===== Items and Flows =====

==== Flow Properties ====

An item is information, energy or matter transferrable between blocks. Blocks can have **flow properties** to characterise what //can// be flow in/out of blocks. Flow properties can be typed by Value Types (e.g. tempC) or Blocks (e.g. Water, however the Water block will need to have value properties).

**Item flows**, on the other hand, are what //actually// flows between blocks.

Flow occurs between parts if
  * flow properties in both parts are of the same type
  * (OR downstream flow property is **more general** than the upstream flow property)
  * direction shall be consistent (one property is inout, or both properties are opposite direction)

Below I create the item that I want to flow. Note that it has a value property of tempC.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow8.png?400 |}}

In the BDD I add **flow properties** on Part blocks that are the conduits of what can flow. Note that the direction (in, out) is defined. In the Whole block I added two **item properties** which are the items that actually flow.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow9-0.png?600 |}}

In the IBD I add connectors that connect the part blocks and item flows that carry the item properties. Note that the item properties shown on the connector is the item property of the **Whole** block.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow10-0.png?600 |}}
==== Item Flows ====

In Association Blocks we covered how to define connectors. However what to do if you want to define the flows that occur on that connector? This is done with Item Flows.

{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow1.png?300 |}}
Following on from the Power Sub-system IBD add a connector between two properties. Call this connector 'someCable' (note that if we wanted to define the **connector** then we should use Association Blocks covered earlier). The connector name is elided.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow2.png?300 |}}
From the tool box use Item Flow relationship to create an item flow from ': Power Source_Motor' to ': Controller Motor'.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow3.png?300 |}}

=== Type Item Flow by Classifier ===

Right click the information flow and Advanced -> Information Items Conveyed... -> Add
Find the Item Flow you want. It can be a block or (if simple) then a ValueType. In this case we want the item flow to be DC electricity which is modelled as a Block. 
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow4.png?350 |}}

Right click on the connector and Advanced -> Information Flows Realized..
Check the box for the information flow you just created. Click OK.
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow6.png?300 |}}
Done
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow7.png?300 |}}

=== Type Item Flow by Property ===

Double click on Item Flow. In Tags->Item Property search for **upstream** property. Typically this is a flow property.

{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow11.png?300 |}}

Right click on the connector (which we named someCable) and Advanced -> Information Flows Realized..
Check the box for the information flow you just created. Click OK.

{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow12.png?600 |}}

Done
{{ :bok:eng:mbse:sysml:bbd-ibd:infoflow13.png?300 |}}