.BusinessSimulation.UsersGuide.Tutorial.ElementaryBuildingBlocks

Stocks describe the states of a system, such as a measurable quantity that could, in principle, be measured even if the system were hypothetically "frozen."

Flows are aggregate processes that change the states of a system by filling or draining stocks at a certain rate.

Sources or Sinks act as stocks with infinite capacity ("clouds") at a system's boundary, from or into which elements flow. The BSL broadens the definition to include the combination of a stock with infinite capacity and a connected flow to model processes of growth or decline from external influences.

Converters model information processing on a fundamental level, transforming information input into information output immediately.

Information sources provide inputs from external "information processors" or "controllers" that lie outside a system's boundary.

These are pre-built components for modeling information processing, decision-making, or subsystems more generally.

Information Levels store information that changes over time due to the flow of information. We may use an information level to model a company's assets, liabilities, and shareholders' equity.

Material Stocks represent physical quantities, such as living beings and people, raw material, finished goods, or capital equipment, that change due to material flows. Unlike information levels, material stocks can never become negative. If a flow tries to drain an empty material stock, it will be set to zero.

Capacity Restricted Stocks are material stocks with additional capacity restriction. They may have maximum and a minimum levels (≥ 0).

An n-th order exponential delay will delay its inflow so that the actual times of residence will be distributed around the indicated (mean) delay time. The variation for the distribution of residence times will decrease with higher delay orders (a delay of infinite order will behave exactly like a PureDelay).

A material delay with fixed delay time that may change over time. Any changes in the delay time will only affect incoming material, so that new material may flow out earlier than material already in the stock.

As in an ideal conveyor belt, everything that enters is delayed by a fixed amount of time, which cannot change during the simulation.

This stock also models an ideal conveyor, but the discretely modeled component allows the delay time to change during the simulation. Unlike a PureDelay, the order of inflow is preserved so that material may leave the belt at the same time, but never ahead of material that has entered earlier.

The Oven (aka batch delay) is an ideal model of a batch production process:  Material will flow into the oven until its capacity is reached (or the load time is exceeded). The material will then be processed for some process time and will then be unloaded. During the processing material can neither flow in nor out of the stock.

Unidirectional flows drain the stock connected to their portA (→FlowPort) and fill the stock connected to their portB at an identical rate. The rate needs to be positive and will be set to zero if it is negative, as the direction of flow cannot change during a simulation.

Bidirectional flows are essentially unidirectional flows that may change the direction of flow during a simulation depending on the sign of the rate:  A negative rate will transport entities from B to A, while a positive rate will transport entities from A to B.

Interactions model the general case of two stocks having netflows flow from/to clouds (positive rates will fill the connected stock), which may be influenced by the stock levels. A simple example is the →BrokenTransition, where the inflow to stock B is proportional to the rate of the outflow of stock A, as some kind of transformation is modeled rather than a mere transition.

A Cloud simply is a stock that is outside a system's boundary—here we assume that the stock has an infinite capacity. In models of population dynamics, clouds will be used as sources for newborns or sinks for the deceased.

A Source combines a cloud with a unidirectional outflow that will then fill the connected stock.

A Sink combines a cloud with a unidirectional inflow that will then drain the connected stock.

A SourceOrSink combines a cloud with a bidirectional flow that may fill or drain a stock depending on the sign of the flow's rate: A positive rate, by convention, fills the connected stock.

DiscreteDelay converters introduce discrete behavior or delays into information processing and typically contain an information level—which is the reason for their boxlike-appearance.

Logical converters have Boolean outputs (→BooleanOutput) and/or inputs (→BooleanInput).

Lookup converters use tabular or more elaborate parametric functions to model the transformation of information.

Vector converters have vector inputs and/or outputs.

Taking the raw information from the system and its environment and bringing it into the form needed for decision making.

Using (preprocessed) information, we will have some decision rule that will give a decision output—usually goals and other regulations to be observed or rates for processes that change the state(s) of the system.

Blocks do not exchange physical quantities with other systems. Instead there is only exchange of information for managerial control or information processing.

Incubators receive, store, and provide physical entities via multiple stock ports. There will often be some kind of transformation during storage.

Transceivers not only receive and store physical quantities, but also move them to/from connected systems. With multiple stock and flow ports, these are the most general kind of subsystems.

Actuators move physical entities to and from connected systems via multiple flow ports (push or pull). Subsequently, there may also be some storage as internal processes of transformation take up time.