ItemFlow without and with itemProperty - and compatible ItemFlows

Gallery

Tutorial

TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo

Section

09:01: Indicating flow on Associations and Connectors

Tags and keywords

UML keywords

InformationFlow::conveyed

Connector

internal structure compartment

SysML keywords

ItemFlow

Block

part property

ItemFlow::itemProperty

Slide kind

SysML Block Definition Diagram (BDD)

There is now also a BIG REFERENCE CARD on ItemFlows showing how to use them to capture communication views in various SysML diagrams:

Webel: SysML: Heard of "follow the money"? In MBSE we "follow the flows"! Identify requests, data packets, messages, signals early on and use ItemFlow as often as you can wherever you can! Adopt a signal processing mindset throughout (systems thinking).

The primary function of the SysML ItemFlow is:

SysML-1.6: 'Item flows specify the things that flow between blocks and/or parts and across associations or connectors.'

SysML-1.6: 'Whereas flow properties specify what “can” flow in or out of a block, item flows specify what “does” flow between blocks and/or parts in a particular usage context.'

SysML-1.6: 'This important distinction enables blocks to be interconnected in different ways depending on its usage context.'

The full power of ItemFlow can be leveraged by also using an 'itemProperty':

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We can see that ItemFlow is primarily intended to be used in combination with FlowProperty.

SysML-1.6: 'Item flows on connectors shall be compatible with flow properties of the blocks usages at each end of the connector, if any. The direction of the item flow shall be compatible with the direction of flow specified by the flow properties.'

Note these compatible constraints:

SysML-1.6: 'FlowProperty::1_restricted_types A FlowProperty shall be typed by a ValueType, Block, or Signal.'

SysML-1.6: 'ItemFlow::2_type_restricted An ItemFlow itemProperty shall be typed by a ValueType, Block, or Signal.'

To explore the capabilities if ItemFlow further we now look deeper into the SysML FlowProperty in the next section.

Up next

09:02: Ports - The basics

Notes

Snippets (quotes/extracts)

[SysML-1.6] Item flows specify the things that flow between blocks and/or parts and across associations or connectors.

[SysML-1.6] Whereas flow properties specify what “can” flow in or out of a block, item flows specify what “does” flow between blocks and/or parts in a particular usage context.

[SysML-1.6] This important distinction enables blocks to be interconnected in different ways depending on its usage context.

[SysML-1.6] An ItemFlow describes the flow of items across a connector or an association. It may constrain the item exchange between blocks, block usages, or ports as specified by their flow properties.

[SysML-1.6] One can label an ItemFlow with the classifiers of the items that may be conveyed. For example: a label Water would imply that instances of Water might be transmitted over this ItemFlow.

[SysML-1.6] The itemProperty attribute has no values if the item flow is realized by an Association.

[SysML-1.6] FlowProperty::1_restricted_types A FlowProperty shall be typed by a ValueType, Block, or Signal.

[SysML-1.6] An ItemFlow describes the flow of items across a connector or an association. The notation of an item flow is a black arrowhead on the connector or association. The arrowhead is towards the target element.

[SysML-1.6] For an item flow with an item property, the label shows the name and type of the item property (in name: type format). Otherwise the item flow is labeled with the name of the classifier of the conveyed items.

[SysML-1.6] Item flows on connectors shall be compatible with flow properties of the blocks usages at each end of the connector, if any. The direction of the item flow shall be compatible with the direction of flow specified by the flow properties.

[SysML-1.6] In addition, if the item flow identifies an item property, then one can label the item flow with the item property.

[SysML-1.6] For example, a label of "liquid: Water" means Water items might flow and these items are the values of the property "liquid," i.e., the values of the "liquid" item property are the instances of Water flowing at any given time.

[SysML-1.6] ItemFlow::itemProperty : Property [0..1] An optional property that relates the flowing item to the instances of the connectors enclosing block. This property is applicable only for item flows realized by connectors. The itemProperty attribute has no ...

[SysML-1.6] The target flow property type shall be the same as, or a generalization of, a classifier of the item flow or the source flow property type, whichever is more specialized.

[SysML-1.6] ItemFlow::2_type_restricted An ItemFlow itemProperty shall be typed by a ValueType, Block, or Signal.

[SysML-1.6] The item flow in each case specifies what “does” flow on the connector in the particular usage (e.g., gas, water) and the flow property specifies what can flow (e.g., fluid). This enables type matching between the item flows and between flow properties...

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Visit also (backlinks)

SysMLv1: An ItemFlow without an assigned 'itemProperty' is sometimes informally/casually referred to as an "information flow", especially when applied to an Association (because it is much like a UML InformationFlow), but formally it is a SysML ItemFlow.

SysML: Whether you use a Block, ValueType, or Signal to represent something that flows (and can be applied to an ItemFlow) depends on what you want to achieve. If you want to indicate something structured with value properties with Units use a Block.

Related slides (includes other tutorials)

WaterProcessingPlant - FlowProperty and ItemFlow example with Ports (in BDD with structure)

WaterProcessingPlant - FlowProperty and ItemFlow example with Ports (in IBD with verbose Port compartments)

Figure 9-5: Item Flow Stereotype

Figure 9-16: Usage example of item flow decomposition

Figure 9-17: Usage example of item flow decomposition

Figure 15-5: Example of flow allocation from ObjectFlow to Connector

Figure D.19 - Internal Structure of the Power Subsystem (Internal Block Diagram)

Figure D.39 - Flow Allocation to Power Subsystem (Power Functional Allocation)

Related slides (backlinks, includes other tutorials)

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