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1 Introduction

1-6

What Is an Entity?

Discrete-event simulations typically involve discrete items of interest. By definition,

these items are called entities in SimEvents software. Entities can pass through a

network of queues, servers, gates, and switches during a simulation. Entities can carry

data, known in SimEvents software as attributes.

Note: Entities are not the same as events. Events are instantaneous discrete incidents

that change a state variable, an output, and/or the occurrence of other events. See “What

Is an Event?” on page 1-7 for details.

Examples of entities in some sample applications are in the table.

Context of Sample Application Entities

Airport with a queue for runway access Airplanes waiting for access to runway

Communication network Packets, frames, or messages to transmit

Bank of elevators People traveling in elevators

Conveyor belt for assembling parts Parts to assemble

Computer operating system Computational tasks or jobs

A graphical block can represent a component that processes entities, but entities

themselves do not have a graphical representation. When you design and analyze your

discrete-event simulation, you can choose to focus on:

• The entities themselves. For example, what is the average waiting time for a series of

entities entering a queue?

• The processes that entities undergo. For example, which step in a multiple-step

process (that entities undergo) is most susceptible to failure?

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