Tango object naming (device, attribute and property)

Tango object naming (device, attribute and property)#

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The schema used to identify tango objects is called Tango Resource Locator.

Device name#

A Tango device name is a three fields name. The field separator is the / character. The first field is named domain, the second field is named family and the last field is named member. A tango device name looks like

domain/family/member

It is a hierarchical notation. The member specifies which element within a family. The family specifies which kind of equipment within a domain. The domain groups devices related to which part of the experiment they belong to. At ESRF, some of the machine control system domain name are SR for the storage ring, TL1 for the transfer line 1 or SY for the synchrotron booster. For experiment, ID11 is the domain name for all devices belonging to the experiment behind insertion device 11. Here are some examples of Tango device name used at the ESRF:

  • sr/d-ct/1 : The current transformer. The domain part is sr for storage ring. The family part is d-ct for diagnostic/current transformer and the member part is 1.

  • fe/v-pen/id11-1 : A Penning gauge. The domain part is fe for front-end. The family part is v-pen for vacuum/penning and the member name is id11-1 to specify that this is the first gauge on the front-end part after the insertion device 11.

Full object name#

The device name as described above is not enough to cover all Tango usage like device servers without database or device access for multi control systems. With the naming schema, we must also be able to name attribute and property. Therefore, the full naming schema is

[protocol://]\[host:port/\]device_name\[/attribute][->property][#dbase=xx]

The protocol, host, port, attribute, property and dbase fields are optional. The meaning of these fields are:

protocol: Specifies which protocol is used (tango or taco). tango is the default.

#dbase=xx: The supported value for xx is yes and no. This field is used to specify that the device is a device served by a device server started with or without database usage. The default value is dbase=yes. See the File Database for an howto using #dbase=no at the client side.

host:port: This field has different meaning according to the dbase value. If dbase=yes (the default), the host is the host where the control system database server is running and port is the database server port. It has a higher priority than the value defined by the TANGO_HOST environment variable. If dbase=no, host is the host name where the device server process serving the device is running and port is the device server process port.

attribute: The attribute name

property: The property name

The host:port and dbase=xx fields are necessary only when creating the DeviceProxy object used to remotely access the device. The -> characters are used to specify a property name.

Some examples#

Full device name examples#

  • gizmo:20000/sr/d-ct/1 : Device sr/d-ct/1 running in a specified control system with the database server running on a host called gizmo and using the port number 20000. The TANGO_HOST environment variable will not be used.

  • tango://freak:2345/id11/rv/1#dbase=no : Device served by a device server started without database. The server is running on a host called freak and use port number 2345. freak:2345/id11/rv/1#dbase=no is also possible for the same device.

  • taco://sy/ps-ki/1 : Taco device sy/ps-ki/1

Attribute name examples#

  • id11/mot/1/Position : Attribute position for device id11/mot/1

  • sr/d-ct/1/Lifetime : Attribute lifetime for Tango device sr/d-ct/1

Attribute property name#

  • id11/rv/1/temp->label : Property label for attribute temp for device id11/rv/1

  • sr/d-ct/1/Lifetime->unit : The unit property for the Lifetime attribute of the sr/d-ct/1 device

Device property name#

  • sr/d-ct/1->address : address property for device sr/d-ct/1

Class property name#

  • Starter->doc_url : doc_url property for a class called Starter

Device and attribute name alias#

Within Tango, each device or attribute can have an alias name defined in the database. Every time a device or an attribute name is requested by the API’s, it is possible to use the alias. The alias is simply an open string stored in the database. The rule of the alias is to give device or attribute name a name more natural from the user/scientist’s point of view. Let’s imagine that for an experiment, the sample position is described by angles called teta and psi in text books. It is more natural for scientists when they move the motor related to sample position to use teta and psi rather device name like idxx/mot/1 or idxx/mot/2. An attribute alias is a synonym for the four fields used to name an attribute. For instance, the attribute Current of a power-supply device called sr/ps/dipole could have an alias DipoleCurrent. This alias can be used when creating an instance of a AttributeProxy class instead of the full attribute name which is sr/ps/dipole/Current. Device alias names are unique within a Tango control system. Attribute alias name are also unique within a Tango control system.

Allowed characters and length restrictions#

The device name, the command name, the attribute name, the property name, the device alias name and the device server name are all case insensitive.

In general names must only use letters (a-z), digits (0-9) and underscore (_) and they must start with a letter.

The allowed maximum lenghts for each component are:

Item

Max length

device name

255

domain field

85

family field

85

member field

85

device alias name

255

attribute name

255

property name

255

Aliases follow the naming scheme and maximum lengths of the object they are pointing to.

The RFC project has the gritty nitty details about acceptable characters and maximum lengths: