointing from the object state to the process with the small letter e for event. The syntax of a state-specified consumption event link OPL sentence is: Specified-state Object triggers Process, which consumes Object.
Input-output-specified effect event link: An input-output-specified effect event link is an input-output-specified effect link with the additional meaning of activating the affecting process when the object enters the specified input state. Graphically, the input-output-specified effect link with a small letter e for event.
The syntax of an input-output specified effect event link OPL sentence is: Input-state Object triggers Process, which changes Object from input-state to output-state. Input-specified effect event link: An input-specified effect event link is an input-specified effect link with the additional meaning of activating the affecting process when the object enters the specified input state.
Graphically, the input-specified effect link with a small letter e for event. The syntax of an input-specified effect event link OPL sentence is: Input-state Object triggers Process, which changes Object from input-state.
Output-specified effect event link: An output-specified effect event link is an output-specified effect link with the additional meaning of activating the affecting process when the object comes into existence. Graphically, the output-specified effect link with a small letter e for event.
The syntax of an output-specified effect event link OPL sentence is: Object in any state triggers Process, which changes Object to destination-state State-specified agent event link: State-specified agent event link: A state-specified agent event link is a state-specified agent link with the additional meaning of activating the process when the agent enters the specified state.
Graphically, the state-specified agent link with a small letter e for event. The syntax of a state-specified agent event link OPL sentence is: Qualifying-state Agent triggers and handles Processing". State-specified instrument event link: A state-specified instrument event link is a state-specified instrument link with the additional meaning of activating the process when the instrument enters the specified state. Graphically, the state-specified instrument link with a small letter e for event.
The syntax of a state-specified instrument event link OPL sentence is: Qualifying-state Instrument triggers Processing, which requires qualifying-state Instrument. Process invocation is an event of triggering of a process by a process. An invocation link is a link from an invoking process to the process that it invokes triggersmeaning that when the invoking process terminates, it immediately triggers the process at the other end of the invocation link.
Graphically, a lightning symbol jagged line from the invoking process terminating with a closed arrowhead at the invoked process end denote an invocation link. The syntax of an invocation link OPL sentence is: Self-invocation is invocation of a process by itself, such that that upon process termination, the process immediately invokes itself. The self-invocation link shall denote self-invocation. Graphically, a pair of invocation links, originating at the process and joining head to tail before terminating back at the original process denote the self-invocation link.
The syntax of a self-invocation link OPL sentence is: Implicit invocation occurs upon sub-process termination within the context of an in-zoomed process, at which time the sub-process invokes the one s immediately below it. Graphically, there is no link between the invoking and the invoked sub-processes; their relative heights within the in-zoom context of their ancestor process implies this semantics. Condition links A condition link is a procedural link between a source object or object state and a destination process that provides a bypass mechanism, which enables system control to skip the destination process if its precondition satisfaction evaluation fails, otherwise the process waits for the precondition to become true.
A condition consumption link is a condition link from an object to a process, meaning that if in run-time an object instance exists, then the process precondition is satisfied, the process executes and consumes the object instance. However, if that object instance does not exist, then the process precondition evaluation fails and the control skips the process. Graphically, an arrow with a closed arrowhead pointing from the object to the process with the small letter c for condition near the arrowhead shall denote a condition consumption link.
The syntax of the condition consumption link OPL sentence is: Process occurs if Object exists, in which case Object is consumed, otherwise Process is skipped. A condition effect link is a condition link between an object and a process, meaning that if at run-time an object instance exists, and the rest of the process precondition is satisfied, then the process executes and affects the object instance.
Graphically, a bidirectional arrow with two closed arrowheads, one pointing in each direction between the affected object and the affecting process, with the small letter c for condition near the process end of the arrow. The syntax of the condition effect link OPL sentence is: Process occurs if Object exists, in which case Process affects Object, otherwise Process is skipped.
A condition agent link is a condition link from an object to a process, meaning that if at run-time an agent instance exists and the rest of the process precondition is satisfied, then the process executes and the agent handles execution.
However, if that agent instance does not exist, then the process precondition evaluation fails and the control skips the process. Graphically, a line with a filled circle 'black lollipop" at the terminal end extending from an agent object to the process it enables, with the small letter c for condition near the process end. The syntax of the condition agent link OPL sentence is: Agent handles Process if Agent exists, else Process is skipped. A condition instrument link is a condition link from an object to a process, meaning that if at run-time an instrument instance exists and the rest of the process precondition is satisfied, then the process executes.
However, if that instrument instance does not exist, then the process precondition evaluation fails and the control skips the process. Graphically, a line with an empty circle "white lollipop" at the terminal end, extending from an instrument object to the process it enables, with the small letter c for condition near the process end, shall denote a condition instrument link.
The syntax of the condition instrument link OPL sentence shall be: Process occurs if Instrument exists, else Process is skipped. Condition state-specified consumption link: A condition state-specified consumption link is a condition consumption link that originates from a specified state of an object and terminates at a process, meaning that if an object instance exists in the specified state and the rest of the process precondition is satisfied, then the process executes and consumes the object instance.
However, if that object instance does not exist in the specified state, then the process precondition evaluation fails and the control skips the process. Graphically, an arrow with a closed arrowhead pointing from the object qualifying state to the process with the small letter c for condition near the arrowhead.