The Server object processes an incoming entity and then passes it to the next object.
Entities that are waiting to be processed are held by a Queue object identified by the keyword WaitQueue. All entities received by the Server first pass through this Queue object, even if the Server is Idle. Entities can be sent to the Server or directly to the Queue. The choice has no effect on the model logic.
Whenever an entity is added to a Queue, all the Servers and other type of objects that specified this Queue as its WaitQueue will be notified. The first one that is available will then remove the entity for processing.
The rate at which entities are processed is determined by the ServiceTime keyword. This input has the units of time and can be a constant value, an object that returns a number with units of time (e.g. TimeSeries or Probability Distribution), or an expression that returns such a number.
The operation of a Server can be stopped by threshold closures, scheduled maintenance, and by breakdown events as controlled by the inputs to its various Threshold, Maintenance, and Breakdown keywords.
Although a Server is alerted automatically when an entity arrives to its WaitQueue, it is NOT alerted automatically when its Match input changes or when an expression entered WaitQueue keyword changes the Queue it returns. The WatchList keyword provides a way to alert the Server to these types of changes.
Normally, a Server picks the first object from its queue for processing. However, it is possible to select any of the other objects in the queue using the Match, SelectionCondition, and NextEntity keywords. These inputs can be used separately or together to specify the objects that are eligible to be selected.
Server Inputs
Keyword |
Description |
Key Inputs |
|
Description |
A free-form string describing the object. |
NextComponent |
The next object to which the processed entity is passed. |
WaitQueue |
Queue from which the next entity for processing will be selected. If an expression is entered that can return various Queues, it is necessary for each Queue to be included in the entry to the WatchList keyword. If a Queue is not included, then the arrival of an entity to that Queue will not wake up this processor. |
Match |
An expression returning a string value that determines which of the queued entities are eligible to be selected. If used, the only entities eligible for selection are the ones whose inputs for the Queue's Match keyword are equal to value returned by the expression entered for this Match keyword. Expressions that return a dimensionless integer or an object are also valid. The returned number or object is converted to a string automatically. A floating point number is truncated to an integer. Note that a change in the Match value does not trigger the processor automatically to re-check the Queue. The processor can be triggered by adding one or more objects to the WatchList input. |
SelectionCondition |
An optional expression that tests whether an entity in the queue is eligible to be processed. The expression should return 1 (true) if the entity is eligible. The entity chosen for processing is the first one in the queue that satisfies both the SelectionCondition expression and the Match value (if specified). Unlike the Match value, which must be specified when an entity first enters the queue, the SelectionCondition is evaluated when an entity is to be removed from the queue. Consequently, a SelectionCondition is more flexible than a Match value, but is significantly less efficient. |
NextEntity |
An optional expression that returns the next entity to be removed from the queue. No entity is removed if the expression returns null or the entity is not present in the queue. To be removed, the entity must also satisfy the Match and SelectionCondition inputs if these are entered. |
WatchList |
An optional list of objects to monitor. The queue will be inspected for an entity to process whenever one of the WatchList objects changes state. |
ServiceTime |
The service time required to process an entity. |
Options |
|
AttributeDefinitionList, CustomOutputList |
See Section 6.2. |
StateAssignment |
The state to be assigned to each entity on arrival at this object. No state is assigned if the entry is blank. |
Thresholds |
|
ImmediateThresholdList, ImmediateReleaseThresholdList, OperatingThresholdList, ReleaseThresholdList |
See Section 10.1. |
Maintenance |
|
WorkingStateList, ImmediateMaintenanceList, ForcedMaintenanceList, OpportunisticMaintenanceList, ImmediateBreakdownList, ForcedBreakdownList, OpportunisticBreakdownList |
See Section 10.2. |
Format |
|
StateGraphics |
A list of state/DisplayEntity pairs. For each state, the graphics will be changed to those for the corresponding DisplayEntity, e.g. { Idle DisplayEntity1 } { Working DisplayEntity2 } |
ProcessPosition |
The position of the entity being processed relative to the processor. |
Graphics |
|
Position, Alignment, Size, Orientation, Region, RelativeEntity, DisplayModel, Show, Movable, VisibleViews, DrawRange |
See Section 11.1. |
Server Outputs
Output Name |
Description |
Entity and DisplayEntity |
|
Name, ObjectType, SimTime, Parent, Position, Size, Orientation, Alignment, GraphicalLength, ObserverList, NextList, PreviousList, EntityReferenceList |
See Section 11.1. |
StateEntity |
|
State, WorkingState, WorkingTime, StateTimes, TotalTime |
See Section 10.3. |
StateUserEntity |
|
Idle, Working, Setup, Maintenance, Breakdown, Stopped, Utilisation, Commitment, Availability, Reliability, Open, NextMaintenanceTime, NextBreakdownTime |
See Section 10.2. |
LinkedDevice |
|
obj, NumberAdded, NumberProcessed, NumberInProgress, ProcessingRate, ReleaseTime |
See Section 16. |
LinkedService |
|
MatchValue |
The present value to be matched to an entity in the queue. |
Server |
|
ServiceDuration |
The total working time required for the present service activity. |
ServicePerformed |
The working time that has been completed for the present service activity. |
FractionCompleted |
The portion of the total service time for the present service activity that has been completed. |
User-defined attributes and custom outputs |
As defined by the AttributeDefinitionList and CustomOutputList inputs. |