openhab-docs/concepts/items.md

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Items

Eclipse SmartHome has a strict separation between the physical world (the "things", see below) and the application, which is built around the notion of "items" (also called the virtual layer).

Items represent functionality that is used by the application (mainly user interfaces or automation logic). Items have a state and are used through events.

The following item types are currently available (alphabetical order):

Item Name	Description	Command Types
Color	Color information (RGB)	OnOff, IncreaseDecrease, Percent, HSB
Contact	Item storing status of e.g. door/window contacts	OpenClose
DateTime	Stores date and time	-
Dimmer	Item carrying a percentage value for dimmers	OnOff, IncreaseDecrease, Percent
Group	Item to nest other items / collect them in groups	-
Image	Holds the binary data of an image	-
Location	Stores GPS coordinates	Point
Number	Stores values in number format	Decimal
Player	Allows to control players (e.g. audio players)	PlayPause, NextPrevious, RewindFastforward
Rollershutter	Typically used for blinds	UpDown, StopMove, Percent
String	Stores texts	String
Switch	Typically used for lights (on/off)	OnOff

Group Items

Group items collect other items into groups. Group items can themselves be members of other group items. Cyclic membership is not forbidden but strongly not recommended. User interfaces might display group items as single entries and provide navigation to its members.

Example for a Group item as a simple collection of other items:

    Group groundFloor
    Switch kitchenLight (groundFloor)
    Switch livingroomLight (groundFloor)

Derive Group State from Member Items

Group items can derive their own state from their member items. To derive a state the group item must be constructed using a base item and a group function. When calculating the state, group functions recursively traverse the group's members and also take members of subgroups into account. If a subgroup however defines a state on its own (having base item & group function set) traversal stops and the state of the subgroup member is taken.

Available group functions:

Function	Parameters	Base Item	Description
EQUALITY	-	<all>	Sets the state of the members if all have equal state. Otherwise UNDEF is set.
AND, OR, NAND, NOR	,	<all> (must match active & passive state)	Sets the <activeState>, if the member state <activeState> evaluates to true under the boolean term. Otherwise the <passiveState> is set.
SUM, AVG, MIN, MAX	-	Number	Sets the state according to the arithmetic function over all member states.
COUNT		Number	Sets the state to the number of members matching the given regular expression with their states.

Examples for derived states on group items when declared in the item DSL:

• Group:Number:COUNT(".*") counts all members of the group matching the given regular expression, here any character or state (simply count all members).
• Group:Number:AVG calculates the average value over all member states which can be interpreted as DecimalTypes.
• Group:Switch:OR(ON,OFF) sets the group state to ON if any of its members has the state ON, OFF if all are off.
• Group:Switch:AND(ON,OFF) sets the group state to ON if all of its members have the state ON, OFF if any of the group members has a different state than ON.

State and Command Type Formatting

StringType

StringType objects store a simple Java String.

DateTimeType

DateTimeType objects are parsed using Java's SimpleDateFormat.parse() using the first matching pattern:

1. yyyy-MM-dd'T'HH:mm:ss.SSSZ
2. yyyy-MM-dd'T'HH:mm:ss.SSSX
3. yyyy-MM-dd'T'HH:mm:ssz
4. yyyy-MM-dd'T'HH:mm:ss

DecimalType, PercentType

DecimalType and PercentType objects use Java's BigDecimal constructor for conversion. PercentType values range from 0 to 100.

HSBType

HSB string values consist of three comma-separated values for hue (0-360°), saturation (0-100%), and value (0-100%) respectively, e.g. 240,100,100 for blue.

PointType

PointType strings consist of three DecimalTypes separated by commas, indicating latitude and longitude in degrees, and altitude in meters respectively.

Enum Types

Type	Supported Values
IncreaseDecreaseType	INCREASE, DECREASE
NextPreviousType	NEXT, PREVIOUS
OnOffType	ON, OFF
OpenClosedType	OPEN, CLOSED
PlayPauseType	PLAY, PAUSE
RewindFastforwardType	REWIND, FASTFORWARD
StopMoveType	STOP, MOVE
UpDownType	UP, DOWN

A note on items which accept multiple state data types

There are a number of items which accept multiple state data types, for example DimmerItem, which accepts OnOffType and PercentType, RollershutterItem, which accepts PercentType and UpDownType, or ColorItem, which accepts HSBType, OnOffType and PercentType. Since an item has a SINGLE state, these multiple data types can be considered different views to this state. The data type carrying the most information about the state is usually used to keep the internal state for the item, and other datatypes are converted from this main data type. This main data type is normally the first element in the list returned by Item.getAcceptedDataTypes().

Here is a short table demonstrating conversions for the examples above:

Item Name	Main Data Type	Additional Data Types Conversions
Color	HSBType	• OnOffType - OFF if the brightness level in the HSBType equals 0, ON otherwise • PercentType - the value for the brightness level in the HSBType
Dimmer	PercentType	OnOffType - OFF if the brightness level indicated by the percent type equals 0, ON otherwise
Rollershutter	PercentType	UpDownType - UP if the shutter level indicated by the percent type equals 0, DOWN if it equals 100, and UnDefType.UNDEF for any other value