Understanding Simulations: Real or Fantasy Worlds Represented with Objects and UML - Prof., Exams of Computer Science

Download Understanding Simulations: Real or Fantasy Worlds Represented with Objects and UML - Prof. and more Exams Computer Science in PDF only on Docsity! 1 Introduction to Simulations CS1316: Representing Structure and Behavior Story  What’s a simulation? Why do we simulate? • Discrete vs. Continuous • Resources  Building software to be modifiable: Software Engineering • Building models out of objects: aggregation, generalizing and specializing  Continuous Simulations • Predatory-prey: Wolves and Deer • Changing our simulation • Creating hungry wolves • Other options: Hungry deer? Deer sex? Wolf sex?  How do we compare simulations? • Creating text files Wildebeests as Simulations Simulations  “A simulation is a representation of a system of objects in a real or fantasy world. The purpose of creating a computer simulation is to provide a framework in which to understand the simulated situation, for example, to understand the behavior of a waiting line, the workload of clerks, or the timeliness of service to customers. A computer simulation makes it possible to collect statistics about these situations, and to test out new ideas about their organization.” • Adele Goldberg & David Robson, Smalltalk-80: The Language and Its Implementation (Addison-Wesley, 1989) 2 Simulations and Objects  Object-oriented programming was invented, in part, to make simulations easier to build!  The characteristics of objects make them more like real world objects, e.g., • Each thing knows some stuff and knows how to do some stuff. • Objects get things done by asking each other to do things. • Your internals are private, unless you want to make them otherwise. Continuous vs. Discrete Simulations  Two main kinds of simulations in the world.  Continuous: Each moment of time is simulated. • When every moment counts.  Discrete: Skip to the important moments. • Want to simulate 100 years? Resources  Resources are points of coordination in a simulation. • Examples: A cashier, a library book, a parking space on a ferry, a jelly bean.  Some resources are fixed and others are produced and consumed.  Some resources are renewable and shared.  Others are coordinated. • Example: For a surgeon to do a surgery, the patient must meet the surgeon at the operating table (the resource) When an object has to wait…  What happens if you (or your proxy object) need a resource and it’s not available? • You wait in a queue • A list that is first-in-first-out (FIFO) 5 A UML Class Diagram +run() -wolves -deer WolfDeerSimulation +setAgent() +getAgent() -myTurtle AgentNode +getNext() +remove() +count() +add() -next LLNode +act() +getClosest() Wolf Turtle +act() +die() Deer * -myTurtle1 * -wolves1 * -deer 1 -mySim 1 * -mySim1 * Unified Modeling Language (UML)  This is a UML class diagram. • A graphical notation for describing the relationships between classes in a model.  UML is a standard that describes several different kinds of diagrams. • Collaboration diagrams: How objects work together and how they call on one another. • Sequence diagrams: What the order of events are in an object system. A class in a UML class diagram Name of the class Instance variables or fields: What the class instances know Operations or methods: What the instances know how +run() -wolves -deer WolfDeerSimulation Generalization-specialization relationships Turtle +act() +die() Deer A Deer is a subclass of Turtle: It’s a specialization of Turtle 6 Associations WolfDeerSimulation has two AgentNodes in it: One to represent wolves and one to represent deer. AgentNodes don’t know their simulation +run() -wolves -deer WolfDeerSimulation +setAgent() +getAgent() -myTurtle AgentNode * -wolves1 * -deer 1 A Class Diagram describes the Model, without the Code +run() -wolves -deer WolfDeerSimulation +setAgent() +getAgent() -myTurtle AgentNode +getNext() +remove() +count() +add() -next LLNode +act() +getClosest() Wolf Turtle +act() +die() Deer * -myTurtle1 * -wolves1 * -deer 1 -mySim 1 * -mySim1 *